FIREPROOF FLOORS 



291 



Brick Arch Construction 



FIG. 140. 



layer of brick about 4 inches thick, with a span of 4 to 8 feet and a cen- 

 ter rise of preferably not less than y% the span. The space above the 

 brick arch is filled with concrete and a wearing floor is nailed to strips 

 imbedded in the surface of the concrete. The most desirable span is 

 from 4 to 6 feet. Tie rods are commonly placed at about y$ the height 

 of the beam and are spaced from 4 to 6 feet apart. The thrust of the 

 arch per lineal foot can be found by the formula 



1.5 W Z 2 



T = 



R 



where T = thrust of arch in Ibs. per lineal foot; 



W = load on arch in Ibs. per square foot ; 



L. = span of the arch in feet ; 



R = rise of arch in inches. 



The weight of this floor is about 75 Ibs. per square foot. 

 Corrugated Iron Arch Floor. The corrugated iron arch shown 

 in Fig. 141 makes a very strong floor for shops and mills. The cor- 

 rugated iron acts as a center for the concrete filling above it, and in 

 connection with the concrete makes a composite arch. The corrugated 

 iron or steel is ordinarily the standard 2^2 -inch corrugations, and the 

 gages are Nos. 16, 18 or 20, depending upon the load and the length of 

 span. The rise of the arch should not be less than 1-12 the span and 



Corrugated Iron Arch 



FIG. 141. 



