E a r t h q u a k e T i psLearning Earthquake Design and Construction C . V. R. M u r t y Department of Civil Engineering Indian Institute of Technology Kanpur Kanpur Building Material and Technology Promotion Council Ministry of Urban Development & Poverty Alleviation, Government of India New Delhi March 2005 E a r t h q u a k e T i ps Learning Earthquake Design and Construction Near Far Authored by C . V . R. M u r t y Department of Civil Engineering Indian Institute of Technology Kanpur Kanpur Building Material and Technology Promotion Council Ministry of Urban Development & Poverty Alleviation, Government of India New Delhi Published by: National Information Center of Earthquake Engineering Indian Institute of Technology Kanpur Kanpur 208016 Phone: (0512) 259 7866; Fax: (0512) 259 7794 Email:
[email protected]; Web: www.nicee.org March 2005 PRE F A C E The Republic Day earthquake of 26 January 2001 in Gujarat clearly demonstrated the earthquake vulnerability profile of our country. It created a considerable interest amongst the professionals associated with construction activities in any form, as well as the non-pr ofessi onals regarding the earthquake safety issues. While the subject of earthquake engineering has its own sophisticati on and a lot of new research is being conducted in this very important subje ct, it i s also impor tant to widely disseminate the basic con cepts of earthquake resistant constructions through simple language. With this objective, the Indian Institute of Technol ogy Kanpur (IITK) and the Building Materials and Techn ology Promotion Council (BMTPC), a constituent of the Ministry of Urban Development & Poverty Alleviation, Government of India, launched the IITK-BMTPC Series on Earthquake Tips in early 2002. Professor C. V. R. Murty was requested to take up the daunting task of expressing difficult con cepts in very simple language, which he has very ably done. This publication, containing all the 24 Tips, is targeted at persons interested in building construction. The Tips cover topics such as basic introduction to earthquakes and terminology such as magnitude and intensity, concepts of earthquake resistant design, and aspects of a seismic design and construction of buildings. Utmost care is taken to ensure that despite complexity of the concepts, the Tips are simple and unambiguous. To ensure the highest quality of technical contents, every Tip is carefully reviewed by two or more experts, both within and outside India and their feedback is used before finalizing the Tips. The Tips are released for publicati on to all interested journals, magazines, and newspapers. The Tips are also placed at the web site of the National Information Centre of Earthquake Engineering (NICEE) (www.nicee.org) and Building Materials & Technology Promotion Council (BMTPC) (www.bmtpc.org). The project has succeeded way beyond our own expectations: a large number of journals of architecture, construction and structural engineering, and many prestigious newspapers have published some or all the Tips. Seeing the interest of the readers in the Tips, we are happy to place all the twenty four Tips in this single cover for facilitating their usage. We are grateful to Professor C. V. R. Murty for the dedication with which he worked on this project. We also take this opportunity to thank the numerous reviewers who have willingly spent time in reviewing the Tips. But, a special mention may be made here for Ms. Alpa R. Sheth of Mumbai and Professor Svetlana N. Brzev of Vancouver (Canada), wh o have reviewed very substantial number of these Tips. Finally, we must thank numerous newspapers, journals and magazines who came forward to publish these Tips, at times making an exception to their editorial policy on exclusivity. Development of the Tips was financially supported by the BMTPC New Delhi. Financial support for this reprint and dissemination was provided by the National Programme on Earthquake Engineering Education (www.nicee.org/npeee) and the Joan and Haresh Shah family funds, respectively, which is gratefully acknowledged. We hope that the readers will find the Tips useful when constructing buildings in earthquake prone areas and will consult the expert for finalising their design and construction details. We welcome comments and suggestions; please email to
[email protected]. Sudhir K. Jain Coordinator, National Information Center of Earthquake Engineering & Professor of Civil Engineering Indian Institute of Technology Kanpur Kanpur 208016 March 2005 Li s t o f R e v i e w e r s We are grateful to the following experts who reviewed one or more Earthquake Tip and made valuable feedback. Ms. Alpa R. Sheth, Vakil Mehta Sheth Consulting Engineers, Mumbai Professor Andrew Charleson, Victoria University of Wellington, NEW ZEALAND Dr. C. P. Rajendran, Centre for Earth Science Studies, Trivandrum Professor Christopher Arnold, Building Systems Development, USA Professor Durgesh C. Rai, Indian Institute of Technology Kanpur, Kanpur Professor K. N. Khattri, Wadia Institute of Himalayan Geology, Dehradun Dr. Leonardo Seeber, Lamont-Doherty Earth Observatory, USA Dr. Praveen K. Malhotra, Factory Mutual Research Corporation, USA Professor Robert D. Hanson, The University of Michigan, USA Professor Sri Krishna Singh, Instituto De Geofisica, MEXICO Professor Sudhir K. Jain, Indian Institute of Technology Kanpur, Kanpur Professor Svetlana N. Brzev, British Columbia Institute of Technology, CANADA Mr. T. N. Gupta, BMTPC, New Delhi C O N T E N TS Preface List of Reviewers Tip 01: What Causes Earthquake? 1 Tip 02: How the Ground Shakes? 3 Tip 03: What are Magnitude and Intensity? 5 Tip 04: Where are Seismic Zones in India? 7 Tip 05: What are the Seismic Effects on Structures? 9 Tip 06: How Architectural Features Affects Buildings During Earthquakes? 11 Tip 07: How Buildings Twist During Earthquakes? 13 Tip 08: What is the Seismic Design Philosophy for Buildings? 15 Tip 09: How to Make Buildings Ductile for Good Seismic Performance? 17 Tip 10: How Flexibility of Buildings affects their Earthquake Response? 19 Tip 11: What are the Indian Seismic Codes? 21 Tip 12: How do Brick Masonry Houses behave during Earthquake? 23 Tip 13: Why should Masonry Buildings have simple Structural Configuration? 25 Tip 14: Why are horizontal bands necessary in masonry buildings? 27 Tip 15: Why is vertical reinforcement required in masonry buildings? 29 Tip 16: How to make Stone Masonry Buildings Earthquake Resistant? 31 Tip 17: How do Earthquake affect Reinforced Concrete Buildings? 33 Tip 18: How do Beams in RC Buildings Resist Earthquakes? 35 Tip 19: How do Columns in RC Buildings Resist Earthquakes? 37 Tip 20: How do Beam-Column Joints in RC Buildings Resist Earthquakes? 39 Tip 21: Why are Open-Ground Storey Buildings Vulnerable in Earthquakes? 41 Tip 22: Why are Short Columns more Damaged During Earthquakes? 43 Tip 23: Why are Buildings with Shear Walls Preferred in Seismic Regions? 45 Tip 24: How to Reduce Earthquake Effects on Buildings? 47 . it is of the order like the convective flow of water when heated in a of a couple to tens of centimeters per year. Learning 1 Earthquake Design Earthquake Tip and Construction What Causes Earthquakes? The Earth and its Interio r Long time ago. In another case..5 gm/cc. The Inner Core is solid and consists of heavy metals (e. Large amount of heat was generated by this fusion. 1 Plate Tectonics atmosphere and 1. to slide on the hot molten outer core. varies across the Earth. hot molten lava comes out and the cold rock mass goes Pacific into the Earth. someday. the temperature is estimated to be ~2500 C. This sliding of Earth’s mass Crust takes place in pieces called Tectonic Plates. The surface Mantle of the Earth consists of seven major tectonic plates and many smaller ones (Figure 3). The differentiated Earth consists of the Inner Core (radius ~1290km). Local Convective Currents in the Mantle At the Core. These plates move in Outer Core different directions and at di fferent speeds from th ose Inner Core of the neighbouring ones. The energy for the above circulations is derived from the heat produced from the incessant decay of radioactive elements in the Eurasian North American rocks throughout the Earth’s interior. while the Crust consists of light materials (e. this is in contrast to ~25 C. the heavier and denser materials sank to the center and the lighter ones rose to the top. along the same direction or in opposite directions. The convective flows of Mantle material cause the Crust and some portion of the Mantle. These three types of inter-plate interactions are the convergent. divergent and transform boundaries (Figure 4). On the other hand. the pressure ~4 million atmospheres and density ~13.g. The Outer Core is Figure 2: liquid in form and the Mantle has the ability to flow. African Amer ican part of the Mantle. nickel and iron). These convection Plate Plate currents result in a circulation of the earth’s mass. 1 . Mantle. Figure 1 shows these layers. on an average. then. because of prevailing high temperature and The relative movement of these plate boundaries pressure gradients between the Crust and the Core. the plate in the front is slower.5 gm/cc on the surface of the Earth. the plate behind it comes and collides (and m ountains are formed). the Outer Core (thickness ~2200km). the Mantle (thickness ~2900km) and the Crust (thickness ~5 to 40km). only to come out again from Austr alian Plate Plate Plate another location. sometimes two plates move away from one Figure 1: another (and rifts are created). leading to different Figure 3: portions of the Earth undergoing different directi ons Maj or Tectonic Plates on the Earth’s surface of movements along the surface. and slowly as the Earth cooled down. Sometimes. respectively. Many such local circulations are taking place at different regions Antarctic Plate underneath the Earth’s surface. beaker (Figure 2). basalts and granites).. a large collection of material masses coalesced to form the Earth. two Inside the Earth plates move side-by-side. The mass absorbed eventually melts Plate South under high temperature and pressure and becomes a Indo. The convergent The Circulations Convection currents develop in the viscous boundary has a peculiarity (like at the Himalayas) that sometimes neither of the colliding plates wants to sink.g. India Energ y Strength Build-Up Sponsored by: B Energ y Release Building Materials and Technology Promotion Council. Vis it www. when the generated at the fault during earthquakes is along both rocks along a weak region in the Earth’s Crust reach vertical and horizontal directions (called Dip Slip) and their strength. with (Figure 5). I t may be reproduced without ch anging its conten ts (years) and with du e ackno wled gemen t.A. a violent shaking of the Earth when large elastic strain energy released spreads out through seismic waves that travel through the body and along the surface of the Earth.gov/neis/general/handouts/ Elastic Stress Cumulative Slip EQ C general_seism icity..usgs.. Fourth Edition. the process of strain build-up at this modi fied interface between the rocks starts all over again (Figure 6). But.htm B A Authored by: A C.usgs. after the earthquake is over.gov/kids/quake.Murty C Time Indian Institute of Technology Kanpur (years) Kanpur. W.B. the energy released during the 2001 Bhuj (India) earthquake is about 400 times (or more) that released by the 1945 Atom Bomb dropped on Hiroshima!! Dip Slip Faults Strike Slip Faults Stage A Stage B Slip Figure 5: Figure 7: Type of Faults Elastic Strain Build-Up Stage C and Brittle Rupture Reading Material Bolt. a sudden movement takes place there lateral directions (called Strike Slip) (Figure 7). The material points at the fault over which slip occurs usually constitute an oblong three-dimensional Transfor m Boundary volume. opposite sides of the fault (a crack in the one of them dominating sometimes. India A C Time This release is a property of IIT Kanpur and BMTPC New Delhi. 1993 Latur deformations that occur due to the gigantic tectonic (India) earthquake). to see previous IITK-BMTPC Earthquake Tips. New York.R.org or www. Earthquakes. the material Earthquakes. 1897 Assam (India) earthquake).org.nicee. and so elastic A number of earthquakes also occur within the plate strain energy is stored in them during the itself away fr om the plate boundaries (e.IITK-BMTPC Earthquake Tip 1 What Causes Earthquakes? page 2 The sudden slip at the fault causes the earthquake…..g. (1999). Thus.in. Figure 4: Types of Types of Earthquakes and Faults Divergent Boundary Inter-Plate Boundaries Most earthquakes in the world occur along the boundaries of the tectonic plates and are called Inter- The Earthquake plate Earthquakes (e.gov/faq/ EQ http://neic. rocks where movement has taken place) suddenly slip and release the large elastic strain energy stored in the interface rocks. with its long dimension often running into tens of kilometers. For example.ac .bmtpc. USA EQ http://earthquake. In both types of earthquakes. Suggestion s/co mmen ts Figure 6: Elastic Rebound Theory may be sent to: eqtip s@iitk. H. these are called Intra-plate plate acti ons that occur in the Ear th. And.V. Freeman and Company. the slip contained in r ocks is also very brittle.g. April 2002 2 . Earth Convergent Boundary scientists know this as the Elastic Rebound Theory. New Delhi. Rocks are made of elastic material.html Slip http://www.fema. reflecting and refracting at each interface. For example. P. The principle on which it works Love waves cause maximum damage to structures by is simple and is expli citly reflected in the early their racking motion on the surface in both vertical seismograph (Figure 3) – a pen attached at the tip of an and horizontal direction s. S-waves do not travel a seismograph.8 km/sec and The instrument that measures earthquake shaking. Shaking is more severe (about twice as much) at amplitude of oscillations. pen and chart paper constitute the recorder. and surface waves consist of Love waves and Up and down Rayleigh waves. The pendulum mass. Sideways in horizontal p lane Structure Surface W aves Rayleigh Waves Elliptic in vertical plane Soil Body W aves Fault EQ Rupture Figure 2: Geologic Strata Motions caused by Body and Surface Waves (Adapted from FEMA 99. in granites. the often the basis for designing structures buried drum. S-waves in associati on with e ffects of recorder and the timer. ~3. These waves are of two types . string. When P. 3 . material particles undergo extensional and compressi onal strains along direction of energy transmission. A magnet around surface by reflections at di fferent layers of soil and the string provides required damping to control the rock. but under S-waves.body waves and surface waves. forms the timer. Rayleigh wave makes a Direction of material particle oscillate in an elliptic path in the Energy Trans mission vertical plane (with horizontal moti on along direction Love Waves of energy transmission). most of their energy is reflected from a support) marks on a chart paper that is held on back. and underground for smaller levels of acceleration than the motor that rotates the drum at constant speed those above the ground. Non-Technical Figure 1: Arrival of Seismic Waves at a Site Explanation of the NEHRP Recommended Provisions) P-waves are fastest. M easuring Instruments and S-waves have speeds ~4. followed in sequence by S-. the Earth's surface than at substantial depths. the latter are restricted to near the Earth’s surface (Figure 1). Learning 2 Earthquake Design Earthquake Tip and Construction How the ground shakes? Seismic Waves Large strain energy released during an earthquake P-Waves Push and pull travels as seismic waves in all directions through the Earth’s layers. the through liquids. respectively. but Side to side with no vertical component.and S-waves reach oscillating simple pendulum (a mass hung by a string the Earth's surface. has three components – the sensor. This is magnet and support together constitute the sensor.0km/sec. Body waves consist of Extensi on Compressi on Primary Waves (P-waves) and Secondary Waves (S- S-Waves waves). Under P-waves. Love and Rayleigh waves. Some of this energy is returned back to the a drum rotating at a constant speed. oscillate at right angles to it (Figure 2). Love waves cause surface moti ons similar to that by S-waves. e.org or type of slip at fault rupture... measuring vertical oscillations. 0 10 20 30 40 50 60 The analog instruments have evolved over time.. the maximum amplitudes of horizontal consequence of motion s caused by seismic waves motions in the two or thogonal directions are about the generated by energy release at each material point same.. This can happen with earthquakes in C. the vertical time.Murty the vicinity or even with large earthquakes at Indian Institute of Technology Kanpur reasonable medium to large distances. In a rigid structure.B. Earthquakes. Usually. However. However. The Council. from engineering viewpoint. Freeman and earthquakes. Company. Time (sec) but today. They carry distinct information regarding ground shaking. the direction varying randomly with time.6 times the acceleration due to Support Drum gravity) suggests that the movement of the ground can cause a maximum horizontal for ce on a rigid structure equal to 60% of its weight.R. These waves arrive at various instants of horizontal directi on. may be sent to: eqtip s@iitk. The nature of accelerograms may vary and with du e acknowled gemen t.. W. The digital instrument records the ground motion on the memory Figure 4:: of the microprocessor that is in-built in the instrument. velocity or acceleration.5g 1991 Uttarkas hi Earthq uake (Uttarkas hi. the maximum amplitude in the within the three-dimensional volume that ruptures at vertical direction is usually less than that in the the fault.6g (= 0. Peak amplitude (peak ground accelerati on. peak amplitude.nicee. and hence experience the same maximum acceleration of PGA. the drum holding the chart paper does not r otate). India variation of ground acceleration with time recor ded at a point on ground during an earthquake is called an This release is a property of IIT Kanpur and BMTPC New Delhi. Thus. frequency content (e. Fourth Edition. duration of strong shaking.bmtpc.0g were recorded during the 1994 Nor thridge Figure 3: Schematic of Early Seismograph Earthquake in USA. New York. For instance. USA strong motions that can possibly damage structures Authored by: are of interest.in. In contrast. have different amplitudes and carry different design acceleration is taken as 1 2 to 2 3 of the levels of energy. H. all Chart Paper Direction of points in it move with the ground by the same Ground Shaking Rec orded amount. be felt by humans. energy carried by ground shaking at each frequency) are often used to distinguish them. India Characteristics of Strong Ground M otions Sponsored by: The motion of the ground can be described in Building Materials and Technology Promotion terms of displacement. amplitude of String shaking associated with each frequency) and energy Magnet content (i.V. Visit www. Some instruments do not 1940 Imper ial Va lley Earth quak e (El Centro. But.org.g. S00E) have a timer device (i. PGA) i s Pendulum Bob Pen physically intuitive. Such instruments provide only 1971 Sa n Fernan do Earthq uake (Pac oima D am. path from fault rupture to the Earth’s sur face. This makes it possible to locate distant Bolt.e. N75E) technology are more commonly used. for this reason they are called seismoscopes. Of course.A. and May 2002 4 . maximum horizontal and vertical ground accelerations Large earthquakes at great distances can produce in the vicinity of the fault rupture do not seem to have weak motions that may not damage structures or even such a correlation. Suggestion s/co mmen ts (Figure 4) depending on energy released at source. digital instruments using modern computer 0. a horizontal PGA Rotating value of 0.IITK-BMTPC Earthquake Tip 2 How the ground shakes? page 2 local soil (Figure 1). the motion at any site on ground is random in nature with its amplitude and horizontal design acceleration. In design codes. to see previous IITK-BMTPC Earthquake Tips. N90E) (Figure 3) is replaced with a spring pendulum oscillating about a fulcrum.e. sensitive instruments can Resource Material record these. New Delhi. geology along the travel www. Kanpur. the s tring pendulum 1985 Mex ico Earthq uake (SCT 1A. Horizontal PGA values greater than 1. for frequencies in the range 0. strong ground moti ons One such instrument is required in each of the two carry significant energy associated with shaking of orthogonal horizontal directions. Some typical recorded accelerograms Strong Ground M otions Shaking of ground on the Earth’s surface is a net Generally. N76W) the maximum extent (or scope) of moti on during the earthquake.03-30Hz (i. cycles per sec). (1999). I t may be reproduced without ch anging its conten ts accelerogram.ac. magnitude scale. and the ones after are called Aftershocks. These isoseismals. There are many Foreshocks. and changes to natural surroundings. shaking at a locati on during an earthquake.200 (estimated) Focus Minor 3 – 3.0 implies 10 times higher waveform amplitude and about 31 times VII higher energy released. the magnitude of a very small earthquake can be zero or even negative.html Figure 1: Basic terminology Intensity A number of smaller size earthquakes take place Intensity is a qualitative measure of the actual before and after a big earthquake (i. number of earthquakes across the Earth in each of these groups is also shown in the table. Table earthquakes have bigger wave amplitude than those of 2 gives the description of Intensity VIII on MSK Scale.org/nicee/EQReports/Bhuj/isoseisma l. smaller earthquakes. The shaking of the ground en-route and hence damage to depth of focus fr om the epicenter. and is about 1000 ( 31 31) times Source: that released in a M5. Professor Charles Richter scales are based on three features of shaking – noticed that (a) at the same distance. performance of (records of earthquake ground vibration) of larger buildings.nicee. like the Body Wave Magnitude.7 earthquake is about 31 times that released in Earthquake (MSK Intensity) a M6. Most of the energy http::/www. intensity scales. It is obtained from the seismograms and accounts for the dependence of waveform amplitude on epicentral distance. energy released Figure 2: Isoseismal Map of the 2001 Bhuj (India) in a M7. X These numerical magnitude scales have no upper and IX lower limits. Surface Wave Magnitude and Wave Energy Magnitude. and (b) for a given earthquake..9 6. and is Those occurring before the big one are called assigned as Roman Capital Numerals. the Main Shock).3 earthquake is equivalent to that released by the damaging potential of an earthquake. The distribution of intensity at