292 



FLOORS 



should have a thickness of from 2 to 4 inches of concrete over the cen- 

 ter of the arch. Beams are spaced from 4 to 7 feet apart for this floor, 

 and tie rods are used as in the brick arch floor. 



Expanded Metal Floors. The floor shown in Fig. 142 is con- 

 structed as follows : A wood centering is suspended from the beams, 

 with the upper surface of the centering about I inch below the top of 

 the beams, a layer of expanded metal is stretched across the beam 

 in sheets and the concrete is spread over and tamped so that the ex- 

 panded metal becomes imbedded in the lower inch of the concrete. The 



FIG. 142. 



concrete is usually made of I part Portland cement, 2 parts sand and 

 6 parts cinders, and weighs 80 to 90 pounds per cubic foot. Beams 

 were formerly spaced from 5 to 8 feet apart, but have recently been 

 spaced much farther; spacings as wide as 18 to 20 feet having been 

 successfully employed. Expanded metal with 3-inch mesh cut from No. 

 10 gage sheet steel is commonly used for floors, which are made 

 from 3 to 5 or 6 inches thick. There is at present no rational method 

 for the design of expanded metal floors descriptions of floors in actual 

 use, and tests of floors may be found by consulting the volumes of the 

 Engineering News, the Engineering Record, and other technical papers. 

 The companies controlling the patents will erect floors for specified 

 loads under a guarantee. 



Expanded metal floors are also made as shown in Fig. 143. This 

 type is adapted to very heavy floor loads. The arch should have a rise 



FIG. 143. 



