76 CAMBKIA STEEL. 



SPACING OF TIE RODS FOR TILE ARCHES. 



The table on the next page was computed from the following 

 formula, which was obtained from that giving the thrust of 

 arches on page 75. 



AxRX 10000 

 WL* 



in which 



B = spacing of tie rods in feet. 



A = net area of rod in square inches. 



R = rise of arch in inches. 



W = load in pounds per square foot of the arch. 



L = span of arch in feet. 



The above formula gives the spacing of tie rods corresponding 

 to a tensile stress in the rods of 15 000 pounds per square inch, 

 without considering the flexure of the beams. 



In spacing tie rods, the lateral strength of beams, for flexure due 

 to the thrust of the arches, should be taken into consideration, 

 explanations for which are given on pages 78 to 81 inclusive. 



Spacings for other loads than that of the table may be found 

 by proportion, thus: 



Required spacing = 



100 + weight of arch in pounds per square foot 

 New load in Ibs. per sq. ft. + weight of arch in Ibs. per sq. ft. X 8 P acm S fro 



Weights of tile arches per square foot are given on page 69. 



As noted under the heading "Lateral Strength of Beams," on 

 pages 82 and 83,care should be taken that the spacing of tie rods 

 is not greater than twenty times the least flange width, otherwise 

 the safe loads should be reduced to compensate for the strains 

 produced by flexure of the upper flange considered as a column 

 in compression. 