different places seismograms at farther distances have smaller wave during an earthquake is shown graphically using amplitude than those at close distances.7 earthquake.html 5 .9 120 Rupture Moderate 5 – 5. structures. and the point vertically above this on seismic waves that travel to large distances causing the surface of the Earth i s the Epicenter (Figure 1).9 800 Light 4 – 4.usgs. VIII An increase in magnitude (M) by 1. Most of the 1945 Atom Bomb dropped on Hiroshima!!) damaging earthquakes have shallow focus with focal Earthquakes are often classified into di fferent depths less than about 70km. Two commonly used ones are the Modified Mercalli Intensity (MMI) Scale and the MSK M agnitude Scale.gov/neis/eqlists/e qstats. and The point on the fault where slip starts is the Focus only a small fracti on of it (fortunately) goes into the or Hypocenter.0 M2-3: ~1. This scale is also called Local Magnitude scale. the Richter Scale. (Did you know? The energy released by a is an important parameter in determining the M6. called as Focal Depth. Distance from epicenter groups based on their size (Table 1). it indicates that Epicentral Distance on an average one Great Earthquake occurs each year.000/day. seismograms perception by people and animals. The intensity size of the earthquake.e.000 (estimated) Very Minor < 3. Both scales are quite similar and range from I Magnitude is a quantitative measure of the actual (least perceptive) to XII (most severe).9 18 Fault Depth Strong 6 – 6. Annual average to any point of interest is called epicentral distance. Place of Table 1: Global occurrence of earthquakes Epicenter Interest Group Magnitude Annual Average Number Great 8 and higher 1 Focal Major 7 – 7. Learning 3 Earthquake Design Earthquake Tip and Construction What are Magnitude and Intensity? Terminology released goes into heat and fracturing the rocks. For instance. There are other magnitude scales. M1-2: ~8. lines joining places with equal seismic prompted him to propose the now commonly used intensity (Figure 2).7 earthquake.9 49.000/day Source: http::/neic. However.06-0. consider the analogy (50 lumens) of an electric bulb (Figure 3). may be sent to: eqtip s@iitk. H. to see previous IITK-BMTPC Earthquake Tips. Water in lakes becomes turbid.usgs. Grade 2 – Moderate damage.Destruction of Buildings strong ground motion records fr om seismic (a) Fright and panic. The peak ground acceleration (PGA). Type B . from an electric bulb Here.C.30 0. In many cases.Bolt. Many – about 50%. Tombstones (g) Source: B. one can measure the size of an earthquake by the amount of strain energy released by the fault rupture. changes in flow and level ML of an earthquake with the intensity I0 sustained in of water are observed. intensity is an indicator of the severity of shaking generated at a given location.g.org or For instance.IITK-BMTPC Earthquake Tip 3 What are Magnitude and Intensity? page 2 Table 2: Description of shaking intensity VIII as per enclosed by the isoseismal VIII (Figure 2) may have MSK scale experienced a PGA of about 0. (Indian Reprint in 1969 by Eurasia Publishing House Private Limited. (1958).25-0. the M7. Earthquakes. The illumination at a location near a 100-Watt bulb is higher than that Far farther away from it. (20 lumens) measured in lumens) at a location depends on the Figure 3: Reducing illumination w ith distance wattage of the bulb and its distance from the bulb. New Gutenberg and Richter in 1956 provided an reservoirs come into ex istence. Thus.55 >0..03-0.bmtpc. i.50-0. and most bu ildings of T ype A suffer damage of Grade 4. the intensity of light (or illumination. Also.0 earthquake html causes different shaking intensities at different locations.15 0.nicee. June 2002 6 .Well-built structures with the corresponding Arabic numerals..0). Even ground shaking. Most – about 75% IX with 9.04 0. Approximate empirical This release is a property of IIT Kanpur and BMTPC New correlations are available between the MM intensities Delhi. Grade 3 – Heavy damage. (b) Most buildings of Type C suffer damage of Grade 2. New York.V. Freeman and M agnitude and Intensity in Seismic Design Company Inc. Thus. USA. and the damage induced in buildings at Authored by: these locations is different. India of the ground shaking.R. Hanging lamps are damaged in part. during the same earthquake of a certain magnitude. different locations experience different levels of intensity. Most buildin gs of Type B suffer damage of MMI V VI VII VIII IX X Grade 3. W. New Delhi. scientists steep slopes..ac.A. persons driving motorcars are instruments are relied upon to quantify destructive disturbed. the size of the bulb (100-Watt) i s like the magnitude of an earthquake. and n ot so much the Kanpur. Elementary Seismology.ordinary equation.0 earthquake? But.rural constructions. Visit www. This means that the magnitude of the earthquake is a single value for a given earthquake.07 0. during the 2001 Bhuj earthquake.org. Grade 4 – Destruction. the Bright severity of shaking is much higher near the epicenter (100 lumens) than farther away. Suggestion s/co mmen ts and the PGA that may be experienced (e.30g.. There are several different relations Grade 1 Damage – Slight damage. cracks develop in ground up to widths of several centimeters. and Table 3: PGAs during shaking of different intensities few of Grade 3. (c) Small landslips occur in hollows and on banked roads on Based on data fr om past earthquakes.60 Memorials and monuments move and twist. Here and there branches of trees break off. New Delhi) One often asks: Can my building withstand a http://neic. Table 3). 1993 overturn. e. I t may be reproduced without ch anging its conten ts and with du e acknowled gemen t.e. the area www. earthquake-resistant design. These are critical for cost-e ffective heavy furniture moves and partly overturns. Stonewalls collapse. Type C .Freeman and Co.25-0. Few – about 5%.F. Sponsored by: maximum acceleration experienced by the ground Building Materials and Technology Promotion during shaking.in. proposed by other scientists.Murty levels of intensity of shaking that buildings and Indian Institute of Technology Kanpur structures are designed to resist. Note: the epicentral area as: ML 2 3 I0 + 1.. Normal To elaborate this distinction. is one way of quantifying the severity Council. indeed it is particular C. intensity Single. Richter.gov/neis/general/handouts/magnitude_intensity.H. now Intensity VIII . Grade 5 – Total damage Basic Difference: M agnitude versus Intensity 100 Watt Bulb Magnitude of an earthquake is a measure of its size.g. Clearly. Occasional brea king of pipe seams occurs. For instance. W. magnitude 7. On Near the other hand. Dry wells refill and existing approximate correlati on between the Local Magnitude wells become dr y. San Francisco. PGA 0. (For using this Type A structures . While the bulb releases 100 Watts Dull of energy. the Roman numbers of intensity are replaced masonry constructions.10-0. and the illumination at a Resource Material location like the intensity of shaking at that location. India magnitude. The the intensity scale from I-X to I-XII. but also allowed us to learn about over long geological time in the Tethys. but large amounts of shortening and thickening takes a number of earthquakes have also occurred in the place. Erosion has exposed the roots of the old the type of damage sustained led to improvements in mountains and removed most of the topography. a marine deposits testi fying to submergence under the major porti on of the Indian Ocean and other smaller sea millions of years ago. Most earthquakes occur along the Himalayan remain close to the surface. The earthquake (M7. A sea. another is called subduction. lava flowed earthquake in which many structures went afloat. like at the Himalayas and the Tibet. Coastal areas like Kachchh show Australian Plate. Before the Himalayan collision. Tethys. but are softened by weathering liquefaction of the ground took place over a length of near the surface. Each of these Himalayas consist primarily of sediments accumulated caused disasters. Gangetic basin with deep alluvium is a great For instance. 300km (called the Slump Belt) during 1934 Bihar-Nepal several tens of millions of years ago. this process of one tectonic plate getting under and around India over the past century (Figure 2). 7 . separated Some of these occurred in populated and urbanized these plates before they collided. The former can undergo surface or in relatively un-inhabited places. the plains of the of 53 years from 1897 to 1950. collisions. plate boundary (these are inter-plate earthquakes). When continents converge. The peninsular part of the country consists 100km (called Allah Bund). 1819 Cutch Earthquake produced an depression caused by the load of the Himalayas on the unprecedented ~3m high uplift of the ground over continent. but the latter is buoyant and so tends to Table 1. peninsular region (these are intra-plate earthquakes). The Indo. Learning 4 Earthquake Design Earthquake Tip and Construction Where are the Seismic Zones in India? Basic Geography and Tectonic Features across the central part of peninsular India leaving India lies at the northwestern end of the Indo. the Earth’s Crust. the January 2001 Bhuj Ganges and other rivers. and the peninsula. Eurasian Plate Himalayas Indo- Gangetic Plains Nar mada Plains Mahanadi Plains Deccan Godavari Shield Plains <5 Arabian Sea Peninsular Bay of Bengal 5<6 India 6<7 7<8 Indo-Australian Plate >8 Figure 1: Geographical Layout and Tectonic Plate Boundaries at India Figure 2: Some Past Earthquakes Three chief tectonic sub-regions of India are the Four Great earthquakes (M>8) occurred in a span mighty Himalayas along the north. The 1897 Assam Earthquake of ancient rocks deformed in the past Himalayan-like caused severe damage up to 500km radial distances. This plate is colliding against the huge Prominent Past Earthquakes in India Eurasian Plate (Figure 1) and going under the Eurasian A number of significant earthquakes occurred in Plate. countries. Many went lithosphere. Part of the areas and hence caused great damage. Some of subduction at great depths when it converges against the damaging and recent earthquakes are listed in another plate.7) is almost as large. layers of basalt rock. as they occurred deep under the Earth’s and the rest by the continents. Extensive rocks are very hard. Australia. earthquakes and to advance earthquake engineering. which encompasses India. is covered by oceans unnoticed. bmtpc. 15 Jan.000 zone map in the peninsular region has been modified. local soil profile.R. This release is a property of IIT Kanpur and BMTPC New Delhi. (1997). (1984).3 VIII 1. Therefore. projects. 1999 Chamoli 12:35 6.7 X 13.004 20 Oct. Based on the levels of intensities sustained during damaging past earthquakes. The map has been revised Max. 1993 Killari (Latur) 03:53 6. Parts of Himalayan variations in soil type and geology cannot be boundary in the north and northeast. The Indian Standards provided the first may be sent to: eqtip s@iitk. VI.0 X Nil merged with those of seismic zone II. VIII. Building Materials and Technology Prom otion Council. 1934 Bihar-Nepal 14:13 8.6 VIII 63 26 Jan. Suggestion s/co mmen ts country. et al. III.530 seismic zone map is not the final word on the seismic 21 Jul. Geological Survey of India. Also. and the Kachchh represented at that scale. when most of the population is indoors.0 IX 115 hazard of the country.6 IX 1. which was later revised in www. for impor tant area in the west were classified as zone V. (2000). July 2002.000 zone II in the 1970 version of the map. to see previous IITK-BMTPC Earthquake Tips. New Delhi.0 VIII 38 29 Mar. Revised Aug ust 2004 8 . II.. 1950 Assam 19:31 8. VII. IV and V.V. Also.4 X 11. 1956 Anjar 21:02 7.6 IX 768 30 Sep. 1988 Bihar-Nepal 04:39 6.in. 1967 Koyna 04:30 6. Seismotectonic Atlas of Indian and its Environs. IV and V (Figure 3).7 XII 1. Dasgupta. Casualties are expected to be high for earthquakes that strike during cold winter nights. scale view of the seismic zones in the country.6 X 30. Thus. IS:1893. Vulnerability Atlas of India. 1900 Coimbatore 03:11 6. the seismic hazard is evaluated specifi cally for that site. Bureau of Indian Standards. Seismic Zones of India The varying geology at different locations in the country implies that the likelihood of damaging earthquakes taking place at different locations is different.5 VIII 200 23 Mar.5 X 1. 1905 Kangra 06:20 8. India Sponsored by: Figure 3: Indian Seismic Zone Map of 1970 Building Materials and Technology Promotion Council. etc.000 Madras now comes in seismic zone III as against in 31 May 1935 Quetta 03:03 7. I t may be reproduced without ch anging its conten ts the seismotectonics and the seismic activity in the and with du e acknowled gemen t. 21 Aug. respectively. Ministry of Ur ban Development. Authored by: C.500 seismic zone I in the 1970 version of the map are 8 Feb. for the purposes of urban planning. The maximum Modified Mercalli (MM) intensity of seismic shaking The national Seismic Zone Map presents a large- expected in these zones were V or less.4 IX 7. Resource Material BMTPC.928 22 May 1997 Jabalpur 04:22 6. This 2002 15 Aug.Murty Indian Institute of Technology Kanpur Kanpur. 1991 Uttarkashi 02:53 6.S. a seismic zone map is required to identify these regions. Seismic microzonation accoun ts for local variations in geology. and hence there can be no sense 10 Dec. III. such as a major dam or a nuclear power plant.6 X 19. the seismic 4 Apr. and it now has only four Date Event Time Magnitude Deaths Intensity seismic zones – II. New Delhi. Government of India.IITK-BMTPC Earthquake Tip 4 Where are the Seismic Zones in India? page 2 Table 1: Some Past Earthquakes in India 1967 and again in 1970. 1970 Bharuch 20:56 5. 2001 Bhuj 08:46 7.500 12 June 1897 Assam 17:11 8.org. Local and IX and higher.805 The timing of the earthquake during the day and during the year critically determines the number of casualties.nicee.. New Delhi. the 1970 Figure 4: Indian Seismic Zone Map as per version of the zone map subdivided India into five IS:1893 (Part 1)-2002 zones – I. metropolitan areas are microzoned. India The seismic zone maps are revised from time to time as more understanding is gained on the geology.ac. Indian Standard Criteria for Earthquake Resistant Design of Structures. The areas falling in 16 June 1819 Cutch 11:00 8. again in 2002 (Figure 4).org or seismic zone map in 1962.4 VII 30 of complacency in this regard. Visit www. These for ces generated in the called the gravity load. causing downward directi on (-Z). Learning 5 Earthquake Design Earthquake Tip and Construction What are the Seismic Effects on Structures? Inertia Forces in Structures would like to come back to the straight vertical Earthquake causes shaking of the ground. these internal forces in the columns are called but your upper body tends to stay back making you fall stiffness forces. columns against vertical shaking. more mass Y and Z directions. This is much like the force in columns. the columns undergo acceleration due to gravity. lighter buildings designed to carry the gravity loads. your feet move with the bus. even Horizontal and Vertical Shaking the building is thrown backwards. between its ends. The downward for ce Mg is forces in columns. called inertia force.e. columns resist deformations. The vertical acceleration during columns can also be understood in another way. 9 . used in the design of structures to resist the gravity this movement is shown as quantity u between the loads. and the roof Earthquake causes shaking of the ground in all experiences a force. when the ground moves. situation that you are faced with when the bus you are bigger is the column size). Also. they develop internal forces. But is the relative horizontal displacement u between the since the walls and columns are connected to it. larger is this for ce. say) (Figure Newton’s Second Law of Motion. they are sustain the earthquake shaking better. the inertia force F I is 3).. The larger roof has a tendency to stay in its original position. In fact. usually most structures tend to be adequate roof and the ground. ground shaking either adds to or subtracts fr om the During earthquake shaking. If the roof has a three directions – along the two horizontal directi ons mass M and experiences an acceleration a. reason. since the walls or columns are flexible. during the earthquake.e. given a free option.e. you are a building thrown backwards as if someone has applied a force on the upper body. the stiffness force in a column is backwards!! This tendency to continue to remain in the the column stiffness times the relative displacement previous position is known as inertia. then from (X and Y. Similarly. i. In the building. From Newton’s First Law of Motion. In Figure 2.. Also. But. they top and bottom of the column. when the base of the building moves with the ground. the columns carry no base. All structures are primarily means higher inertia force. But. and its direction is randomly back and forth (. the motion of Inertia Force the roof is different from that of the ground (Figure 1). even though horizontal earthquake force through them. the ground shakes mass M times acceleration a. i.. u Roof Column Foundation Figure 1: Effect of Inertia in a building w hen shaken at its base Soil Acceleration Consider a building whose roof is supported on columns (Figure 2). For this standing in suddenly starts. designed for a force equal to the mass M (this includes Effect of Deformations in Structures mass due to own weight and imposed loads) times the The inertia force experienced by the roof is acceleration due to gravity g acting in the vertical transferred to the ground via the columns. the forced to bend. In the building resting on it will experience motion at its straight vertical position. So a position. Coming back to the analogy of Figure 2: Inertia force and relativ e motion w ithin yourself on the bus: when the bus suddenly starts. Clearly. the stiffer the columns are (i. Therefore. say). and the vertical direction (Z. the larger this internal drag the roof along with them. opposite to that of the acceleration. Since factors of safety are relative movement between their ends.and +) along each of these X. may not be able to safely sustain the effects of horizontal earthquake shaking. Indian Institute of Technology Kanpur Kanpur. I t may be reproduced without ch anging its conten ts made of brittle material like masonry. walls. Failures of masonry walls August 2002 10 . Foundations Resource Material Chopra. to the foundations. Walls are relatively thin and often Delhi. They are poor in and with du e acknowled gemen t.A.Murty all structural components. in general.V. Similarly. USA. Structures designed for gravity loads. Figure 5a). Figure 3: Principal directions of a building However. floor slabs and beams receive more care Council. But. IITK-BMTPC Earthquake Tip 5 What are the Seismic Effects on Structures? page 2 have been observed in many earthquakes in the past Z (e. and finally to the soil system underneath (Figure 4). India Walls or columns are the most cri tical elements in Sponsored by: transferring the inertia forces.. Dynamics of Str uctures . New Delhi. than This release is a property of IIT Kanpur and BMTPC New walls and columns. EERI Monograph. in traditional Building Materials and Technology Promotion construction. Flow of Inertia Forces to Foundations Under horizontal shaking of the ground.K. columns.nicee. (1980). it is necessary to ensure adequacy of the structures against horizontal earthquake effects. India and attention during design and construction. and foundations) and the connections between them must be designed to safely transfer these inertia forces through them.org. horizontal shaking along X and Y directions (both + and – directions of each) remains a concern. Inertia F orces Floor Slab (b) Collapse of reinforced concrete columns (and W alls building) during 2001 Bhuj (India) earthquake and/or Columns d i 1991 Utt k hi (I di ) E th k Figure 5: Importance of designing walls/columns for horizontal earthquake forces.A Primer.R. Visit www.ac. So.in. each of these structural elements (floor slabs.bmtpc.g. The failure of the ground storey columns resulted in numerous building collapses during the X 2001 Bhuj (India) earthquake (Figure 5b).org or carrying horizontal earthquake inertia forces along the www. direction of their thickness. poorly designed and constructed reinforced con crete columns can be Y disastrous. Next Upcoming Tip Soil What is the Influence of Architectural Features on Earthquake Behaviour of Buildings? Earthquak e Shaki ng Authored by: Figure 4: Flow of seismic inertia forces through C. Earthquake Engineering Research Institute. These lateral inertia forces are transferred by the floor slab to the walls or columns.. Hence. horizontal inertia for ces are generated at level of the (a) Partial collapse of stone masonry walls mass of the structure (usually situated at the floor during 1991 Uttarkashi (India) earthquake levels). Suggestion s/co mmen ts may be sent to: eqtip s@iitk. to see previous IITK-BMTPC Earthquake Tips. and in other occa sions both shape and structural system work together (a) Simple Plan to make the structure a marvel. if earthquake shaking. Size of Buildings: In tall buildings with large (b) Corners height-to-base size ratio (Figure 1a). have sustained itself. Hence. tend to damage or collapse which i s initiated in 11 . any deviation or discontinuity in this load transfer path results in poor performance of the building. And. The wide range of structural damages observed during past earthquakes across the world is very educative in identifying structural con figurations that are desirable versus those which must be avoided. even a poor engineer cannot harm its 7 on How Buildings Twist During Earthquakes? ultimate performance too much. A discussion in this aspect will be we start-off with a good configuration and reasonable presented in the upcoming IITK-BMTPC Earthquake Tip framing system. avoided by making the buildings in two parts. Sometimes the shape of the building catches the eye of the visitor. architects and structural engineers must work significant damage. in buildings with large plan area like into simple plans warehouses (Figure 1c). Vertical Layout of Buildings: The earthquake forces developed at different floor levels in a building (b) too long need to be brought down along the height to the ground by the shortest path. each of these ::good choices of shapes and structure has significant bearing on the performance of the building during strong earthquakes. In short but very long buildings (Figure 1b).” Architectural Features A desire to create an aesthetic and fun ctionally efficient structure drives archite cts to con ceive wonderful and imaginative structures. all the columns/walls are not equally distributed in plan. the bad effects of together to ensure that the unfavourable features are these interior corners in the plan of buildings are avoided and a good building configuration is chosen. the horizontal seismic for ces Figure 2: Simple plan shape buildings do well can be excessive to be carried by columns and walls. do not perform well during earthquakes. sometimes the structural system appeals. V. the plan is simple. as: junction (Figure 2c). geometry. 