56 

 If the neutral axis falls within the slab formulae and 



can be used by substituting the value ^ - 



3 



In place of 6 = 12 in. If the neutral axis passes through 

 the bottom of the slab, use bi instead of b. In most 

 cases the figured shear will exceed the safe shear on the 

 concrete (65 Ib. per sq. in.) 



If the cross-section of a side of a U is a, then the V 

 will resist a shear equal to 2.a. 10,000 Ib. 



Formula (c) gives the unit horizontal shear in the 

 concrete and generally exceeds the safe shearing stress of 

 65 Ib. per sq. in. By bending up some of the bars at a 

 distance from point of support some more of the shear 



( Vmax- V )Clear span 

 can be taken up. By using = - 



Total weight on the beam 

 the point of bending up the bars is determined. 



In bending up bars the adhesion of the remaining 

 straight bars in the bottom of the beam must be investi- 

 gated. Use formula (d) for this. 



In order to facilitate computations in estimating, the 

 following table has been prepared, which gives values of 

 K for various total loads per foot of beam and different 

 effective depths. The table is figured for twisted steel or 

 patented bars using 20,000 Ib. per sq. in. on the steel. 



Wl 



The moment used was 



assuming continuous action of the beams. For other 



as and values of fiber stress in steel use 

 Wl (total load in Ib. per ft.) (12') (Span in feet) 



IT" / effective depth \ / Working value of steel \ / . \ 

 \ in inches / \ in Ib. per sq. in. / \ ) 



whon x = 8; 9 or 10; ir/ = 7 <//2 Tables on pages 64, 05 and 

 60. 



To determine the compression, take the area of steel 

 roquiivil :unl multiply same by Uo.ooo Ib. or other fiber 

 stress. This gives the total compression. Multiply the 

 clear span divided by 3 (if this value does not exceed 

 the spacing of beams) by the thickness of your slab, or 

 distance to the neutral axis as it passes within the slab. 

 This gives the amount of compression the concrete will 

 take. If this is less than the total compression, provide 

 steel at 10,000 Ib. per sq. in. to take the remainder. 



