20 



tion rollers or rockers running between planed surfaces. 

 These rollers shall not be less than 4} inches diameter for 

 spans 100 feet or less, and for greater spans this minimum 

 diameter shall be increased in proportion of i inch for each 

 loo feet additional. 



The rollers shall be so proportioned that the pressure 

 per lineal inch of roller shall not exceed the product of the 

 diameter in inches by 300 pounds (3Ood.). 



The rollers must be of machinery steel and the bearing 

 plates of medium steel. 



The rollers and bearings must be so arranged that they 

 can be readily drained and cleaned. 



115. Bridges less than 80 feet span shall be secured at 

 one end to the masonry, and the other end shall be free to 

 move longitudinally upon smooth surfaces. 



1 16. Where two spans rest upon the same masonry, a con- 

 tinuous plate, not less than | inch thick, shall extend under 

 the two adjacent bearings, or the two bearings must be 

 rigidly tied together. 



Pedestals and 117. Pedestals shall be made of riveted plates and angles. 

 All bearing surfaces of the base plates and vertical webs 

 must be planed. The vertical webs must be secured to the 

 base by angles having two rows of rivets in the vertical 

 legs. No base plate or web connecting angle shall be less 

 in thickness than f inch. The vertical webs shall be of 

 sufficient height and must contain material and rivets 

 enough to practically distribute the loads over the bearings 

 or rollers. 



Where the size of the pedestal permits, the vertical webs 

 must be rigidly connected transversely. 



1 1 8. All the bed-plates and bearings under fixed and 

 movable ends must be fox-bolted to the masonry ; for 

 trusses, these bolts must not be less than i inches diameter ; 

 for plate and other girders, not less than -J inch diameter ; 

 and must be inserted at least six diameters into the masonry. 

 The contractor must furnish all bolts, drill all holes and set 

 bolts to place with sulphur or Portland cement. 



119. While the expansion ends of all trusses must be free 



