36 STANDARD SPECIFICATIONS 



of i inch for each 10 ft. in length. Efficient means shall be 

 provided to prevent excessive motion at any one point. 



For bridges less than 80 ft. in length one end shall be free to 

 move upon smooth surfaces. 



Bridges of 80 ft. and over, resting on masonry, shall have 

 hinged bolsters or shoes at both ends. At one end the shoes 

 shall rest upon a nest of turned expansion rollers, or rockers may 

 be used for the same purpose. 



Expansion rollers shall not be less than 4 in. in diameter. 

 (Par. 117e.) They shall be coupled together with substantial side 

 bars which shall be so arranged that the rollers can be readily 

 cleaned. (Par. 133.) 



k- 1 In very high trestle towers one foot shall be fixed, two feet 

 shall be fixed in one direction only, and the fourth shall be free 

 to move in both directions. 