3b). the (c) Separation jo ints make complex plans damaging effects during earthquake shaking are many. engineer can do is to provide a band-aid . Buildings that have fewer columns or walls in a much larger or much smaller than the other particular storey or with unusually tall storey (Figure tw o. Learning 6 Earthquake Design Earthquake Tip and Construction How Architectural Features Affect Buildings During Earthquakes? Importance of Architectural Features Horizontal Layout of Buildings: In general. a rectangular plan shapes using a separation joint at the noted Earthquake Engineer of USA. Buildings with vertical setbacks (like the hotel buildings with a few storeys wider than the rest) cause a sudden jump in (a) too tall (c) too large in plan earthquake forces at the level of discontinuity (Figure Figure 1: Buildings w ith one of their ov erall sizes 3a). For The importance of the configuration of a building example. size and have performed well during strong earthquakes. Often. an L-shaped plan can be broken up into two was aptly summarised by Late Henry Degenkolb.improve a Buildings with such features tend to twist during basically poor solution as best as he can. Many times. at the planning stage and + shaped in plan (Figure 2b). but the “If we have a poor configuration to start with. H carried to the ground. Conversely. during earthquakes. like those U. the horizontal and Curves movement of the floors during ground shaking is :: poor large. in addition to how the earthquake forces are Buildings with re-entrant corners. However. The behaviour of a building during earthquakes buildings with simple geometry in plan (Figure 2a) depends critically on its overall shape. EARTHQUAKES An Architect’s Guide to Non- Structural Se ismic Hazard. which cause s ill effects like building heights do not match (Figure 4). in which these walls do not go all the way to the ground but stop at an upper level. I t may be reproduced without ch anging its conten ts Figure 3: Sudden deviations in load transfer path and with du e acknowled gemen t. of course. www. John Wiley. have discontinuities in the load transfer path (Figure 3d).. US A.bmtpc. to see previous IITK-BMTPC Earthquake Tips. If not. With increase in building Buildings on slopy ground have unequal height height. they must be minimised.J. this can be very an intermediate storey and do not go all the way to the dangerous. one will continue to make buildings interesting rather than monotonous. foundation. Figure 4: Pounding can occur between adj oining buildings due to horizontal v ibrations of the tw o buildings. Building Config uration and Seismic Desig n. than accurate determination of code specified design forces.in. this collision can be a greater problem.nicee. New Delhi. Some buildings have reinforced concrete walls to carry the earthquake loads to the foundation. the roof of twisting and damage in shorter columns (Figure 3c).org. USA. John Wiley & Sons.. Suggestion s/co mmen ts along the height lead to poor performance of may be sent to: eqtip s@iitk. Inc. this need not be done at the cost of poor Unusually behaviour and earthquake safety of buildings. When irregular features are included in buildings.Murty Discontinued i n Indian Institute of Technology Kanpur Ground Storey Kanpur. and Reitherman. Many buildings with an open ground Adjacency of Buildings: When two buildings are storey intended for parking collapsed or were severely too close to each other. India (e) Discontinuing Structural Members This release is a property of IIT Kanpur and BMTPC New Delhi.org or buildings.H. Next Upcoming Tip How Buildings Twist During Earthquake s? Reinforced Authored by: Concrete Wall C. or are known to have made greater difference.R.. (c) Slopy Ground (d) Hanging or Floating Columns Lagorio.C. Tall Architectural features that are detrimental to Storey earthquake response of buildings should be avoided. Visit www. Resource Material Arnold. September 2002 12 .R. When columns along the slope. India Sponsored by: Building Materials and Technology Promotion Council.ac. Buildings. (a) Setbacks Building Design and Codes… Looking ahead.V. (1982). they may pound on each other damaged in Gujarat during the 2001 Bhuj earthquake. a considerably higher level (b) Weak or Flexible Storey of engineering effort is required in the structural design and yet the building may not be as good as one with simple architectural features. the shorter building may pound at the mid-height of Buildings with columns that hang or float on beams at the column of the taller one. Decisions made at the planning stage on building configuration are m ore important.IITK-BMTPC Earthquake Tip 6 How Architectural Features Affect Buildings Dur ing Earthquakes? page 2 that storey. during strong shaking. are liable to get severely damaged during earthquakes. However. (1990). This building moves such that its floors displace horizon tally as well as rotate. a building with identical Heav y Sid e Earthquak e vertical members and that are uniformly placed in the Ground Shaking of Building two horizontal directions. swings back and forth such that all uniformly in plan of building. 13 . Buildings vibrate back and forth during earthquakes. Buildings with more than Figure 2: Identical vertical members placed one storey are like rope swings wi th more than one uniformly in plan of building cause all points cradle. just that they are inverted swings (Figure 1). Again.e. both sw ing Light Side back-and-forth w hen shaken horizontally. if the mass on the floor of a building is more on one side (for instance. when you sit in the middle of the cradle. The more modern versions of these swings can be seen today in the children’s parks in urban areas. they have a plastic cradle tied with steel chains to a steel framework. on the floor to move by same amount. if you see from sky. w hile the latter are raised from the ground. it twists (i. Twist (a) Single-storey building (b) Three-storey building Figure 1: Rope sw ings and buildings. Learning 7 Earthquake Design Earthquake Tip and Construction How Buildings Twist During Earthquakes? Why a Building Twists Uniform Movement In your childhood. Thus. amount in the direction in which it is shaken (Figure 2). It swings equally.a wooden cradle tied with coir ropes to the sturdy branch of an old tree. more mass on points on the fl oor move horizontally by the same one side causes the floors to twist. Likewise. let us go back to the rope swings on the tree: if you sit at one end of the cradle. Buildings too are like these rope Earthquake swings. when shaken at its base in a Figure 3: Even if v ertical members are placed certain direction. then that side of the building moves more under ground movement (Figure 3). moves more on the side you are sitting). Identical Vertical Ground The vertical walls and columns are like the ropes. one side of a building may have a storage or a library). and Members Movement the floor is like the cradle. This also happens sometimes when more of your friends bunch together and sit on one side of the swing. Consider a rope swing that is tied identically with two equal ropes. you must have sat on a r ope of Floor swing .. The of Building former are hung from the top. Similarly. EARTHQUAKES An Architect’s Guide to Non- Structural Se ismic Hazard. India twist under earthquake shaking.H.Murty Figure 4: Buildings have unequal vertical Indian Institute of Technology Kanpur members.IITK-BMTPC Earthquake Tip 7 How Buildings Twist During Earthquakes? page 2 Once more. the Delhi.bmtpc.. This time let the two ropes with which the cradle is tied to the branch of the tree be different in length. Likewise.. in buildings with unequal vertical members (i. This induces more damage in the columns and walls on the side that moves more (Figure 6). the Indian seismic code (IS 1893. special calculati ons need to (a) Swing with unequal ropes be done to account for this additi onal shear forces in the design of buildings. twist when shaken at the ground level tw ists during earthquake shaking. Suggestion s/co mmen ts columns under it. Sponsored by: Building Materials and Technology Promotion Buildings that are irregular shapes in plan tend to Council.e. John Wiley & Sons. Building Config uration and W all Seismic Desig n.org or www. horizontally. Resource Material Arnold. John Wiley. What Twist does to Building M embers Twist in buildings. buildings.. I t may be reproduced without ch anging its conten ts overhanging portion swings on the relatively slender and with du e acknowled gemen t. Such a swing also twists even if you sit in the middle (Figure 4a). buildings with twist will perform poorly which building twists during strong earthquake shaking.J. It is best to minimize (if not completely avoid) this twist by ensuring that buildings have symmetry in plan (i. US A.nicee.in.R. W all Next Upcoming Tip What is the Seismic Design Philosophy for Build ings? Columns Columns Authored by: (c) Buildings with walls on two/one sides (in plan) C. The floors twist and displace may be sent to: eqtip s@iitk.. Vertical Axis about for sure. (Figure 4c). USA.C. to see previous IITK-BMTPC Earthquake Tips.R. October 2002 14 .. Visit www. called torsion by engineers. New Delhi. Lagorio. let us consider the rope swing on the tree. If this twist cannot be avoided. and Reitherman.e. in a This release is a property of IIT Kanpur and BMTPC New propped overhanging building (Figure 5). Earthquake Earthquake Ground Ground Movement Movement (b) Building on slopy ground These columns are more vulnerable Figure 6: Vertical members of buildings that move W all more horizontally sustain more damage. makes different portions at the same floor level to move horizontally by different amoun ts. uniformly distributed mass and uniformly placed vertical members). (1982). Many buildings have been severely affected by this excessive torsi onal behaviour during past earthquakes. columns and/or walls) also the Earthquake floors twist about a vertical axis (Figure 4b) and Ground displace horizontally.org. Inc.ac. But. For example. which have Shaking walls only on two sides (or one side) and thin columns Figure 5: One-side open ground storey building along the other. they cause the building to tw ist Kanpur. 2002) has provisions for such calculations. India about a vertical axis. (1990).V. and thereby a disaster role in post-earthquake activities and must remain is avoided. after moderate shaking. the main controlling the damage to acceptable levels at a reasonable members may sustain repairable damage. after a strong earthquake. So. And. like hospitals and fire stations. shaking.0-5.9 occur in the world while the number is only about 18 for magnitude range 7. the may become dysfunctional for further use. safety of pe ople and contents is assured in buildings. which itself (a) Under minor but frequent shaking. although they may get damaged severely but The consequences of damage have to be kept in would not collapse during the strong earthquake. however for still higher level of earthquake motion. while the cost. nuclear power plants) should be designed horizontal forces should n ot be damaged.org). the former intensities of earthquake shaking – seeking approach can lead to a major disaster. Damage in Buildings: Unavoidable Design of buildings to resist earthquakes involves (b) Under moderate but occasi onal shaking. For instance.nicee. engineers designing earthquake. Hence. Therefore. and earthquake-resistant buildings recognize that some (c) Under strong but rare shaking. important Thus. dams (and members of the building that carry vertical and similarly. during an earthquake can be minor. But. These codes throughout the world. This is a major objective of seismic design functional immediately after the earthquake. the main can be a secondary disaster. should we design and construct a building to resist that rare earthquake shaking that may come only once in 500 years or even once in 2000 years at the chosen pr oject Moderate Shaking site. a conflict arises: Should we do away wi th the design of buildings for Strong Shaking earthquake effects? Or should we design the buildings to be “earthquake proof” wherein there is no damage during the Figure 1: Performance objectives under different strong but rare earthquake shaking? Clearly. and the second low repairable damage under minor shaking and approach is too expensive. Contrary to the common thinking that any crack other parts of the building may be damaged such in the building after an earthquake means the building that they may even have to be replaced after the is unsafe for habitation. philosophy should lie somewhere in between these two extremes. even though the life of the building itself may be only 50 or 100 years? Since it costs money to provide additional earthquake safety in buildings. such buildings resist the effects of ground recovered. moderate shaking occasionally and strong shaking rarely.0-7. after minor shaking. building parts that do not carry load may sustain repairable damage. the building will be fully operational within a short time and the repair Earthquake-Resistant Buildings costs will be small. view in the design philosophy. Collapse of dams during earthquakes can summarized as follows (Figure 1): cause flooding in the downstream reaches. Learning 8 Earthquake Design Earthquake Tip and Construction What is the Seismic Design Philosophy for Buildings? The Earthquake Problem may sustain severe (even irreparable) damage. structures must sustain very little damage and should Earthquake Design Philosophy be designed for a higher level of earthquake The earthquake design philosophy may be protecti on. the main members 15 . Relatively speaking. moderate and strong. the design collapse-prevention under strong shaking. minor shaking occurs frequently. such buildings will be completed. play a critical earthquake-resistant buildings. Instead. on average annually about 800 earthquakes of magnitude 5. the The engineers do not attempt to make earthquake- building will be operational once the repair and proof buildings that will not get damaged even during strengthening of the damaged main members is the rare but strong earthquake. the building too r obust and also too expensive.9 (see Table 1 of IITK-BMTPC Minor Shaking Earthquake Tip 03 at www. For example. Thus. but will engineering intention is to make buildings earthquake- stand so that people can be evacuated and property resistant. but Severity of ground shaking at a given location the building should not collapse. J. damage and desirable building behaviour during Next Upcoming Tip earthquakes. you column Figure 3: Ductile and brittle structures – seismic sacrifice some small parts of the electrical circuit. I t may be reproduced without ch anging its conten ts during an earthquake. as ductility. but diagonal cracks running through the columns are not (Figure 2). to save the building from collapsing.V. India allows steel pins to bend back-and-forth by large Sponsored by: amounts.D. New Delhi. Visit www. Yes… a chalk C. Collapse Horizontal Movement of Roof of Building relative to its base (a) Building performances during earthquakes: tw o extremes – the ductile and the brittle. Naeim. in a reinfor ced Total Horizontal Earthquake For ce concrete frame building with masonry filler walls Ductile between columns. called design attempts to avoid structures of the latter fuses. USA Figure 2: Diagonal cracks in columns jeopardize Photo from: Housner & Jennings. especially so in earthquake-resistant design strives to predetermine concrete and masonry buildings) occur in buildings the locations where damage takes place and then to during earthquakes. Earthquake Design Criteria. To do this. Building Materials and Technology Promotion Earthquake-resistant buildings. New York. Inc. (1999).ac. let us first understand how How to make buildings ductile for good seism ic performance? different materials behave. and Vergun. chalk is a brittle material. (2001).Murty breaks easily!! On the contrary..org. particularly their Council.IITK-BMTPC Earthquake Tip 8 What is the Seismic Design Philosophy for Buildings? page 2 damage is unavoidable.in. Engineers define the property that Kanpur. USA. the task now is to identify acceptable forms of & Sons.. these fuses are easily replaced after the electrical over- current.. you need to allow some pre-determined parts to Resource Material undergo the acceptable type and level of damage. Likewise. vertical load carrying capacity of buildings - unacceptable damage. This release is a property of IIT Kanpur and BMTPC New Such buildings have the ability to sway back-and-forth Delhi. Thus. John Wiley So. on Building In general. India main elements.. Boston.nicee. qualified technical professionals are knowledgeable of the causes and severity of damage Brittle in earthquake-resistant buildings.bmtpc. Kluwer Academic Acceptable Damage: Ductility Publishers. Ambrose. Suggestion s/co mmen ts may be sent to: eqtip s@iitk. and also that they occur at the right places and in right amounts. The Seismic Desig n Handbook. Different types of damage factor s affe cting the building performance. (Figure 3). to see previous IITK-BMTPC Earthquake Tips. the cracks between vertical columns Performance and masonry filler walls are acceptable. need to be built with ductility in them. Ductility is one of the most important November 2002 16 . ductile behaviour of the building. For instance. but without collapse www. This approach of earthquake-resistant design is much like the use of electrical fuses in houses: to protect the (b) Brittle failure of a reinforced concrete entire electrical wiring and appliances in the house.F. EERI. Consider white chalk used to write on blackboards and steel pins with solid heads Authored by: used to h old sheets of paper together. and to withstand earthquake and with du e acknowled gemen t..R. Design for Earthquakes.org or effects with some damage. Earthquake-resistant design is therefore concerned about ensuring that the damages in buildings during earthquakes are of the acceptable variety. a steel pin allows it to be Indian Institute of Technology Kanpur bent back-and-forth. while others are not. Some of these cracks are provide good detailing at these location s to ensure acceptable (in terms of both their size and location). kind. Ed. (mainly visualized though cracks. it is being replaced with steel reaching its strength in tension before concrete cement mortar. Figure 2: Tension Test on Materials – ductile This important pr operty of ductility enables steel bars versus brittle materials. Maxi mum Force F Strong Weak Brittle Material Bar Force F Final Elongation is small Figure 1: Masonry is strong in compression but weak in tension. but again its behaviour in tension is poor. The amount and location of steel in a member areas. providing too much steel in RC buildings can be harmful even!! Compression Tension Capacity Design Concept Let us take two bars of same length and cross- sectional area . pulling apart) (Figure 1). pull these two bars Crack until they break!! You will notice that the ductile bar elongates by a large amount before it breaks. contrary to common thinking. Amongst the materials used in building construction. and fail suddenly. steel is ductile. Therefore. Now. most non-urban buildings are made in reinforcement bars. cement Maxi mum Force and water mixed in appropriate proporti ons. This composite material is called masonry. pressing together). More over. Cement concrete is made of crushed stone pieces (called aggregate). Masonry can carry loads that cause reaches its strength in compression. failure where concrete fails first in compression.. Reinforcing steel can carry both tensile and compressive loads. too much and too is large little water. and hence is preferred over a load that causes tension (i. while masonry and concrete are brittle. In general. to undergo large elongation before breaking.one made of a ductile material and another of a brittle material.e. Concrete is much stronger than masonry under compressive Bar Force F loads.. The Ductile properties of concrete critically depend on the amount Final Material Elongation of water used in making concrete. In the plains. while the brittle bar breaks suddenly on reaching its maximum strength at a relatively small elongation (Figure 2). 17 . in recent times. masonry is generally made of reinforced cement concrete or simply reinforced concrete burnt clay bricks and cement mortar. both can cause havoc. both masonry and concrete are brittle. 