SLABS, CROSS-BEAMS, AND GIRDERS 



155 



be placed in the lower row, five 1 1/4-in. rods above, and two 1 1/4-in. 

 rods in the third row. Taking moments of areas about the center of the 

 lowest row, the center of gravity of the group is found to be 



> 

 16 



above this row. Hence, the lower row should be placed about 48 1/2 in. 

 below the top of the beam, thus giving a total depth, including the protective 

 covering, of 51 in. 



Bond for one rod (1 3/8 in.) at the end is 



(1.3197X42.0) ' 



For plain round rods, the number which must extend to the end of the 

 beam is 



485 



Six will be run to the end namely, the entire lower row of 1 3/8-in. rods 

 and also the center 1 1/4-in. rod of the second row. 



Web reinforcemejit will be provided by means of bent rods and vertical 

 stirrups. In bending up the rods, the two uppermost rods will be bent 

 up nearest the center. Two rods will be bent up at a time since bending 



r- 





m 



<I8-V 



ITQ 



u 



Neutral / /& 

 plane 



/"?&& / pp 



7 7^~'7 r 7lD~ 



'-^x^v^// 1 



Jfc \ / / ' /^ ?-~7'C. 



FIG. 75. 



the rods singly greatly complicates the handling and prevents a symmetrical 

 arrangement. The bends, also, will all be made at 45 degrees and the bent 

 ends extended far enough to give ample strength of bond. 



Web reinforcement is unnecessary at a distance from support equal to 

 40 (40)(18)(42.0) 

 2 4400 



The total stress to be taken by the inclined rods (and vertical stirrups, 

 if necessary) is represented by triangle ABC, Fig. 75. BC represents two- 

 thirds of the horizontal shear at the support per 1 in. length of beam. 



2Fb_2(88,000) 

 ~3M~3 (42.0) ' 

 r= 



X ~~ 





