National Structural Code of the Philippines Sections 407.1 ± 407.9 Details of Reinforcement 407.1 Notations d = distance from extreme compression fiber to centroid of tension reinforcement, mm db = nominal diameter of bar, wire or prestressing strand, mm fci = compressive strength of concrete at time of initial prestress, Mpa fy = specified yield strength of nonprestressed reinforcement, Mpa Ld = development length, mm. See Section 412. 407.2 Standard Hooks ³Standard Hook´ as used in this code is one of the following: 407.2.1 180-degree bend plus 4db extension, but not less than 60 mm at free end of bar. 407.2.2 90-degree bend plus 12db extension at free end of bar. 407.2.3 For stirrup and tie hooks: 1. 16 mm bar and smaller, 90-degree bend plus 6db extension at free end of bar; or 2. 20 mm and 25 mm bar, 90-degree bend, plus 12db extension at free end of bar; or 3. 25 mm bar and smaller, 135-degree bend plus 6db extension at free end of bar 407.2.4 Seismic hooks as defined in Section 402. 407.3 Minimum Bend Diameters 407.3.1 Diameter of bend measured on the inside of the bar, other than for stirrups and ties in sizes 10 mm through 16 mm, shall not be less than the values in Table 407 ± 1. 407.3.2 Inside diameter of bends for stirrups and ties shall not be less then 4db for 16 mm bar and smaller. For bars larger than 16 mm, diameter of bend shall be in accordance with Table 407 ± 1. 407.3.3 Inside diameter of bends in welded wire fabric (plain or deformed) for stirrups and ties shall not be less than 4db for deformed wire larger than MD40 and 2db for all other wires. Bends with inside diameter of less than 8db shall not be less than 4db from nearest welded intersection. Table 407 ± 1 ± Minimum Diameters of Bend Bar Size 10 mm through 25 mm 28 mm, 32 mm and 36 mm 42 mm and 58 mm Minimum Diameter 6db 8db 10db 407.4 Bending of Reinforcement 407.4.1 All reinforcement shall be bend cold, unless otherwise permitted by the engineer-ofrecord. 407.4.2 Reinforcement partially embedded in concrete shall not be field bent, except as shown on the design drawings or permitted by the engineer-of-record. 407.5 Surface Conditions of Reinforcement 407.5.1 At the time concrete is placed, reinforcement shall be free from mud, oil or other nonmetallic coatings that decrease bond. Epoxy coatings of steel reinforcement in accordance with Sections 403.6.3.8 and 403.6.3.9 shall be permitted. 407.5.2 Reinforcement, except prestressing tendons, with rust, mill scale or a combination of both, shall be considered satisfactory, provided the minimum dimensions (including height of deformations) and weight of a hand-wire-brushed test specimen comply with applicable ASTM specifications referenced in Section 403.6. 407.5.3 Prestressing tendons shall be clean and free of oil, dirt, scale, pitting and excessive rust. A light coating of rust shall be permitted. 407.6 Placing Reinforcement 407.6.1 Reinforcement, prestressing tendons and ducts shall be accurately placed and adequately supported before concrete is placed, and shall be secured against displacement within tolerances of this section. 407.6.2 Unless otherwise specified by the engineer-of-record, reinforcement, prestressing tendons and prestressing ducts shall be placed within the following tolerances: 407.6 Placing Reinforcement 407.6.2.1 Tolerance for depth d, and minimum concrete cover in flexural members, walls and compression members shall be as follows: Effective depth, d Tolerance on d Tolerance on Minimum Concrete Cover -10 mm -12 mm d 200 mm d 200 mm ± 10 mm ± 12 mm except that tolerance for the clear distance to formed soffits shall be minus 6 mm and tolerance for cover shall not exceed minus one-third the minimum concrete cover required by the approved plans or specifications. 407.6 Placing Reinforcement 407.6.2.2 Tolerance for longitudinal location of bends and ends of reinforcement shall be ±50 mm except at discontinuous ends of members where tolerance shall be ±12 mm at the discontinuous ends of brackets and corbels, and ±25 mm at the discontinuous ends of other members. The tolerance for concrete cover of Section 407.6.2.1 shall also apply at the discontinuous ends of members. 407.6.3 Welded wire fabric (with wire size not greater than MW30 or MD30) used in slabs not exceeding 3 m in span shall be permitted to be curved from a point near the top of slab over the support to a point near the bottom of slab at midspan, provided such reinforcement is either continuous over, or securely anchored at, support. 407.6 Placing Reinforcement 407.6.4 Welding of crossing bars shall not be permitted for assembly of reinforcement. Exceptions: 1. Reinforcing steel bars are not required by design. 2. When specifically approved by the engineer-ofrecord, welding of crossing bars for assembly purposes in Seismic Zone 2 may be permitted, provided that data are submitted to the engineer to show that there is no detrimental effect on the action of the structural member as a result of welding of the crossing bars. 407.7 Spacing Limits for Reinforcement 407.7.1 The minimum clear spacing between parallel bars in a layer shall be db but not less than 25 mm. See also Section 403.4.2. 407.7.2 Where parallel reinforcement is placed in two or more layers, bars in the upper layers shall be placed directly above bars in the bottom layer with clear distance between layers not less than 25 mm. 407.7.3 In spirally reinforcement or tied reinforced compression members, clear distance between longitudinal bars shall not be less than 1.5db or less than 40 mm. See also Section 403.4.2. 