190 REINFORCED CONCRETE CONSTRUCTION 



Another and perhaps better method of arriving at the same results is as 

 follows: 



M 480,000 

 = ~- 



For this value of r -j* and for ^ = 0.222, Table 9, Part 2, shows p to have a 

 bd 2 a 



value between 0.004 and 0.006. 



86.9 61.6 ~ 9 



58.4 58.4 p = 0.004 + =|j| (0.002) = 0.0042 



28.5 3.2 



O O 



/ c =,456 +-|^(163) =475 Ib. per square inch. 

 2o>o 



a 8 = (24)(18)(0.0042)=1.82 sq. in. 



Suppose that the flange of the above beam had been made 5 in. thick and 

 that the depth (d) had been taken at 16 1/2 in. 

 Then, 



?= 



Referring to Table 9, Part 2, 



Thus, 



for p = 0.0043 and -. = 0.30 . . I / ~ '? 



d ( Jc = 457 



for p = 0.0060 and ^ = 0.30. . . ( / = 



d { Jc = 565 



f or p = 0.0054 and ' =0.30 



d ( Jc= 527 



= 2.04 sq. in. 



The corrected value of a a is 



480.000 

 (16, 000) (0.893) (16. 5) 



7. Design a T-beam with span of 40 ft. Assume dead load = 1400 Ib. 

 per foot. Live load =3000 Ib. per foot. The beam is to be simply sup- 

 ported at the ends and the flange is to be proportioned as well as the web; 

 that is, the flange does not form a part of a floor system already determined. 



From Art. 61, 6' =18 in. and d =47 in. are suitable dimensions and a 

 thickness of flange of 12 in. is tried. The total bending moment on the beam 

 is 10,560,000 in.-lb. 



From Table 10. 



^ = 0.414 2=4.97 /d = 42.0 



From Formula (7), Art. 59. 



10,560,000 

 * (16, 000) (42.0) 

 The detailed design of this beam has been given at the end of Art. 61. 



