RAILROAD BRIDGES 33 



1J in. and 1| in. respectively. The maximum distance from 

 any edge shall be eight (8) times the thickness of the outside 

 plate ; but shall not exceed 5 in. 



141. Tension Members. In calculating the net area of ten- 

 sion members the area of rivet holes must be deducted, assum- 

 ing the diameter of the hole to be J- in. larger than the nominal 

 size of the rivet. 



The length of riveted tension members in horizontal or 

 inclined positions shall not exceed 200 times their radius of 

 gyration about the horizontal axis. The horizontal projection 

 of the unsupported portion of the member is to be considered 

 as the effective length. 



Pin-connected riveted tension members shall have a net 

 section through the pin hole 25 per cent in excess of that through 

 the body of the main member. The minimum net section back 

 of the pin hole, parallel to the axis of the member, shall not be 

 less than that through the body of the main member. 



142. Eye-bars. The eye-bars composing a member shall be 

 so arranged that adjacent bars shall not have their surfaces in 

 contact; they shall be, as nearly as possible, parallel to the cen- 

 tral plane of the truss, the maximum inclination of any bar 

 being limited to 1 inch in 16 ft. 



Adjustable eye-bars, when used as counters, shall have the 

 screw ends upset and shall be provided with turnbuckles, or with 

 sleeve nuts provided with holes drilled through two opposite faces. 



143. Compression Members. In compression members form- 

 ing chord segments as much as possible of the metal shall be 

 concentrated in the webs and flanges and the neutral axis shall 

 be as near as possible to the center of the web. 



In all compression members the minimum thickness of each 

 single web plate shall be one-thirty-second (^j) of the distance 

 between the inner lines of rivets connecting it to the flanges 

 and, when two or more plates form a compound web, the min- 

 imum thickness of each plate shall be ^ in. (Par. 139.) 



The minimum thickness of cover plates shall be one-fortieth 

 (^) of the distance between rivet lines. 



No compression member shall have a length exceeding 100 

 times its least radius of gyration, except those used for wind 

 and lateral bracing, which may have a maximum length of 120 

 times their least radius of gyration. 



