Par. 78. - Bending. - For the purpose of determining the bending in flat slab floors, the slab shall be considered as divided by lines parallel to the lines of columns into strips whose width is one half the distance, L, centre to centre, of columns measured at right angles to the span of strips. The centre line of alternate strips shall coincide with the centre line of the columns. These shall be known as A-strips. The other strips located midway between columns shall be known as B-strips. The span length of the strips shall be taken as the distance, centre to centre, of columns less two thirds the width of the column capital measured in the direction of the span.

A and B Strips Comprising Any Panel Width

Par. 79. - Provision shall be made in the A and B strips comprising any panel width for the whole bending moment specified, and the proportion of the whole provided for within each strip shall be not less than that given in the following table: -

Par. 80. - Interior Bays. - If l = span as given above - L - 2/3 c where c = diameter of column capital w = total load per square foot whether the panels be square or oblong and in whichever direction the span be taken, the bending moments at the critical portions of interior bays shall be assumed as follows: -

Par. 81. - Positive Bending. - The positive bending moment for a whole panel width shall be taken as

M=wLl2/25

Par. 82. - Negative Bending. - The negative bending moment for a panel width shall be taken as

M=wLl2/15

Par. 83. - Wall Bays; Restraint. - For wall bays when the wall is of reinforced concrete (l is the distance from the inside face of the exterior column to the centre of the interior column less one third the width of the interior column capital) the bending moment for strips running perpendicular to the wall shall be as follows: -

Par. 84. - Positive Bending. - The positive bending moment for a panel width shall be taken as

M=wLl2/20 Par. 85. - Negative Bending. - The negative bending moment for a panel width at the interior line of columns shall be taken as: -

M=wLl2/12.5 Par. 86. - The negative bending moment for a panel at the wall shall in general be taken as: -

M=wLl2/30 Par. 87. - This may be increased, according to degree of restraint, up to wLl2/15 for complete restraint: provided, however, that in case the coefficient for negative bending at the wall is increased, the other two bending moment coefficients may be correspondingly decreased.

Par. 88. - Wall Bays; No Restraint. - For wall bays supported on one edge upon brick walls or other construction incapable of providing adequate restraint in negative bending, I is the distance from the inner face of the wall to the centre of the interior column less one third the width of the interior column capital.

Par. 89. - Positive Bending. - The positive bending moment for a panel width shall be taken as: -

M=wLL2/16 Par. 90. - Negative Bending. - The negative bending moment for a panel width at the interior column line shall be taken as: -

M=wLl2/10

Par. 91. - Negative bending along such walls shall be provided for by reinforcement in the top of the slab at right angles with the wall equal to four tenths per cent in floors and to two tenths per cent in roofs of the area of cross-section of the slab.

Par. 92. - Bays discontinuous upon one or two adjacent sides shall be treated as wall bays.

Par. 93. - When a flat slab is supported by a beam or wall on one or two sides, the half strip parallel with and adjacent to the beam or wall may be reinforced as half a B-strip.

Par. 94. - The bending in exterior concrete columns supporting flat slab floors shall in general be taken as: -

wLl2/30 plus Wh/4' or more up to wLl2/15 plus Wh/4 in case of complete restraint, where W is the total load on the wall panel and h is the thickness of the exterior column.

Par. 95. - For floors, half this bending shall be assumed as acting below and half above the slab; for roofs the whole bending acts below the slab.

Par. 96. - Brackets. - Brackets or haunches shall be provided on exterior columns when necessary to transmit the shear and bending from the slab to the column.

Par. 97. - Interior Columns. - The least dimension of interior concrete columns supporting flat slabs shall be not less than one fifteenth the span, centre to centre, of columns in the longer direction.

Par. 98. - Reinforcement. - Reinforcement shall be provided at the critical sections of all strips in sufficient quantity to withstand the bending herein specified without exceeding the allowable unit stresses elsewhere specified in this act. Reinforcement lying obliquely to the axis of any strip shall be counted as having an area effective for that strip equal to its actual area of cross-section multiplied by the cosine of the angle which it makes with the axis of the strip.

Par. 99. - Bent Bars. - No reinforcing for positive bending shall be bent up to the top of the slab further from the centre line of the column than one fourth L where L is the distance, centre to centre of columns in the direction of the reinforcing. Positive reinforcement in A-strips shall be provided to within 0.15 L of the centre line of interior columns and extending to the inside face of wall columns; in B-strips shall be provided extending to within 0.10 L of the interior column line and to the inside face of wall support. Negative reinforcement in A-strips shall extend beyond the centre line of the columns half the width of the column capital plus enough to develop the strength of the rods; at least one quarter of the negative reinforcement shall extend six inches beyond the quarter point of the panel or the fifth point of the span length. Negative reinforcement in B-strips shall extend forty diameters beyond the centre line of columns, and at least half thereof shall extend to the quarter point of the panel.