Beams With Horizontal Bars Only

Par. 64. - For beams with horizontal bars only and without web reinforcement, two per cent.

Beams With Web Reinforcement

Par. 65. - For beams with web reinforcement consisting of vertical stirrups looped about the longitudinal reinforcing bars in the tension side of the beam, suitably anchored in the compression side and spaced horizontally not more than one half the depth of the beam, or for beams in which longitudinal bars are bent up at an angle of not more than forty-five degrees nor less than twenty degrees with the axis of the beam and the points of bending are spaced horizontally not more than three fourths of the depth of the beam apart, or both, the web reinforcement being designed, in each case, to carry two thirds of the total shear, six per cent.

Par. 66. - Punching. - Punching shear shall not exceed six per cent of the compressive strength fixed by this act.

Par. 67. - Bond. - The bond stress between concrete and steel bars shall not exceed four per cent, except that the bond between concrete and approved deformed steel bars shall not exceed five per cent, and between concrete and drawn wire shall not exceed three per cent of the compressive strength fixed by this act.

Par. 6S. - Steel. - The tensile or compressive stress in steel shall not exceed sixteen thousand pounds per square inch in rods and twenty thousand pounds per square inch in drawn wire and other approved cold stretched fabric, except that in slabs of stone concrete the tensile stress in rods shall not exceed eighteen thousand pounds per square inch, and in drawn wire and other approved cold stretched fabric it shall not exceed twenty-two thousand five hundred pounds per square inch.

Par. 69. - Modulus of Elasticity. - The modulus of elasticity of concrete shall be taken as -

1/30 that of steel for cinder concrete with a compressive strength of 1,000 pounds per square inch or less.

1/15 that of steel for stone concrete with a compressive strength of 2,200 pounds per square inch or less.

1/12 that of steel for concrete with a compressive strength greater than 2,200 pounds per square inch, but less than 2,900 pounds per square inch.

1/10 that of steel for concrete with a compressive strength of 2,900 pounds per square inch or more, the compressive strength referred to in all these cases being that fixed by this act.

Par. 70. - Footing General. - Symmetrical, concentric column footings shall be designed for punching shear, diagonal tension and bending moment.

Par. 71. - Punching Shear in Footings. - The area effective to resist punching shear in column footings shall be considered as the area having a width equal to the perimeter of the column or pier and a depth equal to seven-eighths the depth of footing from top to centre of reinforcing steel.

Par. 72. - Diagonal Tension in Footings. - Shearing stresses as indicative of diagonal tension shall be measured in footings on vertical sections distant from the face of the pier or column equal to the depth of the footing from top to centre of reinforcing steel.

Par. 73. - Bending Moment in Footings. - The bending moment in rectangular isolated column footings at a section taken at the edge of pier or columns shall be determined by multiplying the load on the cantilever projection by three eighths the distance from the edge of pier or column to the edge of footing. The section of maximum moment in a footing supporting a round column or pier shall be taken one eighth the radius from the tangent toward the centre. The effective area of concrete and steel to resist bending moment shall be considered as that within a width extending both sides of pier or column a distance equal to depth of footing plus one half the remaining distance to edge of footing, except that reinforcing steel crossing the section other than at right angles shall be considered to have an effective area determined by multiplying the sectional area by the sine of the angle between the bar and the plane of the section. The bond stress in the steel shall not exceed that allowed by this act.

Par. 74. - Flat Slabs. - Floor slabs supported upon columns without beams or girders and extending two or more bays in each direction shall conform to the following requirements.

Par. 75. - Capital. - Columns may be provided with enlarged capitals. The horizontal width of capitals shall be taken where the vertical thickness is at least one and one half inches, and the contour of capitals shall not fall within that of an inverted cone or pyramid whose apex is on the centre line of the column, whose sides incline at forty-five degrees with the vertical, and whose base lies in a plane one and one half inches below the underside of the dropped panel and, if no dropped panel is used, below the underside of the slab, and has the same size and shape in plan as the capital. The width of capital in any direction shall not be less than one fifth the distance, centre to centre, of columns in that direction, and shall be such that the allowable unit stresses elsewhere specified in this act shall not be exceeded.

Par. 76. - Dropped Panel. - A thickening of the slab on the underside in the vicinity of the columns is termed a dropped panel. The width of the dropped panel in any direction shall be not less than 3/2 that of the column capital. The depth of the dropped panel below the bottom of the slab shall be not more than half the slab thickness, but shall be such that the allowable unit stresses shall not be exceeded either in shear about the column capital or in bending. The allowable unit shear to be used shall be that specified for punching shear elsewhere in this act. The allowable compression in bending shall be that specified for extreme fibers adjacent to support in continuous beams.

Par. 77. - Slab Thickness. - In flat slab construction, the minimum thickness of slab shall be not less than 1/40 in the case of roofs or 1/32 in the case of floors, of the distance from centre to centre of the columns in the longer direction. The thickness shall be such as to withstand the shear about the column capital or dropped panel without exceeding the allowable stress herein specified for punching shear.