0 Elongation of Bar Concrete is another material that has been popularly used in building construction particularly F over the last four decades. but.e. Learning 9 Earthquake Design Earthquake Tip and Construction How to Make Buildings Ductile for Good Seismic Performance? Construction M aterials Concrete is used in buildings along with steel In India. steel is a ductile material. sand. in hilly (RC). This type of compression (i. However. stone masonry with mud mortar is more should be such that the failure of the member is by prevalent. but can hardly take failure is ductile failure. Steel is used in masonry and concrete buildings as 0 reinforcement bars of diameter ranging from 6mm to Elongation of Bar 40mm. and columns to the ground. to see previous IITK-BMTPC Earthquake Tips.ac.e. adherence to prescribed standards of construction materials and constructi on processes is essential in assuring an earthquake-resistant building. How flexibility of build ings affects their earthquake response? Therefore.V.V. December 2002 18 . Indian Institute of Technology Kanpur By using the routine design codes (meant for Kanpur. I t may be reproduced without ch anging its conten ts design code. and on-site residential apartment constructi on .J.in. India improve the ductility of the structure. if we want to have such a ductile Weak-Beam Strong-Beam chain.IITK-BMTPC Earthquake Tip 9 How to Make Buildings Ductile for Good Seismic Performance? page 2 Now. (1992). Instead. and construction methods. Next Upcoming Tip but the failure of a beam causes localized effect. its capacity to take load is less). Regular Earthquake-Resistant Design of Buildings testing of construction materials at qualified Buildings should be designed like the ductile laboratories (at site or away).. For example.M. Therefore. it is better to make beams to be the ductile weak links than columns.nicee. e. the force in each link is the same. Figure 4: Reinforced Concrete Building Design: Original Chain the beams must be the weakest links and not the columns – this can be achieved by appropriately sizing the members and providing correct amount of steel reinforcement in them. USA..the multi-storey evaluation of the technical work are elements of good building made of reinforced concrete. workmanship. designers may Sponsored by: not be able to achieve a ductile structure. The correct building Mazzolani.N. Thus. The seismic inertia forces generated at its Resource Material Paulay. and with du e acknowled gemen t.bmtpc. New Delhi.org or www. IS:13920-1993 for RC structures. Theory and Des ign of Seismic- components need to be made ductile. Now. strict Figure 3: Ductile chain design. Visit www. F. It consists of quality control. let us make a chain with links made of brittle Weak Beam and ductile materials (Figure 3). then the chain will fail suddenly and show small final Strong-Column Weak-Column elongation.g. John Wiley. we have to make the ductile link to be the Design Design weakest link. Brittle Links supervision.. (1996). namely beams and columns.T. horizontal and vertical members. is highly sensitive to the F F quality of constructi on materials.org. and Priestley. As Strong more and more force is applied..Murty method (Figure 4). The failure of a Resistant Steel Frames. if the brittle link is the weak one. Seismic Desig n of Reinforce d floor levels are transferred through the various beams Concrete Build ings and Masonry.. periodic training of chain. E&FN Spon. Each of these links will Weak Column fail just like the bars shown in Figure 2. Since the same for ce F is being transferred through all the links. Such provisi ons This release is a property of IIT Kanpur and BMTPC New are usually put together in the form of a special seismic Delhi. column can affect the stability of the whole building. and Piluso.. Ductile Link do not yield stretches by special care is needed in constructi on to ensure that yielding before the elements meant to be ductile are indeed provided breaking with features that give adequate ductility.F. then the chain will show large final elongation. hold the last link at either end of the chain and apply a force F.. consider the common urban workmen at professional training houses. Similarly. Ductile Link Brittle Links Quality Control in Construction The capacity design concept in earthquake- Loaded Chain resistant design of buildings will fail if the strengths of the brittle links fall below their minimum assured values. Special Building Materials and Technology Promotion design provisions are required to help designers Council.R. The strength of brittle construction materials. eventually the chain Beam Strong will break when the weakest link in it breaks. India design against non-earthquake effects). This method of designing RC Authored by: buildings is called the strong-column weak-beam design C. Suggestion s/co mmen ts These codes also ensure that adequate ductility is may be sent to: eqtip s@iitk. provided in the members where damage is expected. i. like masonry and concrete.M. If the Column ductile link is the weak one (i. UK.e. Next. start the tractor and pull the 0. Now. In general. (19 70). For the same amount of pull for ce. buildings are usually in the range 0. cut the Low-rise rope! The building will oscillate back-and-forth Building: horizontally and after some time come back to the 0. Chapter 16. Earthquake Eng ine erin g. Prentice Hall. Inverted Pendulum Model Figure 2: Fundamental natural periods of structures differ ov er a large range. Any alterations made to the moves with the ground. Value of T depends on the 2 sec building flexibility and mass. taller buildings are more flexible and have larger mass.00 sec.4 s ec original position (Figure 1b).to medium-rise buildings generally have shorter T (less than 0. Elevated Water Tank: 4 sec Large Concrete Gr avity Dam: 0. one complete back-and-forth Reinforced motion) is the same and is called Fundamental Natural Concrete Chimney: Period T of the building. then every point periods T of n ormal single storey to 20 storey in it would move by the same am ount as the ground. more the flexibility.. Learning 10 Earthquake Design Earthquake Tip and Construction How Flexibility of Buildings Affects their Earthquake Response? Oscillations of Flexible Buildings Fundamental natural period T is an inherent When the ground shakes. Fundamental natural and-forth. If the building were rigid.8 s ec (a) Building pulled with a rope tied at its roof Roof T T Displacement T T Time 0 Suspension Bridge: 6 s ec Adapted from: Newm ark. these oscillation s are 15 Stor ey Building: periodic. 19 . The time taken (in seconds) for each complete 1 sec cycle of oscillation (i. USA. the longer is the T. the longer is the T. shown in Figure 2.05-2.4 sec). Some But. and more the mass. The (b) Oscillation of building on cutting the rope natural period values are only indicative. Curre nt trends in the Seism ic Analysis a nd Des ign of Hi gh Ris e Structures. and different parts examples of natural periods of different structures are move back-and-forth by different amounts. On the contrary. natural period may vary considerably. building will change its T. Take a fat coir rope and tie one end of it to the roof Single Storey of a building and its other end to a m otorized vehicle Building: (say a tractor). and therefore have a longer T. the base of a building property of a building. low. and the building swings back.05 sec building. (1970).e. the movement is larger for a more flexible building. the back-and-forth motion is periodic. it will move in the direction of pull (Figure 1a). Figure 1: Free vibration response of a building: depending on actual properties of the structure. in Wiegel. most buildings are flexible. some earthquake (a) Buildings in a city lie on different soils Adapted from: Seed and Idriss.org or a filter. some buildings will be shaken more than the others. USA. the periods and amplitude of the Engineering Research Institute. some items in buildings. Short 20 Period 0 Time Wave Tshort 10 0 0 50 100 150 200 250 300 Time Depth of Soil (m) 0 (b) Intensity of damage depends on thickness of underlying soil layer: 1967 Caracas Earthquake Amplitude Figure 4: Different Buildings Respond Differently Long to Same Ground Vibration.R. Authored by: C. if the earthquake ground motion has long IITK-BMTPC Earthquake Tip 5: What are the Seismic Effects on period waves. The time taken by the wave to complete one cycle of m otion is called period of the earthquake wave. Even within this range. Dynamics of Structures – A Primer. On the other Sponsored by: Building Materials and Technology Promotion hand. but was minimal in areas with larger thickness of soil cover. This release is a property of IIT Kanpur and BMTPC New 300m. allowing some ground waves to pass through www. The stories of multi-storey buildings. the response of buildings was found to depend on the thickness of soil under the buildings.. These damages may ground motion under these buildings varies across the not affe ct safety of buildings.in. For example.. 0.bmtpc. earthquake waves). Prentice Hall Inc. the damage intensity Council.ac.. cannot take large lateral movements. Next Upcoming Tip What are the Indian Seismic Codes? During the 1967 Caracas earthquake in South America. the damage intensity was just the reverse in the case of 10-14 storey buildings.nicee.e. (1982). Earthquake Engineering. and small for lower thickness of soil cover. USA. injuries and panic among its residents. If the ground is shaken back-and-forth losses.IITK-BMTPC Earthquake Tip 10 How Flexibility of Buildings Affects their Earthquake Response? page 2 Importance of Flexibility The ground shaking during an earthquake contains a mixture of many sinusoidal waves of different frequencies. New Delhi. India soil cover of around 40-60m thick.K. Earthquake ground motion (i.V. Ground waves are stronger than the others. India was more when the soil cover was in the range 150. I t may be reproduced without ch anging its conten ts and with du e acknowled gemen t. contents. One way of categorizing Unsecured shelves might topple. but may cause economic city (Figure 4a).org. the epicentral distance. Thus.Murty Figure 4b shows that for buildings 3-5 storeys tall..03-33sec. Visit www.A. Intensity of earthquake waves at a particular building location Structural Dam age Intensity (%) 50 depends on a number of factors. and 40 10-14 Storey the type of ground that the earthquake waves travelled Buildings through before reaching the location of interest. like glass windows. In a typical city. Suggestion s/co mmen ts Here. 30 3-5 Storey Buildings EERI. and filtering the rest. especially at upper them is by their fundamental natural period T. different sizes and shapes. including the magnitude of the earthquake. there are buildings of many and are therefore damaged severely or crushed. (1980). earthquake shaking of the ground has waves whose periods vary in the range Earthquake Shaking Motion an d Soil L iqu efaction D urin g Earthqu akes. by earthquake waves that have short periods. (1970). IITK-BMTPC Eart hquake Tip 2: How t he Ground Shakes? Similarly. In general. then long period buildings will have Structures? larger response. depending on the value of T of Resource Material the buildings and on the characteristics of earthquake Wiegel. to see previous IITK-BMTPC Earthquake Tips. the damage intensity was higher in areas with underlying Indian Institute of Technology Kanpur Kanpur. Period 0 Time Wave Tlong Flexible buildings undergo larger relative horizontal displacements. Delhi. the soil layer under the building plays the role of may be sent to: eqtip s@iitk. ranging from short to long periods (Figure 3). January 2003 20 . which may result in damage Figure 3: Strong Earthquake Ground Motion is to various n onstructural building components and the transmitted by w aves of different periods.R. USA. Chopra. then Related Tip short period buildings will have large response. to the extent possible. its stiffness. 1993. the Bureau of Indian Standards (BIS) has the following seismic codes: IS 1893 (Part I). shape and of the structure. 2002. Indian Standard Guidelines for Improving Zone Earthquake Resistance of Low Strength Masonry V Buildings Figure 1: Seismic Zone Map of India show ing IS 13920. detailing and IS 1893 is the main code that provides the seismi c constructing of structures. and its ductility. 1993. and materials and methods used in constructi on. they are indicative of the level of progress a country has made in the field of earthquake engineering. the seismic coefficient for a single-storey (c) Adequate Stiffness: Its lateral load resisting system is building may have 2. Indian Standard Criteria for Earthquake Resistant Design of Structures (5th Revision) IS 4326. building typologies. 1993. the soil on the ground.5 times that of a 15-storey such that the earthquake-induced deformati ons in building. Indian Standard Guidelines for Improving Earthquake Resistance of Earthen Buildings Seismic IS 13828. designing. Structures need The regulations in these standards do not ensure to be designed to withstand such forces and that structures suffer no damage during earthquake of deformations. they ensure behaviour of structures so that they may withstand the that structures are able to respond to earthquake earthquake effects without significant l oss of life and shakings of moderate intensities without structural property. The first formal seismic code in India. But.over 60% of India’s land Ductile Detailing of Reinforced Concrete Structures under seismic zones III. 1993. Indian Standard Code of Practice for four seismic zones . ensure a direct and smooth flow of inertia forces to importance of the structure. Today. namely IS 1893. 1993. Similarly. (d) Good Ductility: Its capacity to undergo large deformations under severe earthquake shaking even after yielding. Indian Seismic Codes Seismic codes are unique to a par ticular region or country. IV and V. the latter in turn depends on structural system carrying loads are such that they properties like seismic zone in which structure lies. induced in it does not result in collapse. They take into account the local seismology.25 times the seismic force that it can resist is such that the damage design force of an identical building in Bombay. Further. Seismic codes help to improve the all magnitudes. is improved by favourable design and detailing strategies. a (b) Lateral Strength: The maximum lateral (horizontal) building in Bhuj will have 2. procedures outlined in seismic codes to help design IS 1893 engineers in the planning. namely: This force depends on the mass and seismic coefficient (a) Good Structural Configuration: Its size. Seismic codes cover all these aspects. which it rests. For example. building has four virtues in it. Learning 11 Earthquake Design Earthquake Tip and Construction What are the Indian Seismic Codes? Importance of Seismic Design Codes IS 13935. Indian Standard Guidelines for Repair and Ground vibrations during earthquakes cause Seismic Strengthening of Buildings forces and deformati ons in structures. was published in 1962. An earthquake-resistant zone map (Figure 1) and specifies seismic design force. it do not damage its contents under low-to- moderate shaking. Countries around the world have damage and of heavy intensities without total collapse. accepted level of seismic risk. Indian Standard Code of Practice for Earthquake Resistant Design and Construction of Buildings (2nd Revision) IS 13827. Subjected to Seismic Forces 21 . architectural components of buildings. Building Materials and Technology Pr omotion Council. Bridges and Retaining masonry and wooden buildings. codes are conceptually the same. like clay-mud. Some In contrast. and those in IS 13828 with Structure and Sub-Struct ure of Bridges and for Asse ssment of the Strength of Existing Bridges.Murty designed and detailed as per the Indian Code IS 456 Indian Institute of Technology Kanpur (2002). and Bridge developed earthquake codes. Today. India in IS 13920 (1993). I t may be reproduced without ch anging its conten ts and with du e acknowled gemen t. After the a variety of structures. IV and V. Government of India. IS 13920. yet available in the Indian codes. Explanatory Handbook on Codes for Earthquakes them are termed non-engineered. IV and V. (2000). All Japan. Constructions based on SP 22 (S&T). and 1893 will cover: Liquid-Retaining Tanks. However. New includes burnt clay brick or stone masonry in weak Delhi.bmtpc. frame or shear wall buildings as a whole. in 2002. India regions require ductile design and detailing. features for improving earthquake resistance of IRC 6. Thus. but does not cover reinforced concrete (Part 5). Inclusion of features Next Upcoming Tip mentioned in these guidelines may only enhance the How do masonry bu ildings behave during earthquakes? seismic resistance and reduce chances of collapse. Ministry of general principles of design and special construction Railways (Railway B oard).org or design and ductile detailing of steel structures are not www. both elevated techniques for repair/seismic strengthening of and ground supported (Par t 2). The code provides a Walls (Part 3). Suggestion s/co mmen ts zones III.IITK-BMTPC Earthquake Tip 11 What are the Indian Seismic Codes? page 2 The revised 2002 edition. This code covers general principles for earthquake resistant buildings. Selection of materials and special Related Tip features of design and constructi on are dealt with for Tip 4: Where are the seismic zones in India? Tip 8: What is the seismic design philosophy of buildings? the following types of buildings: timber constructions.Section II: Loads and Stresses. Bridge Rule s. The other four parts of IS seismic strengthening. Provisions for Bridges Seismic design of bridges in India is covered in In Closure… three codes. and Dams and Embankments in such buildings. IS 456. Rules Sp ecifying the Loads for the Desig n of Super- resistance of earthen houses. Similar provisions for seismic may be sent to: eqtip s@iitk. New Delhi. structures located in high seismic Kanpur.R. (2000).org. this This release is a property of IIT Kanpur and BMTPC New code has been made mandatory for all structures in Delhi. 1993 Authored by: In India. (1982). 1993 and IS 13828. the key to ensuring earthquake safety lies in improvements to the IRC6 (2000) seismic provisions. interim provisions that make significant However. and are not totally Engineer ing . After the 2001 Bhuj earthquake. the IRC released strength masonry houses to modern buildings. New Delhi. countries like Rules (1964) from the Ministry of Railways. namely IS 1893 (1984) from the BIS. the 1984 edition of IS1893 had provisions guidelines are also laid down for non-structural and for all the above structures in a single document.V. These standards are applicable Concrete. have detailed seismic code provisions. Guidelines: Improving Earthquake Resistance of Housing . even though there India has a fairly good range of seismic codes covering are some differences in their implementation. 1993 BMTPC. Indian Standard Code of Practice for Plain and Reinforced mortars.IS 1893:1975 and IS 4326:1976. Industrial Structures including Stack. Indian Roads Con gress. selection of materials. Part 1 of IS1893.ac. Standard Specifications and Code of Practice for Road buildings of low-strength masonry. New Delhi. in seismic zones III. Development of and all railway bridges with Bridge Rules. and constructi on aspects for improving earthquake. Bureau of Indian free from collapse under seismic shaking intensities Standards. This masonry Bridges . (2000).in. contains IS 13935. Visit www. Resource Material IS 13827. ranging from mud or low- 2001 Bhuj earthquake. 1993 provisions that are general in nature and those These guidelines cover general principles of applicable for buildings. highway bridges are required to comply with IRC 6. New Zealand and the United States of America. New Guidelines in IS 13827 deal with empirical design Delhi. Bureau of Indian Standards. These four documents are under preparation. VIII (MMI) and higher.nicee. These three building codes in India started rather early. having a robust mechanism that enforces and implements these design code provisions in actual IS 4326. Tip 9: How to make buildings ductile for good seismic performance? masonry constructions using rectangular masonry Tip 10: How flexibility of buildings affects their earthquake units. February 2003 22 . 1993 constructions. IRC 6 Countries with a history of earthquakes have well (2000) fr om the Indian Roads Congress. to see previous IITK-BMTPC Earthquake Tips. reinforced con crete structures are C. and buildings with prefabricated reinforced response? concrete roofing/flooring elements. Provisions Sponsored by: for the ductile detailing of monolithic reinfor ced Building Materials and Technology Promotion concrete frame and shear wall structures are spe cified Council. brief coverage for individual reinforced concrete members Like Structures (Part 4). (1964). A number of earthquake-resistant (IITK-BMTPC Earthquake Tip 5). The main emphasis is on ensuring that tied together like a box. all walls masonry building (roof. If all the walls are not foundation. the walls loaded in their weak these forces reach the ground with out causing major direction tend to topple (Figure 2a). the walls are most vulnerable to damage caused way. 23 . Horizontal inertia force developed inertia forces at locations of mass in the building. only possible if walls are well connected. the features can be introduced to achieve this objective. In this 1a). at the roof transfers to the walls acting either in the These forces travel through the roof and walls to the weak or in the strong direction. A wall topples Masonry buildings are brittle structures and one of down easily if pushed horizontally at the top in a the most vulnerable of the entire building stock under direction perpendicular to i ts plane (termed weak strong earthquake shaking. walls loaded in their weak direction can take advantage of the good lateral resistan ce offered by walls loaded in their strong directi on (Figure 2b). However. The large number of direction). it i s very The ground shakes simultaneously in the vertical important to improve the seismic behaviour of and two h orizontal directions during earthquakes masonry buildings. Thus. Roof Toppling A B Foundation B (a) Basic components of a masonry building Pushed i n the plane of the wall A Direction of earthquake shaking Weak A (a) For the direction of earthquake shaking shown. damage or collapse. walls also need to be tied to the roof and Walls foundation to preserve their overall integrity. Of the three components of a To ensure good seismic performance. Further. Direction wall B tends to fail Toothed joints in masonry courses A Direction of B B or L-shaped dowel bars earthquake s haking Strong Toppling B Direction A Pushed perpendicular to the plane of the w all Direction of earthquake Direction of shaking earthquake shaking (b) Direction of force on a wall critically determines (b) Wall B properly connected to Wall A (Note: roof its earthquake performance is not shown): Walls A (loaded in strong direction) Figure 1: Basic components of a masonry support Walls B (loaded in weak direction) building – walls are sensitive to direction of Figure 2: Advantage sharing between walls – earthquake forces. Learning 12 Earthquake Design Earthquake Tip and Construction How do brick masonry houses behave during earthquakes? Behaviour of Brick M asonry Walls by horizontal forces due to earthquake. earthquakes in India corroborates this. horizontal vibrations are the most damaging to normal Ground vibrations during earthquakes cause masonry buildings. but offers much greater resistance if pushed human fatalities in such constructions during the past along its length (termed strong direction) (Figure 1b). wall and foundation) (Figure must be joined properly to the adjacent walls. mud mortar is the in comparison to its thickness.. stone blocks. Of these. Paulay. A 10mm thick mortar layer is generally satisfactory from practical and aesthetic considerations. to see previous IITK-BMTPC Earthquake Tips. Cement-sand mortar with lime is the most suitable. Indian Standard Code of Practice for Structural Use of Unreinforced Masonry. flows outward vulnerable to shaking in its weak direction (Figure 3). Bricks must be str onger than mortar. e. March 2003 24 ..org. cement-sand. Large portion of wall from roof IS 13828. the effect of roof on walls is not shown. The properties of these earthquake shaking is by making them act together as materials vary across India due to variation in raw a