FOUNDATIONS. 



75 



, 



LOADS. ON FOUNDATIONS. Schneider's specifications require that: 



"The live loads on columns shall be assumed to be the same as for the footings of columns. 

 The areas of the bases of the columns shall be proportioned for the dead load only. That founda- 

 tion which receives the largest ratio of live to dead load shall be selected and proportioned for the 

 combined dead and live loads. The dead load on this foundation shall be divided by the area 

 thus found and this reduced pressure per square foot shall be the permissible working pressure to 

 be used for the dead load for all foundations." 



PRESSURE ON FOUNDATIONS. The following allowable pressures may be used in 

 the absence of definite data. No important structure should be built without the making of 

 careful tests of the bearing power of the soil upon which it is to rest. 



The loads on foundations should not exceed the following in tons per square foot: 



Ordinary clay and dry sand mixed with clay 2 



Dry sand and dry clay . , 3 



Hard clay and firm, coarse sand 4 



Firm, coarse sand and gravel 5 



Shale rock 8 



Hard rock 20 



"or all soils inferior to the above, such as loam, etc., never more than one ton per square foot. 

 The Chicago Building Ordinance (1911) requires that: 



" (a) If the soil is a layer of pure clay at least fifteen feet thick, without admixture of any 

 foreign substance other than gravel it shall not be loaded to exceed 3,500 Ib. per sq. ft. If the 

 soil is a layer of pure clay at least fifteen feet thick and is dry and thoroughly compressed, it may be 

 loaded not to exceed 4,500 Ib. per sq. ft. 



" (b) If the soil is a layer of firm sand fifteen feet or more in thickness, and without admixture 

 of clay, loam or other foreign substance, it shall not be loaded to exceed 5,000 Ib. per sq. ft. 



" (c) If the soil is a mixture of clay and sand, it shall not be loaded to exceed 3,000 Ib. per 

 sq. ft. 



"Foundations shall in all cases extend at least four feet below the surface of the ground 

 upon which they are built, unless footings rest on bed rock." 



. PRESSURE ON MASONRY. The allowable stresses in masonry and pressures of beams, 

 girders, column bases, etc. on masonry as given in Table VIII represent good practice. 



TABLE VIII. 

 ALLOWABLE STRESSES IN MASONRY AND PRESSURES OF BEARING PLATES. 



BEARING POWER OF PILES. The maximum load carried by a pile should not exceed 

 40,000 Ib. Piles should be driven not less than 10 ft. in hard material, nor less than 20 ft. in soft 

 material if the pile is to be loaded to full bearing. The safe load should not exceed that given by 

 the Engineering News formula (i), Chapter XIV. 



THICKNESS OF WALLS. The minimum thickness of curtain walls in steel skeleton 

 buildings should be 12 in. for brick or concrete and 8 in. for reinforced concrete. 



