SLAB, BEAM, AND COLUMN TABLES 189 



spending weight of slab is 47 Ib. per square foot and the total load for the 

 slab to carry is thus 297 Ib. This depth of slab will be considered satis- 

 factory and is on the side of safety. 



The area of steel per foot of breadth may be taken directly from Table 6 

 and, for the depth of slab chosen above, a a =0.277 sq. in. From Table 4 

 we may use 3/8 round rods spaced 43/4 in. on centers, or 7/16-in. rods 

 spaced 61/2 in., or 1/2-in. rods spaced 81/2 in., etc. 



5. Design the center cross-section of a T-beam in a floor system ; the beam 

 is to have a span of 12 ft. and be fully continuous. Maximum shear (live 

 plus dead) is closely equal to 12,200 Ib. Maximum moment (live plus 

 dead) =356,300 in.-lb. Supported slab is 6 in. thick. 



The breadth of the flange is controlled by one-fourth the span, or 36 in. 

 Using approximate formula (b) of Art. 59, assuming a depth (d) of 16 in. 



M 356,300 



~ (/.)(<*- 1/2/) ~ (16,000) (13.0) ~ 

 and 1.71 



also, / 6.0 



arieio" - 37 



Referring to Table 9, Part 1, it is seen at once that this beam falls under 

 Case I; that is, the neutral axis is in the flange. For the above value of 

 p, Table 3 gives / =0.914. The corrected value of a s is 

 _ M 356,300 



~~ " 



and I- 53 -OOQ27 



From Table 3 the stress in the concrete is found to be 350 Ib. per square 

 inch. The beam as designed is thus satisfactory. 



6. The flange of a T-beam is 24 in. wide and 4 in. thick. The beam is to 

 sustain a bending moment of 480,000 in.-lb. What depth of beam and 

 amount of steel is necessary? 



Try d = 18 in. Approximately, jd =16 in. Then formula (8) or formula 

 (b), Art. 59, gives: 



M 480,000 



a '= 



s=ii=- 222 



Referring to Table 9, Part 2, 



for /> = 0.004 and ^ = 0.222 (/.-456 1 



forp = 0.006 and ^ = 0.222 



Thus, 



for p = 0.0043 and ^ = 0.222 



The corrected value of o a is 



480,000 



1.84 sq. in. 



(16.000) (0.910) (18) 