box along with the r oof at the top and with the materials and construction methods. A number of construction masonry units are used in the country. Secondly. Visit www. Inertia force New Delhi.T. New Delhi. IS 4326. (1992). New Delhi.nicee. Indian Standards prescribe the preferred types and grades of bricks and mortars to be used in buildings in each seismic zone. A wall that is too tall or too long or cement-sand-lime. the amount of water drawn away from the mortar. Indian Standard Code of Practice for Earthquake Resistant Design and Construction of Build ings. (1993). New Delhi. For this offered by the wall. New York. Bureau of Indian Standards.IITK-BMTPC Earthquake Tip 12 How do brick masonry houses behave during earthquakes? page 2 How to Improve Behaviour of M asonry Walls Choice and Quality of Building M aterials Masonry walls are slender because of their small Earthquake performance of a masonry wall is very thickness compared to their height and length. clay bricks aspects are required to ensure this box action. A sensitive to the properties of its constituents. is particularly weakest. smaller the openings. (1987). www. it crushes easily when dry. the larger is the resistance and in difficulty in positioning masonry units.V.N. concrete blocks (solid and connections between the walls should be good. namely simple way of making these walls behave well during masonry units and mortar. stretches without crumbling at low earthquake shaking. Indian Standard Guidelines for Improving Earthquake not supported by cross walls Resistance of Low-strength Masonry Buildings. Firstly. bricks with low porosi ty are to be used.. The earthquake response of masonry walls depends on the relative Overturning strengths of brick and mortar.g. Note: In this may be sent to: eqtip s@iitk. (1993). Burnt clay bricks are most can be achieved by (a) ensuring good interlocking of commonly used. mud. the sizes of bricks suck away water from the adjoining mortar. limits for these ratios. Excessive thickness of mortar is not Overturning desirable.ac.. and topple when pushed in the weak direction can be they must be soaked in water before use to minimise reduced by limiting its length-to-thickness and height. the masonry courses at the juncti ons. and has very low earthquake resistance. This mortar mix provides excellent workability for laying bricks. This hollow). detrimental to good masonry behaviour because the particularly at the lintel level. and Priestley.J. to-thickness rati os (Figure 3). I t may be reproduced without ch anging its conten ts and with du e acknowled gemen t.org or figure. Suggestion s/co mmen ts and length to be kept within limits.g.M. India Sponsored by: Short Wall Building Materials and Technology Promotion Good support offered by cross walls Council. India This release is a property of IIT Kanpur and BMTPC New Figure 3: Slender w alls are v ulnerable – height Delhi. the tendency of a wall to reason. John Wiley & Sons. Seism ic Design of Re inforced Cross W all Concrete and Masonry Buildings. The which results in poor bond between brick and mortar. Cross W all Long Wall Next Upcoming Tip Why should masonr y houses have simple structural configuration? Authored by: C.Murty Indian Institute of Technology Kanpur Kanpur. Excessive porosity is employing horizontal bands at various levels.bmtpc. e. and bonds well with bricks. These bricks are inherently porous.in. Thirdly. Design codes specify Various mor tars are used. Bureau of Indian Standards. door and window openings need to be kept small. and (b) and so they absorb water. Soil Soil Related Earthquake Tip Thick Wall ( 1½ brick) Short Wall ( 1 brick) Tip 5: What are the seismic effects on structures? versus versus Resource Material Thin Wall ( 1 brick) Tall Wall ( 1 brick) IS 1905. A variety of foundation at the bottom.R. Bureau of Indian Standards. (burnt and unburnt). Hence. To understand this. tall. Openings too close to wall unduly slender walls are threats to good seismic corners hamper the flow of forces fr om one wall to behaviour. i. Large. To be more specifi c.e. Tip 6). Figure 2: Regions of force transfer from weak walls to strong w alls in a masonry building – However. A strategy used in making them earthquake. masonry buildings in earthquakes. Walls shaken in the weak direction shaking. direction shown in Figure 2. Further.. it is best to keep all openings as small as possible and as far away from the corners as possible. elements of the building. 25 . walls B1 and B2 building construction is to ensure that these effe cts are seek support from walls A1 and A2 for shaking in the sustained without major damage or collapse. the masonry courses from the walls meeting at resistant is developing good box action between all the corners must have good interlocking. while wall B2 pushes help achieve this. Then. They develop numerous cracks under both the weak direction of others (See IITK-BMTPC compressive and tensile for ces caused by earthquake Earthquake Tip 12). large openings weaken at the lintel level ties the walls together and helps to walls fr om carrying the inertia forces in their own make them behave as a single unit. plane. Learning 13 Earthquake Design Earthquake Tip and Construction Why should masonry buildings have simple structural configuration? Box Action in M asonry Buildings consider a four-wall system of a single storey masonry Brick masonry buildings have large mass and building (Figure 2). the direction of The structural configuration of masonry buildings shaking could change to the horiz ontal direction includes aspects like (a) overall shape and size of the perpendicular to that shown in Figure 2. Loosely connected roof or seismic performance. while wall B2 assume significance in deciding the performance of pushes walls A1 and A2.. against them. For example. inertia hence attract large horizontal forces during earthquake forces act in the str ong direction of some walls and in shaking. strong ones and A1 and A2 weak. i. During earthquake shaking. location and size of openings in walls wall B1 pulls walls A1 and A2. At the next instance. The focus of ear thquake resistant masonry seek support from the other walls. Thus. and (b) distribution of mass and (horizontal ) and B change their roles. long and unsymmetric buildings perform Thus. between roof. Roof that stays together as a single Good integral unit during earthquakes Inertia force connection from roof between roof and walls Inertia force Walls with small from roof openings A1 Lintel B2 Band B1 A2 Good Stiff Foundation connection between walls and Good connection foundation Regions at wall corners where load Direction of transfer Figure 1: Essential requirements to ensure box earthquake takes place action in a masonry building. walls A building.e. a horizontal band introduced another (Figure 3). walls transfer loads to each other at their poorly during earthquakes (IITK-BMTPC Earthquake junctions (and through the lintel bands and roof). For this reason. wall Appropriate choice of structural configuration can B1 pulls walls A1 and A2. walls and openings near the wall corners are detrimental to good foundation (Figure 1). Walls B1 and B2 become the lateral load resisting elements across the building. shaking from one wall to another Influence of Openings Openings are functional necessities in buildings. Next Upcoming Tip staircases are completely separated (Figure 4b) and Why are horizontal bands necessary in masonry buildings? built on a separate reinforced concrete structure. E and Y. staircase in masonry building Inclined staircase slabs in masonry buildings offer – must be carefully designed and constructed. New Delhi. another concern. adequate gap is necessary between these different blocks of the building.ac.org or Tomazevic. Indian Standard Code of Practice for Earthquake Building Materials and Technology Promotion Resistant Design and Construction of Build ings.g.. T. (1993). India IS 1905. During earthquakes.in. Indian Standard Code of Practice for Structural Use of Sponsored by: Unreinforced Masonry. Earthquake Resistant Design of Masonr y Buildings. if not accoun ted for in stair case Tip12: How brick masonry houses behave during earthquakes? design and construction. it may not be (b) Building with separated staircase necessary to provide such separati ons between blocks. sometimes. New Delhi. Reinforced Concrete Earthquake-Resistant Features Stair Case Tower Indian Standards suggest a number of earthquake. say up Figure 4: Earthquake-resistant detailing of to ~15-20% of the length of building in that direction.Murty pound each other during strong earthquake shaking. and with du e acknowled gemen t. (1987). Suggestion s/co mmen ts may be sent to: eqtip
[email protected]. New Delhi.IITK-BMTPC Earthquake Tip 13 Why should masonry buildings have simple structural configuration? page 2 Large window opening Tall reduces the slender wall strength wall in its strong direction Inertia force of roof mass Damage Damage Diagonal bracing Door opening close to wall cor ner effec t weakens the c onnection between walls Damage Figure 3: Openings weaken walls in a masonry building –a single closed horizontal band must (a) Damage in building with rigidly built-in staircase be provided above all of them. be separated into (almost) simple rectangular blocks in plan. separated blocks can oscillate independently and even hammer each other if they are too close.org. Indian Standard Guidelines for Improving Earthquake This release is a property of IIT Kanpur and BMTPC New Delhi. To overcome this. Thus.R. if horizontal pr ojecti ons in buildings are small. to see previous IITK-BMTPC Earthquake Tips. IS 42326. (or Mumty) resistant measures to develop good box-type action in masonry buildings and improve their seismic performance. Visit www. Bureau of Indian Standards. The Indian Standards suggest minimum seismic separations between blocks of buildings. IS 13828. London.V. India Standards. However. Bureau of Indian Council. each of which has simple and good earthquake behaviour (IITK-BMTPC Earthquake Tip 6). Adequate gap is provided between the staircase tower Authored by: and the masonry building to ensure that they do not C. (1993). Imperial College Press. I t may be reproduced without ch anging its conten ts Resistance of Low-strength Masonry Buildings.. April 2003 26 . like a building with plan shapes L. These are areas of potential damage in Tip 6: How architectural features affect building s during earthquakes? masonry buildings. (1999). it is suggested that a Gap building having horizontal projecti ons when seen from the top.bmtpc. www. Indian Institute of Technology Kanpur Resource Material Kanpur. For instance.M. An integrally connected staircase slab acts like a cross-brace between fl oors and transfers Related Earthquake Tip large horizontal forces at the r oof and lower levels Tip 5: What are the seismic effe cts on structures? (Figure 4a). Bureau of Indian Standards. UK. New Delhi. e. The lintel band is the most thereby improves their stability in the weak direction. lintel walls loaded in str ong direction. the earthquake-resistant feature in masonry buildings. In buildings scale. important of all. Most masonry houses sustained partial or with flat reinforced concrete or reinforced brick roofs. Plinth bands are bands are provided to hold a masonry building as a primarily used when there is concern about uneven single unit by tying all the walls together. This band also band and plinth band (Figure 1). roof band needs to be Horizontal bands are the most importan t provided. However. On the other hand. There are four types of bands in a typical a support for walls loaded along weak directi on fr om masonry building.one masonry house in Killari village had Figure 1: Horizontal Bands in masonry building – horizontal lintel band and sustained the shaking Improve earthquake-resistance. without damage. because the roof slab also was one masonry building in the village. the buildings. Roof Masonry abov e lintel Lintel Band Masonry below lintel Wall Plinth Band Foundation Soil (a) Building with Flat Roof (a) Building with no horizontal lintel band: Gable-roof collapse of roof and walls connection Gable Roof Band Truss-wall Band connection Floor-walls Lintel connection Band Lintel Band Cross wall (b) A building with horizontal lintel band in Killari Plinth connection Band village: no damage Peripheral wall connection Figure 2: The 1993 Latur Earthquake (Central (b) Two-storey Building with Pitched Roof India) . The roof band is very important. the complete collapse (Figure 2a). there roof band is not required. The gable band is employed only in intensity of shaking in Killari village was IX on MSK buildings with pitched or sloped roofs. and are settlement of foundation soil. which had a plays the role of a band. roof band. named after their reduces the unsupported height of the walls and location in the building. in buildings with lintel band and it sustained the shaking very well with hardly any damage (Figure 2b). and needs to be provided in almost all During the 1993 Latur earthquake (Central India). namely gable band. 27 . similar to a cl osed belt provided around cardboard The lintel band ties the walls together and create s boxes. Learning 14 Earthquake Design Earthquake Tip and Construction Why are horizontal bands necessary in masonry buildings? Role of Horizontal Bands flat timber or CGI sheet roof. In buildings with pitched or sloped roof. available on www. in A RC bands. Small lengths of wood spacers (in wooden bands) or steel links (in RC bands) are used to make the straight lengths of wood runners or steel Steel bars act together. Bureau of Indian Standards.IITK-BMTPC Earthquake Tip 14 Why are horizontal bands necessary in masonry buildings? page 2 Design of Lintel Bands Wood Spac ers During earthquake shaking. This will allow the band to support walls loaded in their weak direction by walls loaded in their (a) Wooden Band strong direction. to see previous IITK-BMTPC Earthquake Tips. Direction of Related Earthquake Tip earthquake Tip 5: What are the seismic effects on structures? shaking Tip12: How brick masonr y houses behave during earthquakes? Tip13: Why masonry buildings should have simple structural configuration? Resource Material 150 IAEE. International Association for Earthquake Engineering. Tokyo. (1986). the lintel band undergoes bending and pulling actions (Figure 3). the minimum Delhi. I t may be reproduced without ch anging its conten ts thickness is 75mm. Authored by: C.in. www. the RC bands are the best.R. New Delhi. India The Indian Standards IS:4326-1993 and IS:13828 Sponsored by: (1993) provide sizes and details of the bands.Murty Indian Institute of Technology Kanpur Indian Standards Kanpur. New Delhi. (1993).org. Suggestion s/co mmen ts diameter are required.nicee. When Building Materials and Technology Promotion wooden bands are used. The straight B lengths of the band must be properly connected at the wall corners. Small Large IS 13828. India to be at least 75mm 38mm and of spacers at least This release is a property of IIT Kanpur and BMTPC New 50mm 30mm. New Delhi.nicee. tied across with steel links of at may be sent to: eqtip s@iitk. the construction of lintel band Wood requires special attention.ac. the cross-se ction of runners is Council. adequate anchoring of steel links with steel Steel Bars bars is necessary. B Correct Bending of Pulling of Practices Lintel Band Lintel Band Lintel Band Direction of Inertia Force Incorrect Practice (b) RC Band Figure 4: Horizontal Bands in masonry buildings – RC bands are the best.bmtpc. In wooden bands. and at least two bars of 8mm and with du e acknowled gemen t. Bands can be made of wood Runners (including bamboo splits) or of reinforced concrete A (RC) (Figure 4). Indian Standard Code of Practice for Earthquake Resistant Design and Construction of Build ings. Indian Standard Guidelines for Improving Earthquake Resistance of Low-strength Masonry Buildings. May 2003 28 . proper nailing of Links straight lengths with spacers is important. Guidelines for Earthquake Resistant Non-Engineered 75 mm mm Construction. Lintel Bands Next Upcoming Tip Why is vertical reinforcement required in masonry build ings? Figure 3: Bending and pulling in lintel bands – Bands must be capable of resisting these. (1993).org or least 6mm diameter at a spacing of 150 mm centers.org. Bureau of Indian Cross-section of Standards.V. Likewise. When RC bands are used. IS 4326. To resist these actions. Visit www. lintel band and roof Roof Band band. a roof band is also provided. wall pier masonry and sill masonry. Foundation Plinth Roof SoilMasonry Band (a) Building Components Pier Spandrel Masonry Lintel Level Wall Pier Rocking Masonry of Pier Sill Level Sill Crushing Masonry Plinth Level Foundation Soil Uplifting of masonry (b) Rocking of Masonry Piers Figure 1: Sub-units in masonry building – walls behave as discrete units during earthquakes. Otherwise. Since the roof is a hipped one. masonry Lintel buildings are weakened by the openings in their walls Band Door Window (Figure 1). force Sliding In un-reinforced masonry buildings (Figure 3). weight of the structure above is small. During strong earthquake shaking. It Piers has lintel and plinth bands. Learning 15 Earthquake Design Earthquake Tip and Construction Why is vertical reinforcement required in masonry buildings? Response of M asonry Walls Horizontal bands are provided in masonry Roof buildings to improve their earthquake performance. X-Cracking Consider a hipped roof building with two window of Masonry openings and one door opening in a wall (Figure 2a). developing contact only at the opposite diagonals (Figure 2b). and type of doorframes used. the building may slide just under the roof. Sometimes. The exact l ocati on of Foundation sliding depends on numerous fa ctors including building weight. Rocking is possible when masonry piers are slender. the piers are more likely to develop diagonal (X-type) Roof Earthquak e- shear cracking (Figure 2c). the earthquake-induced inertia force. below the lintel band or at the sill level. The rocking of a masonry pier Figure 2: Earthquake response of a hipped roof masonry building – no vertical reinforcement can crush the masonry at the corners. masonry building – no vertical reinforcement. These masonry sub-units rock back (c) X-Cracking of Masonry Piers and forth. namely spandrel masonry. During earthquake shaking. When the ground shakes. the inertia force causes the small-sized Foundation masonry wall piers to disconnect from the masonry Soil above and below. the masonry Opening Opening walls get grouped into three sub-units. 29 . Even if horizontal bands are provided. These bands include plinth band. and when is provided in walls. this is the most common induc ed inertia failure type in masonry buildings. Figure 3: Horizontal sliding at sill level in a the area of openings. the cross-secti on area of the masonry wall reduces at the opening. the building may also slide at the plinth level. (a) Cracking in building with no corner reinforcement Bending Lintel Band Reinforcement of Pier Bars Sill Band (Similar to Lintel Ba nd. – wall behaviour is modified. John Wile y (b) Vertical reinforcement prevents sliding in walls & Sons..in.two opposite Indian Institute of Technology Kanpur corners move away and the other two come closer. New Delhi. Figure 4: Vertical reinforcement in masonry w alls New Delhi. but disconti nue d at door ope nin gs) Vertical steel bars anchored i n foundation and roof band (b) No cracks in building with vertical reinforcement (a) Vertical reinforcement causes bending of masonry piers in place of rocking (See Figure 2). June 2003 30 . (1993). Indian Standard Guidelines for Improving Earthquake Sliding failure mentioned above is rare. is Next Upcoming Tip diagonal X-cracking of wall piers. to see previous IITK-BMTPC Earthquake Tips. the vertical bars enhance their capability to resist horizontal earthquake forces and delay the X-cracking. IS 4326. Further. forces the slender masonry piers to undergo bending instead of rocking. Simplified Des ign of Masonry Structur es.nicee. Adequate cross-secti onal area of these vertical bars prevents the bar from yielding in tension. Suggestion s/co mmen ts vertical reinforcement adja cent to vertical edges. Visit www. even in Resistance of Low-strength Masonry Buildings. When a wall with an opening deforms during Authored by: earthquake shaking. the shape of the opening distorts C.V. Bureau of Indian Standards.. India Under this type of deformation. Delhi. Figure 5: Cracks at corners of openings in a masonry building – reinforcement around them helps. Bureau of Indian unconfined masonry buildings. Kanpur. BMTPC. may be sent to: eqtip s@iitk. In wider wall piers. (1991).R.bmtpc. common damage. the corners that come Sponsored by: closer develop cracks (Figure 5a). Protection of Openings in Walls IS 13828. New Delhi. The cracks are bigger Building Materials and Technology Promotion when the opening sizes are larger. Build ing Materials and Technology Promotion Council. (1993). Housing. Steel bars provided Council. provide protection against this type of damage. Indian Standard Code of Practice for Earthquake Resistant Design and Construction of Build ings. observed after an earthquake. and and with du e acknowled gemen t. Guidelines: Improving Earthquake Resistance of (See Figure 3). However. Related . the most Standards.org. I t may be reproduced without ch anging its conten ts lintel and sill bands above and below openings. India in the wall masonry all around the openings restrict This release is a property of IIT Kanpur and BMTPC New these cracks at the corners (Figure 5b).Murty and becomes more like a rhombus . IITK-BMTPC Earthquake Tip 15 Why is vertical reinforcement required in masonry buildings? page 2 How Vertical Reinforcement Helps Earthquak e-induced inertia force Embedding vertical reinforcement bars in the edges of the wall piers and anchoring them in the foundation at the bottom and in the roof band at the Cracking top (Figure 4). Earthquake Tip Tip 5: What are the seismic effects on structures? Tip12: How brick masonr y houses behave during earthquakes? Tip13: Why masonry buildings should have simple structural configuration? Tip14: Why horizontal bands are required in masonry buildings? Resource Material Amrose. New York.org or www. and also inclined How to improve seismic behaviour of stone masonr y buildings? cracks at the corners of door and window openings. USA.J.ac. Inc. the vertical bars also help protect the wall fr om sliding as well as from collapsing in the weak direction. In summary. (2000). New Delhi. There are huge numbers of stone buildings The main patterns of earthquake damage include: in the coun try. (c) separation of poorly constructed roof fr om riverbeds bound with mud mortar. Likewise. but qualitatively