FOUNDATIONS 317 



The formula for finding the area of steel reinforcement 

 required is expressed as follows: 



A-J^L.. 



in which A is the sectional area of steel reinforcement, in 

 square inches, required for each linear foot of spread footings 

 along one side; W, the total load, in pounds, on a portion of 

 projection of footing 1 ft. in width; x, the projection of 

 footing, in inches; and /, the distance, in inches, from center 

 of action of steel reinforcement to top surface of concrete 

 footing. 



/\ 



x-s-o" J 



or I 



I 



I I I Pressure on Sot/ ' 4000 to /xvSfv*, 



FIG. 4 



The following formula is used to determine the compres- 

 sion created on the concrete due to bending stress: 



c-E*. 



4.59*2 



The value C is the compression, in pounds per square inch 

 of section, and the other values are the same as in the first 

 formula. 



In order to explain the application of the preceding 

 formulas, assume that the reinforced-concrete footing of a 

 column is required to sustain 900,000 lb., and that, as the 

 soil will safely support 4,000 lb. per sq. ft. of bearing area, 

 the footing will be 900,000^-4,000 = 225 sq. ft. To obtain 

 this area, the footing will have to be 15 ft. square, and the. 



