CONSOLIDATED STEEL CORPORATION 



169 



SPACING OF TIE RODS 



Tie rods are used in fireproof floors to resist the thrust of the floor arches 

 and to hold the steel beams in position laterally. Rods of %-inch diameter are 

 generally employed for this purpose. They should be placed as near as possible 

 in the line of thrust of the arch, usually 3 inches above the bottom of the 

 beams. 



The proper spacing of tie rods is determined by two considerations. The 

 stress on the net area of the rod produced by the thrust of the arch must not 

 exceed 15,000 pounds per square inch. Also the lateral stress produced in the 

 beams or channels by the thrust of the arches must not be excessive. 



The spacing required to satisfy the first of these requirements is found in 

 the following manner: 



Let t = thrust of arch, in pounds per lineal foot. 

 r = rise of arch, in inches. 



/ = distance between beams, or span of arch, in feet. 

 w = load per square foot, in pounds, 

 a = net area of tie rod, in square inches. 

 d = distance between tie rods, in feet. 



Then, 



-, (1); and d= 



10,000ar 

 wl 2 ' 



(2). 



The net areas, in square inches, of the usual sizes of tie rods are as follows : 

 Diameter of rod = ^g-inch %-inch J^-inch 1-inch 



Net area, 



0.20 



0.30 



0.42 



0.55 



For %-inch rods, the size generally used, and for a total load of 150 pounds 

 per square foot the spacing given by formula (2) becomes d = 20r -v- p. 



The effective rise of flat tile arches may be assumed as 2 inches less than the 

 depth of the arch. 



The maximum spacing, in feet, of %-inch tie rods for a total load of 150 

 pounds per square foot, producing a stress of 15,000 pounds per square inch in 

 net area of rods, is given in the following table: 



MAXIMUM SPACING, IN FEET, OF '%-INCH TIE RODS FOR 

 A TOTAL LOAD OF 150 POUNDS PER SQUARE FOOT 