Yugoslavia). direction into two distinct wythes (Figure 2a). But. However. Learning 16 Earthquake Design Earthquake Tip and Construction How to make Stone Masonry Buildings Earthquake Resistant? Behaviour during Past India Earthquakes masonry dwellings. and should be avoided in high robust appearance of stone construction. ranging from rural houses to royal (a) bulging/separation of walls in the horizontal palaces and temples. disintegration of walls and eventual collapse of the and hence do not have the usual layers (or courses) whole dwelling. former these features is diffi cult to quantify. timber roof with thick mud overlay). A typical uncoursed random (UCR) stone masonry wall is illustrated in Figure 1. Turkey. The contribution of the each of other countries (e. a majority of the over Stone has been used in building construction in 13. Earthquake Resistant Features Laypersons may consider such stone masonry Low strength stone masonry buildings are weak buildings robust due to the large wall thickness and against earthquakes. These uncoursed walls have two exterior vertical layers (called wythes) of large stones. The design and construction features may raise the main deficiencies include excessive wall thickness. These features include: 31 . filled in between with loose stone rubble and mud mortar. (b) there are thick stone masonry walls (thickness ranges separation of walls at corners and T-junctions (Figure from 600 to 1200 mm) built using rounded stones from 2b). seen in brick walls. Greece. These walls are walls. and use of round stones (instead of shaped features these buildings may not become totally free ones). Vertically split Vertical gap layer of wall (a) Separation of a thick wall into two layers Vertically split layer of wall Mud mortar Outward bulging of vertical wall layer Half-dressed oblong stones (b) Separation of unconnected adjacent walls at junctions Figure 2: Maj or concerns in a traditional stone Figure 1: Schematic of the wall section of a house – deficiencies in walls. stones that go across split into 2 vertical layers. Such dwellings have shown very poor from heavy damage and even collapse in case of a performance during past earthquakes in India and major earthquake. earthquake resistance of these buildings and reduce absence of any connection between the two wythes of the loss of life. most of performance of stone masonry dwellings during past them buried under the rubble of traditional stone earthquakes. and (d) constructed with stones placed in a random manner. available. In many cases. these seismic zones. roof and in their traditional stone house – thick walls without connections have been prime causes for failure.800 deaths during 2001 Bhuj (Gujarat) earthquake is India since ancient times since it is durable and locally attributed to the collapse of this type of construction. in spite of the seismic the wall. The Indian Standard IS:13828-1993 buildings are one of the most defi cient building states that inclusion of special earthquake-resistant systems from earthquake-resistance point of view. In a typical rural stone house. Iran.000 people died.g. these walls support heavy roofs (for example. and eventual collapse of roof. over 8. In the 1993 Killari (Maharashtra) these features have been observed to improve the earthquake alone.. cement-sand mortar III and higher). and (b) Guidelines For Improving Earthquake Resistance of Housing (c) Manual for Repair and Reconstruction of Houses Damaged in chosen based on economy.Murty supports raised from the ground level called Indian Institute of Technology Kanpur buttresses should be provided at spacing not more Kanpur. for l onger walls. Indian Standard Guidelines . Earthquake Tip Tip14: Why horizontal bands are required in masonry buildings? Resource Material Brzev. Construction. Guidelines for Earthquake Resistant Non-Engineered preventing the wall from separating into wythes.M. practice is defi cient with regards to earthquake July 2003 32 . New Delhi. masonry dwellings must have horizontal bands Publications of B uilding Materials and Technology Promotion Council. and Sinha. It is important to Earthquake in October 1991 in the Garhwal Region of UP provide at least one band (either lintel band or roof Next Upcoming Tip band) in stone masonry construction (Figure 4). this type of stone masonry construction may be sent to: eqtip s@iitk. IS 13828. “Rubble stone masonr y 1200mm 1200mm <400mm walls with timber walls and timber roof.ac.S. I t may be reproduced without ch anging its conten ts least one-sixth its height. The height of each storey should not Sponsored by: exceed 3.org): roof and gable bands). stone masonry buildings Building Materials and Technology Promotion should not be taller than 2 storeys when built in Council.IITK-BMTPC Earthquake Tip 16 How to make Stone Masonry Buildings Earthquake Resistant? page 2 (a) Ensure proper wall construction The wall thickness resistance. (1986). New Delhi. (2001). to see previous IITK-BMTPC Earthquake Tips. ¾ths the w all thickness) stone Related . Instead.org. Thane. India than 4m. IAEE.V. 2001 (See www. Visit www. lintel. Greene. Through-stones (each extending Lintel Band over full thickness of wall) or a pair of overlapping bond-stones (each extending over at least ¾th s thickness of wall) must be used at every 600mm along the height and at a maximum spacing of 1.in. its extensive use is likely to continue due to should not exceed 450mm. The wall should have a thickness of at Delhi. cross C.R.net).org). the use of seismic bands is highly should be 1:6 (or richer) and lime-sand mortar 1:3 (or recommended (as described in feature (c) above and in richer) should be used.bmtpc. What are the seismic effects on RC frame buildings? (d) Control on overall dimensions and heights: The unsupported length of walls between cross-walls Authored by: should be limited to 5m. Also. (See IITK-BMTPC Earthquake Tip 14 for plinth. India cement mortar. In general. Bureau of Indian Standards. and holds the Pair of overlapping stones <1200mm walls together to resist horizontal earthquake (each of length at least Bond effects.org or www. But. Round stone boulders tradition and low cost. (1993). Use of mud mortar should be avoided in above (especially features (a) and (b) in seismic zones higher seismic zones.R. stones” in stone masonry w alls – vital in published by EERI and IAEE.world-housing. (b) Ensure proper bond in masonry courses: The masonry Discontinuiti es in lintel walls should be built in construction lifts not Horizontal band shoul d be av oided exceeding 600mm. and with du e acknowled gemen t. to protect human lives and should not be used in the constructi on! Instead.0m.. it is necessary to stones should be shaped using chisels and follow proper stone masonry constructi on as described hammers.nicee.bmtpc. New Delhi (www. the property in future earthquakes. The ACC Limited. Suggestion s/co mmen ts Although.niceee. and 1 storey when built in lime or This release is a property of IIT Kanpur and BMTPC New mud mortar.” World Housing Figure 3: Use of “through stones” or “bond Encyclopedia (www. India/Report 18.Improving Earthquake (c) Provide horizontal reinforcing elements: The stone Resistance of Low-Strength Masonry Buildings. IITK-BMTPC Earthquake Tip 14). W all Alternatives to Section Through Stones Wood plank < 600mm Hooked steel link S-shaped steel tie < 600mm <450mm Floor W all Level Plan Figure 4: Horizontal lintel band is essential in random rubble stone masonry w alls – provides integrity to the dwelling. These bands can be (a) Retrofitting of Stone Houses in Marathwada Area of Maharashtra constructed out of wood or reinforced con crete.2m along the length (Figure 3). However. Concrete is made of sand. 33 . columns and floor s are usually filled-in with masonry Earthquake shaking generates inertia forces in the walls to demarcate a floor area into functi onal spaces building. and then to the foundations from where they are movement. particularly in towns and known as the rigid diaphragm action (Figure 2b). when beams move with columns in the horizontal direction. and pr oper packing of gaps between RC frame and masonry infill walls. However. act like sacrificial fuses in buildings. Roles of Floor Slabs and M asonry Walls Floor slabs are horizontal plate-like elements. (b) In-plane Horizontal Movement A typical RC building is made of horizontal Figure 2: Floor bends w ith the beam but mov es members (beams and slabs) and vertical members all columns at that level together. also called Since most of the building mass is present at floor infill walls.thr ough slab and beams to columns and direction. Thus. When columns receive horizontal develop at the floor levels. And. and suppor ted by foundations that rest on ground. the columns (Figure 3). the Figure 3: Infill w alls mov e together w ith the slab usually forces the beams to move together with it. which can be life threatening. and steel bars can be bent into many shapes. these masonry walls. When beams bend in the vertical direction during earthquakes. namely concrete with reinforcing steel bars. Thus. these thin slabs Cracks bend along with them (Figure 2a). (columns and walls). they try to move in the horizontal downwards . are not connected to surr ounding RC levels. dispersed to the ground. but masonry walls tend to resist this walls. (rooms). beams and slabs at one storey level are cast together. two primary materials. structures of complex shapes are (a) Out-of-pl ane Vertical Mov ement possible with RC. columns under earthquake shaking. infill walls designed to be stronger than those in storeys above. 4 Earthquake performance of infill walls i s enhanced by mortars of good strength. placing Total Force infills irregularly in the building causes ill effects like Figure 1: Total horizontal earthquake force in a short-column effect and torsion (these will be discussed building increases dow nwards along its height. along its thin 1 direction). These for ces travel forces at floor levels. The system comprising of RC columns After columns and floors in a RC building are cast and connecting beams is called a RC Frame. vertical spaces between frame participates in resisting the earthquake forces. all mixed with pre-determined amount of water. which are proportional to the building mass. Due to their heavy weight and thickness. Also.. in subsequent IITK-BMTPC Earthquake Tips). crushed stone (called aggregates) and cement.e. Normally. which facilitate functi onal use of buildings. cities. since masonry is a brittle and walls at lower storeys experience higher material. Usually. these walls develop cracks once their ability earthquake-induced forces (Figure 1) and are therefore to carry horizontal load i s exceeded. As inertia forces accumulate these walls attract rather large horizontal for ces downwards from the top of the building. Gap In residential multi-storey buildings. making proper masonry Floor Level 3 courses. an infill wall 2 that is unduly tall or long in comparison to its thickness can fall out-of-plane (i. earthquake-induced inertia forces primarily columns and beams. the geometric distorti on of the slab In recent times. this behaviour is become common in India. thickness of slabs Compressi on is only about 110-150mm. they develop cracks under severe ground shaking but help share the 5 load of the beams and columns until cracking. Learning 17 Earthquake Design Earthquake Tip and Construction How do Earthquakes Affect Reinforced Concrete Buildings? Reinforced Concrete Buildings In most buildings. Concrete can be molded into any desired shape. reinforced concrete buildings have is negligible in the horizontal plane. The RC and the concrete hardens. Reinforced concrete (or simply RC) consists of Structural engineers must consider this during design. 2002) – for calculating earthquake forces. columns (which receive forces from beams) (a) Strong Columns.G.R. Suggestion s/co mmen ts and compression in members – reinforcement is may be sent to: eqtip
[email protected]. Under gravity loads.A. damage is tension in the beams is at the bottom surface of the likely to occur first in beams (Figure 5a). Further.E. This localized Figure 4d. Load Load Relevant Indian Standards The Bureau of Indian Standards. should be str onger than beams. When this strategy is adopted in design. steel bars are required on in all in one all faces of columns too. Ne w Delhi. Similarly. at the top and bending moment) generated in members are shown in bottom of a particular storey (Figure 5b).ac.V. 2003.G. the beam ends can Large Small displ aceme nt displ aceme nt develop tension on either of the top and bottom faces. storeys storey Strength Hierarchy For a building to remain safe during earthquake shaking. Penelis. Earthquake Tip Tip 5: What are the seismic effects on structures? Resource Material Englekir k. the the ends. Related . Visit www. India This release is a property of IIT Kanpur and BMTPC New (d) Delhi. they suffer severe local damage. weaker. August 2003 34 .IITK-BMTPC Earthquake Tip 17 How do Earthquakes Affect Reinforced Concrete Buildings? page 2 Horizontal Earthquake Effects are Different (which receive forces from columns) sh ould be Gravity loading (due to self weight and contents) on stronger than columns. USA.nicee. The level of bending moment due to damage can lead to collapse of a building. required on both faces of me mbers. to see previous IITK-BMTPC Earthquake Tips. Stretchi ng of member (b) Indian Concrete Code (IS 456.. although earthquake loading depends on severity of shaking columns at storeys above remain almost undamaged. steel bars are required on both faces of beams to resist reversals of Damage distributed All damage bending moment. Next Upcoming Tip Amount of How do Beams in RC Buildings Resist Earthquakes? tension Authored by: C. Earthquake Resistant Concrete (b) (c) Structures. Tension not fail so that beams can safely transfer force s to is generated at surfaces that stretch and compression columns and columns to foundation s. UK. and (c) Ductile Detailing Code for RC Structures (IS 13920. if columns are made the relative levels of this tension (in technical terms... and can exceed that due to gravity loading.org or www. Seismic Desig n of Reinforced and Precast Concrete Tension Building s. When beams beam in the central location and is at the top surface at are detailed properly to have large ductility. India Sponsored by: Building Materials and Technology Promotion Council. (b) Weak Columns. yielding of beams. John Wiley & S ons. earthquake loading causes building as a whole can deform by large amounts tension on beam and column faces at l ocati ons despite progressive damage caused due to consequent different from those under gravity loading (Figure 4c). connections between buildings causes RC frames to bend resulting in beams & columns and columns & foundati ons sh ould stretching and shortening at various locations.Murty Indian Institute of Technology Kanpur Kanpur. at those that shor ten (Figure 4b). Inc. (a) published the following Indian standards pertaining to design of RC frame buildings: (a) Indian Seismic Code (IS 1893 (Part 1). Thus. 1993) – for detailing requirements in seismic regions.org. New Delhi.R. at collaps e at collaps e Since concrete cann ot carry this tensi on. 1997. and Kappos.J.. On the other hand. I t may be reproduced without ch anging its conten ts Figure 4: Earthquake shaking reverses tension and with du e acknowled gemen t. 2000) – for design of and locati ons of tensi on Tension RC members. E&FN SPON. Damage under strong earthquake shaking.in. In contrast. and foundati ons Weak Beams Strong Beams Figure 5: Tw o distinct designs of buildings that result in different earthquake performances – Gravity Earthquak e columns should be stronger than beams. face. they act together as a frame transferring for ces faces (Figure 2b).e. Closed loop stirrups are provided from one to an other. Shear damage occurs are part of a building frame and carry earthquake. If relatively Longitudinal bars are provided to resist flexural less steel is present on the tension face. this is a brittle failure and is therefore undesirable. this is a ductile The Indian Ductile Detailing Code IS13920-1993 failure and hence is desirable.e. the amount of steel provided towards its mid-depth (Figure 2a). 35 . and going (b) At the ends of beams. the steel cracking on the side of the beam that stretches. the vertical and horizontal action. starting from the stretched beam face. the amount and distribution of steel to be provided Vertical Stirrup Smaller diameter steel in the beam must be determined by performing design bars that are made i nto Beam calculations as per is:456-2000 and IS13920-1993. more steel on prescribes that: tension face is not necessarily desirable! The ductile (a) At least two bars go through the full length of the failure is characterized with many vertical cracks beam at the top as well as the bottom of the beam. Learning 18 Earthquake Design Earthquake Tip and Construction How do Beams in RC Buildings Resist Earthquakes? Reinforcement and Seismic Damage (b) Shear Failure: A beam may also fail due to shearing In RC buildings. as both top and bottom faces stretch during strong steel has ability to stretch large amounts before it earthquake shaking (IITK-BMTPC Earthquake Tip 17). under the action of support and grows towards the top and bottom loads. namely: Figure 2: Tw o types of damage in a beam: (a) Flexural (or Bending) Failure: As the beam sags under flexure damage is preferred. resist the tension forces due to bending while If relatively more steel is present on the tension vertical stirrups resist shear forces. induced forces. closed l oops and are placed at regular Column Column intervals al ong the full length of the beam Beam Bottom fac e stretc hes in tension and vertical cracks dev elop (a) Flexure Failur e Column Inclined crack Longitudinal Bar Larger diameter steel bars that go through the full length of the beam Figure 1: Steel reinforcement in beams . the beams and columns) are built horizontal. namely: (a) long straight bars (called Design Strategy longitudinal bars) placed along its length. and (b) closed Designing a beam involves the selection of its loops of small diameter steel bars (called stirrups) material properties (i. Shear failure is brittle. grades of steel bars and concrete) placed vertically at regular intervals along its full and shape and size. Thus. And. Longitudinal bars increased loading.. Thus. these are usually selected as a par t length (Figure 1). This Tip is meant for beams that to avoid such shearing action.stirrups Beam 45 prevent longitudinal bars from bending outwards. of an overall design strategy of the whole building. snaps. Since yields first (it keeps elongating but does not snap. the concrete crushes in compression. shear failure Beams in RC buildings have two sets of steel must be avoided in the design of RC beams. concrete crushes in compression. and therefore. at the bottom is at least half that at top. it develops at mid-depth near the integrally with each other. when the area of these stirrups is insufficient. A shear crack is inclined at 45 to the members (i. it can fail in two possible ways. reinforcement. see IITK-BMTPC Earthquake Tip 9) and longitudinal steel bars are required on both faces at the redistribution occurs in the beam until eventually ends and on the bottom face at mid-length (Figure 3). (b) Shear F ailur e Beams sustain two basic types of failures. namely half the spacing mentioned in (c) above (Figure 5).Murty Indian Institute of Technology Kanpur Figure 4: Steel reinforcement in seismic beams Kanpur. India .org. the bars transfer large and with du e acknowled gemen t.M. USA. Thus. vertical stirrups sh ould be provided at a cl oser spacing (Figure 6). Third stirrups on stirrup Edition. an even more stringent in seismic beams – as per IS13920-1993. John Wiley & S ons. Suggestion s/co mmen ts forces from one to another.. India lengths of 12-14m.J. Prentice Hall.in..nicee. New Delhi. it must be at least 8mm. 1997. Related . At the location of the lap. Indian Standard Code of Practice for Ductile Detailing of Reinforced Concrete Structures Subjected to Seismic Forces. USA. 1992. Moreover. prescribes the following requirements related to stirrups in reinforced concrete beams: (a) The diameter of stirrup must be at least 6mm. (ii) they protect the 2d concrete from bulging outwards due to flexure.g. Reinforced Concrete Mechanics and Des ign. IS:13920-1993 prescribes that such laps of longitudinal September 2003 36 . and Bottom s teel at supp orts At least 2 bars should go (b) not made at locations where they are likely to at least half of that at top full length of beam stretch by large amounts and yield (e. New Delhi.IITK-BMTPC Earthquake Tip 18 How do Beams in RC Buildings Resist Earthquakes? page 2 bars are (a) made away from the face the column. (b) The spacing of vertical stirrups in any por tion of Lapping prohibited in the beam should be determined from calculations regions wh ere Column longitudinal bars can Column (c) The maximum spacing of stirrups is less than half yield in tension the depth of the beam (Figure 5).. Seismic Design of Masonry and 135 hooks i n 10 ti mes Reinforced Concrete Building s. bottom bars at mid-length of the beam).bmtpc.J. and Column Column (iii) they prevent the buckling of the compressed longitudinal bars due to flexure. d/2) Stirrups in RC beams help in three ways. Horizontal adjac ent Spacing diameter of McGregor.M. Tip 17: How do E arthquakes Affect Reinforced Concrete Buildings? Such s tirrups do not open during s trong Resource Material earthquake s haking.R. namely d (i) they carry the vertical shear force and thereby resist Beam 2d diagonal shear cracks (Figure 2b). Building Materials and Technology Promotion Steel reinforcement bars are available usually in Council.N. Bureau of Indian Standards.ac. to see previous IITK-BMTPC Earthquake Tips. spacing of stirrups is specified.stirrups with 135 hooks at ends required as per Sponsored by: IS:13920-1993. the Indian Standard IS13920-1993 spacing ensures good earthquake behaviour.. in Lapping of longitudinal bars beams more than 5m long.T.org or www. Earthquake Tip 135 Tip 9: How to Make Buildings Ductile for Good Seismic The ends of s tirrups Performance? are bent at 135 . IS 13920. Visit www. Spacing of stirrups (b) Both ends of the vertical stirrups should be bent not more than 150mm into a 135 hook (Figure 4) and extended Beam sufficiently beyond this h ook to ensure that the stirrup does not open out in an earthquake. Beam Spacing of stirrups Spacing of stirrups Total amount of steel as calculated as calculated Column from calculation Column (but not more than d/4 (but not more than d/4 and 8 times beam bar and 8 times beam bar Figure 3: Location and amount of longitudinal