CORRUGATED BAR COMPANY, INC. 



(assuming the use of deformed bars), the number of bars selected for moment consider- 

 ations may not be sufficient to accompUsh this. In this case the unit bond stress, 



(i°8±^)(2.71)(5,600) 



(14) (1.965) 5 



©^33) 



= 130 lb. per sq. in. 



The allowable bond stress is exceeded and it will be necessary, therefore, to increase 

 the number of ^" round bars required for moment in the ratio 130/100; or a total 

 of 18-^" round bars will be needed in each direction at a uniform spacing of 6 inches. 

 The quantities of material required by this design are: Concrete 233 cu. ft., steel 

 36-^" round bars 9' 3" long. 



The combined spread footing is employed in those cases where the footings under 

 wall columns are not permitted to extend beyond the building line; this necessitates 

 extending the footing under the wall column to the adjacent interior column and mak- 

 ing it of such dimensions that its center of area coincides with the center of gravity 

 of the column loads that bear upon it. The footing thus becomes a distributing beam, 

 uniformly loaded by the upward reaction of the soil, and is reinforced accordingly 

 in the upper face longitudinally between columns, and in the lower face transversely 

 under each column. 



The designs given in the tables on pages 136 to 139 cover a fairly wide range of con- 

 ditions and as will be noted it is only required to know the loads and the distance 

 center to center of the columns to obtain a complete solution of the problem. Results 

 are all given in terms of the distance / in feet center to center of columns. Where con- 

 ditions depart from what might be called the average, the results given in the tables 

 will be slightly in error but not sufficiently so to disturb the safety or economy of the 

 design. 



Example — Given a 24-inch square wall column carrying a load Pi, of 350,000 

 pounds and a 26-inch diameter interior column carrying a load P-2, of 450,000 pounds, 



or /p =1.3. The columns are spaced 18 feet on centers and the allowable soil 



pressure is 6,000 pounds per square foot. 



The sum of the loads is 800,000 pounds and the distance c is one foot. Entering 



the table on page 138 with Pi+P2 = 800,000 we find opposite the ratio ^V^ =1.3; 

 the following dimensions and steel areas: 



L =1.13/-f2c=(1.13)(18)-F(2)(l)=22.34ft. 



H =0.2/+0.25 = (0.2)(18)-|-(0.25) = 3.85ft. 

 h =3.6-^=3.6-^=0. 60ft. 



D O 



^9 =27.3 sq. in. 



., 2,465 2.465 _ ^ . 

 As=-ir- =(i8yi =7.60 sq.m. 



,„ 1,895 1,895 ^ ^^ 

 A 8= -^ =^Yg^= 5.85 sq.m. 



134 



