STATE GEOLOGIST. 141 
tions was designed. These foundations consisted of beds of concrete with 
grillages of steel rails or I-beams bedded in concrete, on top of them. 
Such foundations have long been successfully used there under the most 
trying conditions. : 
Fig. 77.—A Flat Elliptical Arch Bridge. 
In order to compare the two forms, figures 78 and 79 are taken from 
an article by Mr. T. Corydon Purdy, published in Engineering News. 
Both foundations begin with a bed of concrete 18 inches thick and 16% 
feet square. Both were designed to carry a load of 800,000 pounds. The 
height of the steel-concrete foundation is 18 inches over the base, while 
the stone foundation is 7 feet. The weight of the steel concrete founda- 
tion 1s 103,000 pounds, and that of the stone foundation is 261,000 pounds. 
The reduction in weight is more than sufficient to allow an additional 
story to the building without extending the footings. The decreased 
depth of footings allows space for a basement. The steel concrete founda- 
tion can be erected in much shorter time. It is susceptible of development 
into cantilever form and therefore becomes particularly useful for sus- 
taining separate walls along party lines. Thus steel concrete foundations 
save in basement space, in weight upon foundation soil, in tirne of con- 
struction, and in first cost. 
The I-beam grillage, however, used a great deal of steel which it has 
since been discovered could be saved by using much smaller bars or rods 
imbedded in the concrete in grillage form. Figures 80 and 81 show an- 
other comparison which the St. Louis Expanded Metal Company make, 
and in which they claim that the first cost of construction saved by using 
bars is nearly as great as the saving in space. 