407.7 Spacing Limits for Reinforcement 407.7.4 Clear Distance limitation between bars shall apply also to the clear distance between a contact lap splice and adjacent splices or bars. 407.7.5 In walls and slabs other than concrete joist construction, primary flexural reinforcement shall not be spaced farther apart than three times the wall or slab thickness, nor farther than 450 mm. 407.7 Spacing Limits for Reinforcement 407.7.6 Bundled Bars 407.7.6.1 Groups of parallel reinforcing bars bundled in contact to act as a unit shall be limited to four bars in one bundle. 407.7.6.2 Bundled bars shall be enclosed within stirrups or ties. 407.7.6.3 Bars larger than 36 mm shall not be bundled in beams. 407.7.6.4 Individual bars within a bundle terminated within the span of flexural members shall terminate at different points with at least 40db stagger. 407.7.6.5 Where spacing limitations and minimum concrete cover are based on bar diameter db, a unit of bundled bars shall be treated as a single bar of a diameter derived from the equivalent total area. 407.7 Spacing Limits for Reinforcement 407.7.7 Prestressing Tendons and Ducts 407.7.7.1 Center-to-center spacing of pre-tensioning tendons at each end of a member shall not be less than 5db for wire, nor 4db for strands, except that if concrete strength at transfer of prestress, fci is 28 MPa or more, minimum center to center spacing of strands shall be 45 mm for strands of 12 mm nominal diameter or smaller and 50 mm strands of 16 mm nominal diameter. See also Section 403.4.2. Closer vertical spacing and bundling of tendons shall be permitted in the middle portion of a span. 407.7.7.2 Bundling of post-tensioning ducts shall be permitted if it is shown that concrete can be satisfactory placed and if provisions is made to prevent the tendons, when tensioned, from breaking through the duct. 407.8 Concrete Protection for Reinforcement 407.8.1 Cast-in-Place Concrete (Nonprestressed) Unless a greater cover is required by Section 407.8.6 or 407.8.8, specified cover for reinforcement shall not be less than the following: 1. 2. 3. a) b) c) Minimum Cover Concrete cast against and permanently exposed to earth ............... 75 mm Concrete exposed to earth or weather: 20 mm bar through 36 mm bar .................................................. 50 mm 16 mm bar, MW200 or MD200 wire, and smaller ....................... 40 mm Concrete not exposed to weather or in contact with ground: Slabs, walls, joists: 42 mm and 58 mm bars ............................................................... 40 mm 36 mm bars and smaller ................................................................ 20 mm Beams, columns: Primary reinforcement, ties, stirrups, spirals ................................. 40 mm Shells, folded plate members: 20 mm bar and larger .................................................................... 20 mm 16 mm bar, MW200 or MD200 wire, and smaller ........................ 12 mm 407.8 Concrete Protection for Reinforcement 407.8.2 Precast Concrete (Manufactured Under Plant Control Conditions) Unless a greater cover is required by Section 407.8.6 or 407.8.8, specified cover for prestressed and nonprestressed reinforcement, ducts, and end fittings shall not less than the following: Minimum Cover 1. a) Concrete exposed to earth or weather: Wall panels: 42 mm and 58 mm bars ............................................................................. 40 mm 36 bar and smaller, prestressing tendons larger than 40 mm and smaller, MW200 or MD200 wire and smaller ....................................... 20 mm Other members: 42 and 58 mm bars, prestressing tendons larger than 40 mm .................. 50 mm 20 mm through 36 mm bars, prestressing tendons larger than 16 mm through 40 mm ................................................................ 40 mm 16 mm bars and smaller, prestressing tendons 16 mm diameter and smaller, MW200 or MD200 wire, and smaller ...................................... 30 mm b) 407.8 Concrete Protection for Reinforcement 2) a) Minimum Cover Concrete not exposed to weather or in contact with ground: Slabs, walls, joists: 42 mm and 58 mm bars, prestressing tendons larger than 40 mm ............................. 30 mm Prestressing tendons 40 mm and smaller ........................... 20 mm 36 mm bar and smaller, MW200 or MD200 wire and smaller ................................... 15 mm Beams, columns: Primary reinforcement db but not less than 15 mm and need not exceed ......................... 40 mm Ties, stirrups, spirals ............................................................. 10 mm Shells, folded plate members: Prestressing tendons ............................................................ 20 mm 20 mm bar and larger ......................................................... 15 mm 16 mm bar, MW200 or MD200 wire and smaller ............. 10 mm b) c) 407.8 Concrete Protection for Reinforcement 407.8.3 Cast-In-Place Concrete (Prestressed) 407.8.3.1 Unless a greater cover is required by Sections 407.8.6 and 407.8.8, specified cover for prestressed and nonprestressed reinforcement, ducts and end fittings, shall not less than the following: Minimum Cover Concrete cast against and permanently exposed to earth .............................. 75 mm Concrete exposed to earth or weather: Wall panels, slabs, joists ................................................................................. 