318 FOUNDATIONS 



design shown in Pig. 4 may be assumed in applying the 

 formula. 



In this figure, the projection of the footing, or the dis- 

 tance x, is 60 in., and the dimension t, or the distance from 

 the center of action of the steel reinforcement to the top 

 of the footing, is 20 in. The pressure on a projection of 

 the footing 1 ft. in width is equal to the unit pressure on the 

 soil, or, 4,000X5 = 20,000 lb., which is the value of W in the 

 formula. These values may be substituted in the formula 

 for determining the amount of the steel reinforcement, so that 



20,000 X 60 



A= = 2.2 sq. in. 



27,000X20 



This area of steel is to be included in each linear foot of 

 the footing course; therefore, the reinforcement may consist 

 of 1-in. square twisted bars spaced practically every 6 in. 

 both ways, or other bars at a spacing to give this sectional 

 area may be used. 



The amount of the steel reinforcement having thus been 

 determined, it remains to find out whether or not the con- 

 crete in the footing course is overstressed, and the second 

 formula may be applied as follows: 



This result, which is the maximum compression, in pounds 

 per square inch, on the concrete section, is somewhat high. 

 If good concrete is used, the footing as reinforced and 

 designed may be considered safe, though, in fact, the thick- 

 ness of the concrete footing might be increased several 

 inches. _ 



CANTILEVER FOUNDATIONS 



In reinforced -concrete construction, as well as in other 

 types of construction, it is frequently necessary to place a 

 new building close against the walls of an adjoining building. 

 In many instances the wall of the adjoining property rests 

 entirely on its own lot and is not a party wall built half on 

 each side of the party line; also, the adjoining building may 

 be of inferior construction or may be occupied by tenants 



