156 REINFORCED CONCRETE CONSTRUCTION 



Hence, total stress to be taken by the rods 



-^(r) =-^(110) -76,700 Ib. 



But the area of one rod multiplied by 16,000 gives its tensile value, or 

 tensile value of one rod =(1.2272) (16,000) = 19,620 Ib. 



TA 7f"M"l 



Thus, only ' =4 rods are required if they can be bent up at the 

 19,0^0 



proper points. Six rods, however, will be bent up as a trial. 



The rods may be bent up at two at a time in the following order: 



s 2 =or <-2|l- 



(Note. Areas are used in the three preceding equations instead of the 

 number of rods, since rods are of two different sizes. The location of 

 the neutral plane, by formula (2) of Art. 59, is kd = (0.38) (47) = 17.9 in. 

 below the top of the beam.) 



The length V should equal 50 diameters (from table, Art. 43) or 



(50) (1.25) =62.5 in. = 5.2 ft. 



Fig. 75 shows the construction necessary to locate the points where the 

 rods should be bent to provide for diagonal tension. It is evident that the 

 rods can be bent at the desired points, but notice that the spacing between 

 two bends of the bent rods is greater than 3/4 d. Computations given 

 above show that only 4 rods are required at the end of beam and the bending 

 up of 8 rods should be tried unless it is intended to reinforce with vertical 

 stirrups as well. 



In the design at hand, with only six rods bent, the spacing of the bent 

 rods can either be made not greater than 3/4rf and stirrups supplied to 

 take the diagonal tension which would remain unprovided for, or else the 

 rods may be left as in Fig. 75 and stirrups employed throughout the length 

 of the beam. Double-looped stirrups, as shown, are advantageous in a 

 large beam of this kind and, even when stirrups are not theoretically neces- 

 sary, it is good design to use them throughout since they support the tension 

 rods, bind together the web and flange, and add greatly to the security 

 of the construction. For the beam under discussion, the stirrups should 

 be spaced about 2 ft. apart at the center of span varying to about 12 in. 

 at the ends. 



If it be possible in the design of a T-beam of this kind, that the live 

 load may be applied to one flange rather than uniformly over the whole 

 top, it may be necessary to provide transverse reinforcement in the upper 

 side of the beam. Usually if the stirrups are extended transversely some 

 distance beyond the width of web, as shown in Fig. 75, ample security will 

 be given. The required area of this steel may be determined per foot of 

 length of beam by treating the flange on either side of the web as a canti- 