25 mm Other members .............................................................................................. 40 mm Concrete not exposed to weather or in contact with ground: Slabs, walls, joists ........................................................................................... 20 mm Beams, columns Primary reinforcement ................................................................................... 40 mm Ties, stirrups, spirals ...................................................................................... 25 mm Shells, folded plate members: 16 mm bars, MW200 or MD200 wire, and smaller ..................................... 10 mm Other reinforcement ............................................................................... db > 20 mm 1. 2. 3. a) b) c) 407.8 Concrete Protection for Reinforcement 407.8.3.2 For prestressed concrete members exposed to earth, weather or corrosive environments, and in which permissible tensile stress of Section 418.5.1, Item 3, is exceeded, minimum cover shall be increased 50 percent. 407.8.3.3 For prestressed concrete members manufactured under plant control conditions, minimum concrete cover for nonprestressed reinforcement shall be as required in Section 407.8.2. 407.8.4 Bundled Bars For bundled bars, minimum concrete cover shall not be less than the equivalent diameter of the bundle, but need not be greater than 50 mm; except for concrete cast against and permanently exposed to earth, minimum cover shall not be less than 75 mm. 407.8.5 Headed Shear Stud Reinforcement For headed shear stud reinforcement, specified concrete cover for the heads or base rails shall not be less than that required for the reinforcement in the type of member in which the headed shear stud reinforcement is placed. 407.8 Concrete Protection for Reinforcement 407.8.6 Corrosive Environments In corrosive environments or other severe exposure conditions, amount of concrete protection shall be suitably increased, and the pertinent requirements for concrete based on applicable exposure categories in Section 404 shall be met, denseness and nonporosity of protecting concrete shall be considered, or other protection shall be provided. 407.8.6.1 For prestressed concrete members exposed to corrosive environments or other severe exposure categories such as those defined in Section 404, and which are classified as Class T or C in Section 418.4.3, specified concrete cover shall not be less than 1.5 times the cover for prestressed reinforcement required by Section 407.8.2 and 407.8.3. This requirement shall be permitted to be waived if the precompressed tensile zone is not in tension under sustained loads. 407.8 Concrete Protection for Reinforcement 407.8.7 Future Extensions Exposed reinforcement, inserts and plates intended for bonding with future extensions shall be protected from corrosion. 407.8.8 Fire Protection If the National Building Code, of which the National Structural Code of the Philippines forms a part, requires a thickness of cover for fire protection greater than the minimum concrete cover specified in Sections 407.8.1 through 407.8.7, such greater thickness shall be specified. 407.9 Special Reinforcement Details for Columns 407.9.1 Offset Bars Offset bent longitudinal bars shall confirm to the following: 407.9.1.1 Slope of inclined portion of an offset bar with axis of column shall not exceed 1 in 6. 407.9.1.2 Portions of bar above and below an offset shall be parallel to axis of column. 407.9.1.3Horizontal support at offset bends shall be provided by lateral ties, spirals or parts of the floor construction. Horizontal support provided shall be designed to resist one and one-half times the horizontal component of the computed force in the inclined portion of an offset bar. Lateral ties or spirals, if used, shall be placed not more than 150 mm from points of bend. 407.9 Special Reinforcement Details for Columns 407.9.1.4 Offset bars shall be bent before placement in the forms. See Section 407.4. 407.9.1.5 Where a column face is offset 75 mm or greater, longitudinal bars shall not be offset bent. Separate dowels, lap spliced with the longitudinal bars adjacent to the offset column faces, shall be provided. Lap splices shall conform to Section 412.18. 407.9 Special Reinforcement Details for Columns 407.9.2 Steel Cores Long transfer in structural steel cores of composite compression members shall be provided by the following: 407.9.2.1 Ends of structural steel cores shall be accurately finished to bear at end-bearing splices, with positive provision for alignment of one core above the other in concentric contact. 407.9.2.2 at end-bearing splices, bearing shall be considered effective to transfer not more than 50 percent of the total compressive stress in the steel core. 407.9.2.3 Transfer of stress between column base and footing shall be designed in accordance with Section 415.9. 407.9.2.4 Base of structural steel section shall be designed to transfer the total load from the entire composite member to the footing; or, the base may be designed to transfer the load from the steel core only, provided ample concrete section is available for transfer of the portion of the total load carried by the reinforced concrete section to the footing by compression in the concrete and by reinforcement. The End
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Report "National Structural Code of the Philippines"