diameter) Spacing of stirrups diameter) as per calculations steel bars in beams – these resist tension due to (but not more than 2d 2d flexure. alternate si des 135º Next Upcoming Tip How do Columns in RC Buildings Resist Earthquakes? Authored by: C. the Indian Standard may be sent to: eqtip s@iitk. (d) For a length of twice the depth of the beam from Figure 6: Details of lapping steel reinforcement the face of the column. In moderate to severe Figure 5: Location and amount of vertical stirrups in beams – IS:13920-1993 limit on maximu m seismic zones. Thus. Preferr ed: Paulay. it becomes necessary to This release is a property of IIT Kanpur and BMTPC New overlap bars when beams of longer lengths are to be Delhi. I t may be reproduced without ch anging its conten ts made.V. and Priestley. (1993). at the locati ons of laps. Shear damage is brittle must be bent as 135 hooks (Figure 2). namely (i) they carry the horizontal shear forces long straight bars (called longitudinal bars) placed induced by earthquakes. and calculating amount and distribution of steel reinforcement. and thereby resist diagonal vertically along the length. and (b) closed l oops of shear cracks. Such hook ends and must be avoided in columns by providing prevent opening of loops and consequently buckling transverse ties at close spacing (Figure 2b). column within the cl osed loops. Columns can sustain two types of buckling). Learning 19 Earthquake Design Earthquake Tip and Construction How do Columns in RC Buildings Resist Earthquakes? Possible Earthquake Damage Vertical Bars tied together with Closed Ties Columns. Closely spaced horizontal cl osed ties help in three contain two types of steel reinforcement. of concrete and buckling of vertical bars. Columns that are required (a) Closely spaced ties must be provided at the two to resist earthquake forces must be designed to ends of the column over a length not less than prevent shear failure by a skillful selection of larger dimension of the column. Detailing Code IS:13920-1993 requires columns to be at least 300mm wide. column height or 450mm. grades of concrete and steel bars). namely: (a) ways. Suc h ti es that are made into closed bars that go through do not open during loops and are plac ed at Ties with the full height of the strong earthquake 10 ti mes regular intervals along the ends bent at 135 column shaking. and (iii) they contain the concrete in the damage.e. 135° hook ends in them causes brittle failure of during Design Strategy 2001 Bhuj Designing a column involves selection of m aterials earthquake to be used (i. (ii) they hold together the vertical bars smaller diameter steel bars (called transverse ties) and prevent them from excessively bending outwards placed horizontally at regular intervals along its full (in technical terms. this bending phenomenon is called length (Figure 1). namely axial-flexural (or combined compression. The ends of the ties bending) failure and shear failure. the vertical members in RC buildings. Figure 2: Steel reinforcement in seismic columns The first two aspects are part of the overall design – closed ties with 135 hooks are required as per strategy of the whole building. A column width of up to 200mm is The Indian Standard IS13920-1993 prescribes allowed if unsupported length is less than 4m and following details for earthquake-resistant columns: beam length is less than 5m. one-sixth the reinforcement. (b) choosing shape and size of the cross-section. diameter full hei ght of the column of tie 135 Vertical Spacing (a) Column Figure 1: Steel reinforcement in columns – closed Shear Failure Large spacing of ties at close spacing improve the performance of ties and lack of columns under strong earthquake shaking. Vertical bars Closed Ties The ends of ties are Smaller diameter steel bars Larger diameter steel bent at 135 . The Indian Ductile Indian Ductile Detailing Code IS:13920-1993. 37 . In columns where the spacing Spacing of ties in lap length between the corner bars exceeds 300mm. (c) The length of tie beyond the 135 bends must be at least 10 times diameter of steel bar used to make hc/4 the closed tie. USA.g.T. At other locations. India is about 50 times bar diameter. This spacing need not be less than 75mm nor more than 100mm. the vertical spacing of ties in columns should not exceed D/4 for where Spacing of ties not mor e than D/4. limitations in available length of bars and due to Next Upcoming Tip constraints in construction. to see previous IITK-BMTPC Earthquake Tips. These links need to go around both vertical bars and Spacing of ties not mor e than D/2 horizontal closed ties (Figure 3). there are numerous How do Beam-Column Joints in RC Buildings Resist Earthquakes? occasions when column bars have to be joined. ties are Beam spaced as per calculations but not more than D/2. New Delhi. in a not be l ess than 75mm nor At leas t larger of rectangular column. Bureau of Lapping Vertical Bars Indian Standards. special care is required to implement this properly at site. The lap length depends on types of Indian Institute of Technology Kanpur reinforcement and concrete. Suggestion s/co mmen ts provided along the length of the lap at a spacing not may be sent to: eqtip s@iitk. hc/4 Extra Li nks Beam At leas t larger of Spacing of ties D.. John Wiley & S ons. hc/6 and 450 mm more than 100 mm side). but need not be l ess than 75mm nor more than 100 mm D 180 lin ks around BOTH vertical bars Figure 4: Placing vertical bars and closed ties in and 135 ties columns – column ends and lap lengths are to be protected with closely spaced ties. the Indian Lapping of not mor e than s maller of vertical b ars Standard prescribes additional links with 180 hook D/2 and 150 mm in middle-half ends for ties to be effective in holding the concrete in of column its place and to prevent the buckling of vertical bars.IITK-BMTPC Earthquake Tip 19 How do Columns in RC Buildings Resist Earthquakes? page 2 (b) Over the distance specified in item (a) above and below a beam-column junction.J.in.org or www. Resource Material IS 13920. New Delhi. this extension beyond the bend should not be less than 75mm. India ends (Figure 4). Paulay. IS:13920-1993 Sponsored by: prescribes that the lap length be provided ONLY in the Building Materials and Technology Promotion middle half of column and not near its top or bottom Council. when laps are provided. and Priestley.Murty lap length. A simple way of achieving this is by overlapping the two Authored by: bars over at least a minimum specified length. 1992.N. but need D is the smallest dimension of the column (e. Delhi. Column Related . Seismic Design of Masonry and In the constructi on of RC buildings.V. I t may be reproduced without ch anging its conten ts Further. Also. it Kanpur. Indian Standard Code of Practice for Ductile Detailing of Reinforced Concrete Structures Subjected to Seismic Forces. only half the vertical bars in the This release is a property of IIT Kanpur and BMTPC New column are to be lapped at a time in any storey.nicee.R.. October 2003 38 . Spacing of ties not mor e than D/2 Construction drawings with clear details of closed ties are helpful in the effe ctive implementation at hc construction si te. For ordinary situati ons. Visit www.ac. due to the Reinforced Concrete Building s.bmtpc.org. hc/6 and 450 mm not mor e than D/4. Further. Earthquake Tip Figure 3: Extra links are required to keep the Tip17: How do E arthquakes Affect Reinforced Concrete Buildings? Tip18: How do Beams in RC Buildings Resist Earthquakes? concrete in place – 180 links are necessary to prevent the 135 tie from bulging outwards.. called C. ties must be and with du e acknowled gemen t. (1993). D is the length of the small D. more than 150mm.M. However. and beams loose their capacity to carry load. are applied during earthquakes. Indian Standard IS:13920-1993 balanced by bond stress developed between concrete recommends continuing the transverse loops ar ound and steel in the joint region. reinforcement (both longitudinal bars and stirrups) of all In such circum stances. joints are severely Reinforcing the Beam-Column Joint damaged. the bar slips inside the joint beams at a floor level to be prepared on top of the region. As explained in Ear thquake Tip 19. Under these j oints – such ties with 135 hooks resist the ill moments. IV and V to be at least in joint region: Large column width and good cracking and crushing 300mm wide in each direction of the cross-section concrete help in holding the of concrete when they support beams that are longer than 5m or beam bars when these columns are taller than 4m between floors Figure 2: Pull-push forces on j oints cause tw o (or beams). enough or if the strength of concrete in the joint is low. Thus. this is achieved by preparing the cage of the there is insufficient grip of concrete on the steel bars. thereby reducing the cracking and crushing of concrete. namely providing large column sizes and providing closely spaced closed-loop s teel ties around Beam-Column Joint column bars in the joint region (Figure 3). Repairing damaged joints is difficult. one diagonal length of the joint column joints (Figure 1). beam-column joints concrete in the joint region can be contr olled by two must be designed to resist earthquake effects. means. and so Problems of diagonal cracking and crushing of damage must be avoided. geometric distorti on. If the column is not wide the column bars through the joint region. 39 . the joints have limited column cross-se ctional size is insufficient. The American Concrete Institute problems – these result in irreparable damage in recommends a column width of at least 20 times the joints under strong seismic shaking. If the materials have limited strengths. diameter of largest longitudinal bar used in adjoining beam. In practice. beam formwork of that level and lowered into the cage (Figures 4a and 4b). Learning 20 Earthquake Design Earthquake Tip and Construction How do Beam-Column Joints in RC Buildings Resist Earthquakes? Why Beam-Column Joints are Special Further. Closed ties 10 ti mes Beam diameter of ti e Figure 1: Beam-Column Joints are critical parts 135º of a building – they need to be designed. These forces are some extra effort. this may not always be possible particularly when the beams are long and the Compression entire reinforcement cage becomes heavy. Since their constituent elongates and the other compresses (Figure 2b). The ties hold Overlap v olume common to beams together the concrete in the joint and also resist shear and columns force. Earthquake Behaviour of Joints Column Under earthquake shaking. portions of columns that are forces at top and bottom ends. When forces larger than these in the joint develops diagonal cracks. the top bars in the beam-column joint are effects of distortion of joints. pulled in one direction and the bottom ones in the Providing closed-loop ties in the joint requires opposite directi on (Figure 2a). under the action of the above pull-push In RC buildings. Gripping of bar inside Anchoring Beam Bars joint regi on Tension The gripping of beam bars in the joint region i s improved first by using columns of reasonably large cross-secti onal size. the concrete force carrying capacity. the Indian Standard IS:13920-1993 requires building (a) Loss of grip on beam bars (b) Distortion of joint: causes diagonal columns in seismic zones III. the beams adjoining a joint are subjected to moments in the same (clockwise Figure 3: Closed loop steel ties in beam-column or counter-clockwise) direction (Figure 1). joints undergo common to beams at their intersections are called beam. columns (Figure 5). Also. I t may be reproduced without ch anging its conten ts and with du e acknowled gemen t. 2002]. it is preferable are stack ed up. USA Photo from: The EERI Annotated Slid e CD. Bureau of Indian Standards. beam rei nforcement Shear failure of RC cage is lowered into beam-column joint the for mw ork during the 1985 Mexico City (c) Earthquak e. (2002). to see previous IITK-BMTPC Earthquake Tips. India already cast beam This release is a property of IIT Kanpur and BMTPC New (a) (b) Delhi. CA.nicee. these bars must be placed within the column bars and with no bends (Figure 6). a portion of beam top bar is embedded in the column IS 13920. but horizontal width is large. Suggestion s/co mmen ts Figure 5: Anchorage of beam bars in exterior may be sent to: eqtip s@iitk. and 98-2. November 2003.in. and when beam bars are of large diameter (Figure 5a).bmtpc. March 2005 40 . Visit www. It is difficult to hold such an overhanging SP 123.ac. American Concrete Institute. Building Code Requireme nts for Structural Concrete and Commentary. This length is measured Tip19: How do Columns in RC Buildings Resist Earthquakes? from the face of the column to the end of the bar Resource Material anchored in the column.org. American Concrete Institute. Beam bars bent in joi nt region overstress the c ore c oncrete adjoini ng the bends Column (a) Poor Practice Beam Beam Beam bars are within c olumn (b) bars and also str aight Stage II : Top bars of the beam Column are inserted i n the (b) Good Practice beam stirrups . (MI). and section column ties are c ontinued Figure 4: Providing horizontal ties in the j oints – (c) three-stage procedure is required. In interior joints. Stage III : when beam bars Ties in the joi nt region are are passed outside raised to their final locati ons. and a part of it Reinforced Concrete Structures Subjected to Seismic Forces. Farmington Hills.org or j oints – diagrams show elevation of joint region. Oakland. (1993). if column Beam top bars are not placed. The length of anchorage for a bar of grade Tip17: How do E arthquakes Affect Reinforced Concrete Buildings? Fe415 (characteristic tensile strength of 415MPa) is Tip18: How do Beams in RC Buildings Resist Earthquakes? about 50 times its diameter. India Sponsored by: Portion of top beam Building Materials and Technology Promotion bar below soffit of the Portion of colu mn Council.V. New Delhi. USA. USA. Such an approach has been used in the American practice [ACI318M. the beam bars may not extend below ties in the j oint region the soffit of the beam (Figure 5b). longitudinal beam bars need to be anchored into the column to ensure proper gripping of Related . Design of Beam-Column Joints for Seismic Resistance. Indian Standard Code of Practice for Ductile Detailing of that is cast up to the soffit of the beam. Earthquake Tip bar in joint. On the other hand.R. In columns of small widths ACI 318M. New Delhi. Special Narro w Column W ide Column Publication. Thus. overhangs. www. 1991 Next Upcoming Tip Approxim ately 50 times b ar diam eter Why are Open-Ground Storey Buildings Danger ous in Earthquakes? L-shaped bar ends ACI 318M-2002 Practice Authored by: C. the beam bars (both top and bottom) need to go through the joint without any cut in the joint region.Murty Indian Institute of Technology Kanpur Kanpur. to have columns with sufficient width. the c olumn cross- tied with binding wire. EERI. Figure 6: Anchorage of beam bars in interior j oints – diagrams (a) and (b) show cross- In exterior joints where beams terminate at sectional views in plan of joint region.IITK-BMTPC Earthquake Tip 20 How do Beam-Column Joints in RC Buildings Resist Earthquakes? page 2 beam top bar in positi on while casting the column up Temporary prop (a) Stage I : to the soffit of the beam. or if they do n ot have adequate ductility (See IIT- An open ground storey building. i. and the columns in the open ground storey are severely Figure 1: Ground storeys of reinforced concrete stressed (Figure 2b). Such buildings hundred RC frame buildings with open ground are often called open ground storey buildings or buildings storeys at Ahmedabad (~225km away from epicenter) on stilts. Thus. but it could Stiff upper storeys: be at any other storey level too. and most of the horizontal displacement of the building occurs in the soft ground storey itself. (b) It is relatively weak in ground storey. Thus. 1999 Taiwan and 2003 Algeria earthquakes). have two distinct of the building (Figure 3b). the upper storeys move almost together as a single block.. The presence of walls in upper storeys makes them much stiffer than the open ground storey. Further. Thus.500 eleven-storey buildings. characteristics. columns in the in moderate to severe seismic zones (namely III. the soft or weak storey usually exists at the ground storey level. the relative horizontal displacement it undergoes in the Earthquak e ground storey is much larger than what each of the oscillations storeys above it does.. a such buildings constructed in recent times have a huge number of similarly designed and constructed special feature – the ground storey is left open for the buildings exist in the various towns and cities si tuated purpose of parking (Figure 1). the total horizontal earthquake for ce it can carry in the ground storey is significantly smaller than what each of the storeys above it can carry.000 five-storey Reinforced concrete (RC) frame buildings are buildings and about 1. For instance. this type of buildings can be explained as a building on chopsticks. In common language. Small displac ement between adjac ent floors Earthquake Behaviour Open ground storey buildings have consistently Soft ground storey: shown poor performance during past earthquakes Large displ acement between foundation and first fl oor across the world (for example during 1999 Turkey. becoming increasingly common in urban India. Learning 21 Earthquake Design Earthquake Tip and Construction Why are Open-Ground Storey Buildings Vulnerable in Earthquakes? Basic Features Ahmedabad alone has about 25. even though their ground storey may Pendulum be soft and weak. a significant (b) Ground storey col umns sev erely stress ed number of them have collapsed. such buildings swing back-and-forth like inverted pendulums during earthquake shaking (Figure 2a). they may be severely columns in the ground storey and both partiti on walls damaged (Figure 3a) which may even lead to collapse and columns in the upper storeys. during the 2001 Bhuj earthquake has emphasised that such buildings are extremely vulnerable under earthquake shaking. open ground storey buildings are called soft Inverted (a) storey buildings.. having only BMTPC Earthquake Tip 9). the city of such buildings are like inverted pendulums. i. the open ground storey may also be a weak storey.e.e. IV ground storey do not have any partition walls (of and V) of the country.e. Many majority of them have open ground storeys. Generally. This flexible ground storey is also called soft storey. namely: (a) It is relatively flexible in the ground storey. Often. A large number of Figure 2: Upper storeys of open ground storey buildings with open ground storey have been built in buildings move together as a single block – India in recent years. If the columns are weak (do not buildings are left open to facilitate parking – have the required strength to resist these high stresses) this is common in urban areas in India. 41 . The collapse of more than a either masonry or RC) between them. i. (b) 2001 Bhuj Earthquake Figure 3: Consequences of open ground storeys in RC frame buildings – severe damage to ground storey columns and building collapses. it specifies when a This release is a property of IIT Kanpur and BMTPC New Delhi.org.ac. Earthquake Tip Tip 6: How Architectural Features Affect Buildings During Infill walls not Earthquakes? considered i n Tip17: What are the Earthquake Effects on Reinforced Concrete upper storeys Buildings? Resource Material IS 1893(Part 1) (2002). it would be ideal to build walls (either masonry or RC walls) in the ground storey also (Figure 5). For all new RC frame buildings. stiff masonry Figure 5: Av oiding open ground storey problem – walls (Figure 4a) are neglected and only bare frames are continuity of walls in ground storey is preferred. the drop in stiffness and strength in the ground storey level is not abrupt due to the absence of infill walls.in. 1998. effects of flexible and weak ground storeys by (a) 1971 San Fernando Earthquake ensuring that too many walls are not discontinued in the ground storey. the best option i s to avoid such sudden and large decrease in stiffness and/or strength in any storey.org or forces for the soft storey as compared to the rest of the www. New Delhi. India Improved design strategies Sponsored by: After the collapses of RC buildings in 2001 Bhuj Building Materials and Technology Promotion earthquake. Thus. The Code suggests that the forces in the columns. i. The existing open ground storey buildings need to be strengthened suitably so as to prevent them from collapsing during strong earthquake shaking.R.. Firstly. However.e. Indian Institute of Technology Kanpur Kanpur. Next Upcoming Tip (a) Actual building (b) Building being assum ed Why are short columns more damaged during earthquake s? in current design pr actice Figure 4: Open ground storey building – Authored by: assumptions made in current design practice C. Indian Standard Code of Practice for Criteria for Design of Earthquake Resistant Structures. I t may be reproduced without ch anging its conten ts building should be considered as a soft and a weak and with du e acknowled gemen t. may be obtained by considering the bare frame building (without any infills) (Figure 4b).IITK-BMTPC Earthquake Tip 21 Why are Open-Ground Storey Buildings Vulnerable in Earthquakes? page 2 structure.5 times the forces obtained from this bare frame analysis. The owners should seek the services of qualified structural engineers who are able to suggest appropriate solutions to increase seismic safety of these buildings. beams and shear walls (if any) under the action of seismic l oads spe cified in the code. Bureau of Indian Standards. December 2003 42 . the Indian Seismic Code IS:1893 (Part 1) - 2002 has included special design provisions related to Council. Suggestion s/co mmen ts storey building. beams and columns in the open ground storey are required to be designed for 2.bmtpc.nicee. New Delhi. Designers can avoid dangerous Photo Courtesy: The EERI Annotate d Slid e Set CD.Murty are not consistent with the actual structure. Direct flow of forces through w alls The Problem Open ground storey buildings are inherently poor systems with sudden drop in stiffness and strength in the ground storey. India soft storey buildings. Earthquak e Engin eeri ng Res earch Institute. Related . Visit www. the inverted pendulum effect is not captured in design. to see previous IITK-BMTPC Earthquake Tips. Oaklan d (CA). it specifies higher design may be sent to: eqtip s@iitk. USA. In the current practice.V. Secondly. considered in design calculati ons (Figure 4b). the short column deform over the full height. As a result. When a building is rested on sloped ground within one storey. Consider a wall (masonry or RC) of partial height built to fit a window Regular Short over the remaining height. a tall column and a shor t full amount over the short height adjacent to the column of same cross-section move horizontally by window opening. see IITK-BMTPC Ear thquake Tip 17). Short Portion of column restrained Long from Tall Column: Attracts s maller moving Short Column: horizontal force Attracts l arger horizontal force Figure 3: Short columns effect in RC buildings Figure 2: Short columns are stiffer and attract w hen partial height walls adj oin columns – larger forces during earthquakes – this must the effect is implicit here because infill walls be accounted for in design. regular columns same amount (Figure 2). 43 . When the floor slab moves horizontally during Figure 1: Buildings w ith short columns – two an earthquake. Two examples of buildings with shor t floor slab at a particular level (this is called rigid floor columns are sh own in Figure 1 – buildings on a diaphragm action. However. other columns in the same storey Column Sloped Ground are of regular height. the stiff walls restrict horizontal m ovement of the Poor behaviour of sh ort columns is due to the fact lower portion of a short column. are often treated as non-structural elements. during earthquake shaking all columns shorter columns as compared to taller columns in the move horizontally by the same amount along with the same storey. Since the effective height is stiffer as compared to the tall column. If a shor t regular column. short and tall columns exist wi thin the same storey level. reinforced concrete (RC) Many situations with short column effect arise in frame buildings that have columns of different heights buildings. Learning 22 Earthquake Design Earthquake Tip and Construction Why are Short Columns more Damaged During Earthquakes? Which Columns are short? The Short Column Behaviour During past earthquakes. short column sustains column is not adequately designed for such a large more damage. and it attracts over which a sh ort column can freely bend is small. it larger earthquake force. The adjacent columns Column Column behave as short columns due to presence of these Tall walls. The damage in these short columns is often in Partial Short Regular the form of X-shaped cracking – this type of damage of Height column Opening Wall Column columns is due to shear f ailure (see IITK-BMTPC Earthquake Tip 19). However. Figure 4 shows X-cracking in a column force. If sloping ground and buildings with a mezzanine floor. as there are no walls adjoining them. earthquake. then the short columns attract several times (b) larger earthquake force and suffer more damage as Mezzanine compared to taller ones. and it deforms by the that in an earthquake. Floor The short column effect al so occurs in columns that support mezzanine floors or l oft slabs that are (a) added in between two regular floors (Figures 1b). thereby attracts a larger force as compared to the larger is the force required to de form it. suffered more damage in the (Figure 1a). the upper ends of these columns explicit examples of common occurrences. On the other hand. undergo the same displacement (Figure 3). In many cases. it can suffer significant damage during an adjacent to the walls of partial height. Stiffness of a column means offers m ore resistance to horiz ontal moti on and resistance to deformation – the larger is the stiffness. This behaviour is called Short Column Effect. There is another spe cial situation in buildings when short-column effect occurs. Where walls of partial height are Sponsored by: present. New Delhi. different Indian Institute of Technology Kanpur retrofit solutions can be employed to avoid damage in Kanpur. Earthquake Tip Tip 6: How Architectural Features Affect Buildings During short columns. short column effect should be IS:13920-1993 for the short columns.ac.IITK-BMTPC Earthquake Tip 22 Why are Short Columns more Damaged During Earthquakes? page 2 Length depends on diameter of longitudinal bar Regular floor transverse confining ties. short This release is a property of IIT Kanpur and BMTPC New columns need to be strengthened using one of the well Delhi. closely spaced closed ties) must extend beyond the short column into the columns vertically above and Next Upcoming Tip Why are buildings with shear walls preferred in seismic regions? below by a certain distance as shown in Figure 5.Murty In existing buildings with short columns.org.in.. and sill of McGraw Hill Bo ok Comp any. transverse confining ties Closely spac ed s peci al throughout the height Closely spac ed s peci al and into column abov e Mezz anine floor only at end s Short column Source: between lintel Wakabayas hi. the simplest solution is to close the openings Building Materials and Technology Promotion by building a wall of full height – this will eliminate Council. Reinforced Concrete Structures Subjected to Seismic Forces. Visit www.V. India the short column e ffect. If that is not possible. this effect must be addressed in Earthquakes? structural design.org or with requisite background. When it is not possible to avoid Related .R. New Delhi. (1993). See IITK-BMTPC Earthquake Tip 19 for details of the special Authored by: confinement reinforcement. I t may be reproduced without ch anging its conten ts established retrofit techniques. to see previous IITK-BMTPC Earthquake Tips. New York. window USA Figure 4: Effectiv e height of column over w hich it can bend is restricted by adj acent walls – this short-column effect is most severe when Short Column Regular Column opening height is small. The Indian Standard IS:13920-1993 Tip 17: How do E arthquakes Affect Reinforced Concrete Buildings? for ductile detailing of RC structures requires special Tip 19: How do Columns in RC Buildings Resist Earthquakes? confining reinforcement to be provided over the full Resource Material height of columns that are likely to sustain short IS 13920.e. Figure 5: Details of reinforcement in a building w ith short column effect in some columns – The Solution additional special requirements are given in In new buildings.bmtpc. Indian Standard Code of Practice for Ductile Detailing of column effect. avoided to the extent possible during architectural design stage itself. India future earthquakes.M. Desig n of Earthquak e-Res istant Buil din gs. Suggestion s/co mmen ts should be designed by a qualified structural engineer may be sent to: eqtip s@iitk. January 2004 44 . C. The retrofit solution and with du e acknowled gemen t. The special confining reinforcement (i.. www. Bureau of Indian Standards.nicee. Shear walls are usually provided along both buildings in the direction of their orientati on. Shear walls significantly reduces lateral sway of the building and are like vertically-oriented wide beams that carry thereby reduces damage to structure and its contents. These walls Most RC buildings with shear walls also have generally start at foundation level and are continuous columns. Shear walls should be provided along preferably both length and width.” shear walls :: Mark Fintel. but their size must be small to ensure least interruption to force flow through walls. Their thickness can be (i. Shear walls are more Properly designed and detailed buildings with effective when located along exterior perimeter of the shear walls have shown very good performance in past building – such a layout increases resistance of the earthquakes. However. because reinforcement detailing of walls is relatively straight-forward and therefore easily implemented at site. (Figure 2). 45 .. Thus. both in terms of constructi on cost and effectiveness in Figure 2: Shear walls must be symmetric in plan minimizing earthquake damage in structural and non. They could be placed symmetrically along Advantages of Shear Walls in RC Buildings one or both dire ctions in plan.e. or as high as 400mm in high rise Shear walls provide large strength and stiffness to buildings. design of their foundations requires special attention. vertical plate-like RC walls called Shear Walls (Figure 1) Architectural Aspects of Shear Walls in addition to slabs. these columns primarily carry gravity loads throughout the building height. even plan about both axes buildings with sufficient amount of walls that were not specially detailed for seismic performance (but had Symmetric lo cation of enough well-distributed reinforcement) were saved shear walls along the perimeter of the from collapse. if they are provided along only one direction. Learning 23 Earthquake Design Earthquake Tip and Construction Why are Buildings with Shear Walls Preferred in Seismic Regions? What is a Shear Wall Building structural elements (like glass windows and building Reinforced concrete (RC) buildings often have contents). those due to self-weight and contents of building). Shear wall buildings are a popular building is d esir able choice in many earthquake prone countries. The overwhelming success of buildings building to twisting. earthquake loads downwards to the foundation. in past earthquakes. Special RC design checks are required to ensure that the net cross- Foundation Shear sectional area of a wall at an opening is sufficient to W all carry the horizontal earthquake force. openings should be symmetrically located. Shear walls are efficient. beams and columns. with shear walls in resisting strong earthquakes is summarised in the quote: “We cannot afford to build concrete buildings meant Unsymmetric location of to resist severe earthquakes without shear walls. Shear walls are easy to construct. Plan Door or window openings can be provided in shear walls. the overturning effects on them are large. a proper grid of beams and RC Walls columns in the vertical plane (called a moment-resistant frame) must be provided along the other direction to resist strong earthquake effects. Figure 1: Reinforced concrete shear walls in buildings – an excellent structural system for Shear walls in buildings must be symmetrically located in plan to reduce ill-effects of twist in buildings earthquake resistance. New Zealand and USA. However. like Chile. a noted consulting engineer in USA not desirable Shear walls in high seismic regions require special Symmetry of building in detailing. Moreover. layout – twist in buildings can be avoided. Since shear walls carry large horizontal earthquake forces. which length and width of buildings (Figure 1). as low as 150mm. India reinforced in a special manner to sustain these load Sponsored by: reversals without loosing strength (Figure 4b). While elem ents rectangular cross-secti on is common. Suggestion s/co mmen ts Earthquake Tip 19). Reinforcement Bars in RC Walls: Steel reinforcing bars are to be provided in walls in Related .N. Overall geometric proportions susceptible to earthquake damage than walls without of the wall. Horizontal reinforcement needs to be IS 13920.M.IITK-BMTPC Earthquake Tip 23 Why are Buildings with Shear Walls Preferred in Seismic Regions? page 2 Ductile Design of Shear Walls increased. to see previous IITK-BMTPC Earthquake Tips.bmtpc. edges Authored by: of shear walls experience high compressive and tensile C. The Indian Standard Ductile Detailing Code for RC members Tension Compressi on (IS:13920-1993) pr ovides special design guidelines for ductile detailing of shear walls. RC walls with boundary elements have Just like reinforced concrete (RC) beams and substantially higher bending strength and horizontal columns.in. New Delhi. Sometimes.J. Visit www. RC shear walls also perform much better if shear force carrying capacity. closel y s pac ed ti es boundary element Rectangular (b) Figure 3: Shear walls in RC Buildings – different Figure 4: Layout of main reinforcement in shear walls as per IS:13920-1993 – detailing is the geometries are possible. along each of the horizontal and Paulay.and U-shaped Proper anc horing of v ertical sections are also used (Figure 3)..e. key to good seismic performance. Indian Standard Code of Practice for Ductile Detailing of anchored at the ends of walls. Bureau of reinforcing steel to be provided is 0. (1992).. i.org. types and am ount of reinfor cement. and should be taken advantage of to resist earthquake forces..Murty stresses. and are therefore less designed to be ductile. The vertical and horizontal reinfor cement in the Tip 19: How do Columns in RC Buildings Resist Earthquakes? wall can be placed in one or two parallel layers called Resource Material curtains. (a) C-Shaped Boundary Boundary Elements L-Shaped Elem ent without increased thickness Boundary Elements Boundary with incr eased thickness Elem ent RC Hollow Core around Elevators Confining reinforcement in Anchoring of wall boundary elements: reinforcement in 135 hooks. USA vertical directions. concrete in the wall end regions must be Kanpur. This vertical reinforcement should be distributed uniformly across the wall cross-section.0025 times the Indian Standards.T. End Building Materials and Technology Promotion regions of a wall with increased confinement are called Council. (1993). shear wall in these boundary elements is also February 2004 46 . I t may be reproduced without ch anging its conten ts provided in columns of RC frames (See IITK-BMTPC and with du e acknowled gemen t. To ensure that shear walls behave in a ductile Indian Institute of Technology Kanpur way. Next Upcoming Tip How to Reduce Earthquake Effects on Buildings? Boundary Elements: Under the large overturning effects caused by horizontal earthquake forces. Seismic Desig n of Reinforce d Concrete and Masonry Buildings. Thin-walled hollow reinforcement into foundation RC shafts ar ound the elevator core of buildings also act as shear walls. This special confining transverse This release is a property of IIT Kanpur and BMTPC New reinforcement in boundary elements is similar to that Delhi.ac. India boundary elements. New Delhi. the thickness of the may be sent to: eqtip s@iitk. and Priestley. L.org or www. connection with remaining elements in the building help in improving the ductility of walls. Earthquake Tip regularly spaced vertical and horizontal grids (Figure Tip 6: How Architectural Features Affect Buildings During Earthquakes? 4a). cross-secti onal area.R. The minimum area of Reinforced Concrete Structures Subjected to Seismic Forces. and boundary elements.nicee. J ohn Wiley & S ons. one dimension of the reinforcem ent in boundary cross-secti on is much larger than the other. Overall Geometry of Walls: Shear walls are Closely spaced confining oblong in cross-se ction.V. like hospital s. and many of lesser – this technique is called Base Isolation. These are (a) Hypothetical Base Isolation Devices and Seismic Dampers. whereas Forces induced are large. This may render the building suitable for all buildings. the ground moves under Two basic technol ogies are used to protect the building. Several commercial brands of Figure 1: Building on flexible supports shakes base isolators are available in the market. Small or at least greatly reduced. the for ces Building on flexible pads connected to building induced by ground shaking can be a few times smaller and foundation – building will shake less than that experienced by the building built directly on ground. However. When the ground shakes. buildings such that they remain practically If the gap between the undamaged even in a severe earthquake. A careful study is shaking. no Flexible force is transferred to the building due to shaking of Material the ground. The flexible pads are called base-isolators. which on hard soil underneath. Most suitable candidates for non-functi onal after the earthquake. although there are Conventional seismic design attempts to make other types that are based on sliding of one part of the buildings that do not collapse under strong earthquake building relative to the other. but may sustain damage to non-structural required to identify the most suitable type of device elements (like glass facades) and to some structural for a particular building. Thus. Now. high-rise buildings or need to remain functional in the aftermath of the buildings rested on soft soil are not suitable for base earthquake. Large mov ement the structures pr otected by means of these devices are of building called base-isolated buildings. Large (much like the way shock absorbers in motor vehicles mov ement Flexible pad s absorb the impacts due to undulations of the road). in isolators Base Isolation The concept of base isolati on is explained through an example building resting on frictionless rollers Original (Figure 1a). This helps in further reducing the seismic response of the building. the rollers freely Lead pl ug Isolator roll. if the same building is rested on Stainless steel plates flexible pads that offer resistance against lateral movements (Figure 1b). The main feature of the base isolation technology is that it introduces flexibility in the structure. Buildings building and v ertical wall of the foundation pit is s mall. As a result. Also. Special techniques are required to design isolation. namely a fixed base building (Figure 1c). this cost is may hit the building. but the building above does not move. the building does not experience the earthquake. The isolators are often Building resting directly on ground designed to absorb energy and thus add damping to – building will shake violently the system. Learning 24 Earthquake Design Earthquake Tip and Construction How to Reduce Earthquake Effects on Buildings? Why Earthquake Effects are to be Reduced them look like large rubber pads. If Building the flexible pads are properly chosen. w hen justified through improved earthquake performance. with such improved seismic per formance usually cost the v ertical wall of the pit Rollers more than normal buildings do. The idea Building behind base isolation is to detach (isolate) the building Building on rollers without any friction from the ground in such a way that earthquake – building will not move with ground motions are not transmitted up through the building. which may be base-isolation are low to medium-rise buildings rested problematic in some structures. then some effect of the ground (b) Base Isolated Isolator during Earthquake shaking will be transferred to the building above. Seismic dampers are special Forces induced can be up to mov ement devices introduced in the building to absorb the 5-6 ti mes s maller than those in a regular building resti ng of building energy provided by the ground motion to the building directly on ground. buildings from damaging earthquake effects. 47 . simply. base isolation is not members in the building. a r obust (c) Fixed-Base medium-rise masonry or reinforced concrete building Building becomes extremely flexible. G. the four-storey Bhuj Hospital building was built with base isolation Bolt technique (Figure 2).H.bmtpc.D.R.. These dampers act Hanson.R. (1999)..nicee. Oakland (CA).I. Base isolation has now been used in Fluid numerous buildings in countries like Italy. However. In India. technology.W. such as diagonal braces.com/main.htm. An and only little is transmitted above to the chassis of the Introduction to Seismic Isolation. car. I t may be reproduced without ch anging its conten ts them rubbing against each other). Two single storey buildings (one school building and another shopping complex building) in newly relocated Killari town were built Steel with rubber base isolators resting on hard ground..ac. and yielding dampers and with du e acknowled gemen t..org/reading s/EERI_Report. Suggestion s/co mmen ts (energy is absorbed by metallic components that yield) may be sent to: eqtip s@iitk. By now. USA. original District Hospital building at Bhuj Related . USA. to see previous IITK-BMTPC Earthquake Tips. (1999). John Wiley & Sons.nicee. USA (b) Friction Damper Yield loc ation of metal Basement c olumns Base Isolator (c) Yielding Dampers supporting bas e isol ators Figure 3: Seismic Energy Dissipation Devices – Figure 2: View of Basement in Bhuj Hospital building – built with base isolators after the each device is suitable for a certain building. New Zealand. friction dampers have been www. and McVerry. (2001).org or (Figure 3). India between piston-cylinder arrangement).H.T. base isolation technique was first demonstrated after the 1993 Killari (Maharashtra) (a) Viscous Damper Earthquake [EERI. and USA. Visit www. that they were used to protect Kanpur. It has been in increased use since the 1980s. In India.V. Earthquake Engineering the sudden jerks are absorbed in the hydraulic fluids Research Institute. Robinson. EERI. Tip 5: What are the Seismic Effects on Structures? Tip 8: What is the Seismic Design Philosophy for Buildings? Seismic Dampers Resource Material Another approach for contr olling seismic damage EERI. Earthquake Tip collapsed during the 2001 Bhuj earthquake. When seismic energy is transmitted through them. New Delhi. Base isolation is also useful for retrofitting important buildings (like hospitals and historic buildings). Dampers were used since 1960s to C.htm).palldynamics. Earthquake Engineering Research Institute.Murty protect tall buildings against wind effects. it Indian Institute of Technology Kanpur was only since 1990s.IITK-BMTPC Earthquake Tip 24 How to Reduce Earthquake Effects on Buildings? page 2 Base Isolation in Real Buildings provided in a 18-storey RC frame structure in Gurgaon Seismic isolation is a relatively recent and evolving (See http://www. Japan. and Soong. Lessons Learnt Over Time – Learning from Earthquakes in buildings and improving their seismic performance Series: Volume II Innovative Recovery in Ind ia. Commonly used Sponsored by: types of seismic dampers include viscous dampers Building Materials and Technology Promotion (energy is absorbed by silicone-based fluid passing Council.. and has been well evaluated and reviewed Viscous internationally.T. elements. over 1000 buildings across Piston the world have been equipped with seismic base isolation. March 2004 48 . New York. also is by installing seismic dampers in place of structural available at http://www.in. 1999]. Oakland (CA). After the 2001 Bhuj (Gujarat) earthquake. friction dampers This release is a property of IIT Kanpur and BMTPC New (energy is absorbed by surfaces with friction between Delhi. Photo Courtesy: Marjori e Greene. Seismic Design with like the hydraulic shock absorbers in cars – much of Supplemental Energy Dissipation Devices.org. and thus damp the motion of Authored by: the building.R. dampers absorb part of it. Both Plate were brick masonry buildings with concrete roof. India buildings against earthquake effects. Skinner. Minor Shaking Moderate Shaking Strong Shaking For more information.nicee. Fax: (0512) 259 7794 Email:
[email protected] . please contact: Coordinator National Information Center of Earthquake Engineering Indian Institute of Technology Kanpur Kanpur 208016 Phone: (0512) 259 7866.in. Web: www.