212 STEEL RAILWAY BRIDGES. CHAP. IV. 



60. Expansion Bearings. Spans of 80 ft. and over resting on masonry shall have turned 

 rollers or rockers at one end; and those of less length shall be arranged to slide on smooth surfaces. 

 These expansion bearings shall be designed to permit motion in one direction only. 



61. Fixed Bearings. Fixed bearings shall be firmly anchored to the masonry. 



62. Rollers. Expansion rollers shall be not less than 6 in. in diameter. They shall be 

 coupled together with substantial side bars, which shall be so arranged that the rollers can be 

 readily cleaned. Segmental rollers shall be geared to the upper and lower plates. 



63. Bolsters. Bolsters or shoes shall be so constructed that the load will be distributed over 

 the entire bearing. Spans of 80 ft. or over shall have hinged bolsters at each end. 



64. Wall Plates. Wall plates may be cast or built up; and shall be so designed as to distribute 

 the load uniformly over the entire bearing. They shall be secured against displacement. 



65. Anchorage. Anchor bolts for viaduct towers and similar structures shall be long enough 

 to engage a mass of masonry the weight of which is at least one and one-half times the uplift. 



66. Inclined Bearings. Bridges on an inclined grade without pin shoes shall have the sole 

 plates beveled so that the masonry and expansion surfaces may be level. 



FLOOR SYSTEMS. 



67. Floorbeams. Floorbeams shall preferably be square to the trusses or girders. They 

 shall be riveted directly to the girders or trusses or may be placed on top of deck bridges. 



68. Stringers. Stringers shall preferably be riveted to the webs of all intermediate floorbeams 

 by means of connection angles not less than 5-in. in thickness. Shelf angles or other supports 

 provided to support the stringer during erection shall not be considered as carrying any of the 

 reaction. 



69. Stringer Frames. Where end floorbeams cannot be used, stringers resting on masonry 

 shall have cross frames near their ends. These frames shall be riveted to girders or truss shoes 

 where practicable. 



BRACING. 



70. Rigid Bracing. Lateral, longitudinal and transverse bracing in all structures shall be 

 composed of rigid members. 



71. Portals. Through truss spans shall have riveted portal braces rigidly connected to the 

 end posts and top chords. They shall be as deep as the clearance will allow. 



72. Transverse Bracing. Intermediate transverse frames shall be used at each panel of 

 through spans having vertical truss members where the clearance will permit. 



73. End Bracing. Deck spans shall have transverse bracing at each end proportioned to 

 carry the lateral load to the support. 



74. Laterals. The minimum sized angle to be used in lateral bracing shall be 3! by 3 by f-in. 

 Not less than three rivets through the end of the angles shall be used at the connection. 



75. Lateral bracing shall be far enough below the flange to clear the ties. 



76. Tower Struts. The struts at the foot of viaduct towers shall be strong enough to slide 

 the movable shoes when the track is unloaded. 



PLATE GIRDERS. 



77. Camber. If desired, plate girder spans over 50 ft. in length shall be built with camber at 

 a rate of rV m - P er IO ft. f length. 



78. Top Flange Cover. Where flange plates are used, one cover plate of top flange shall 

 extend the whole length of the girder. 



79. Web Stiffeners. There shall be web stiffeners, generally in pairs, over bearings, at points 

 of concentrated loading, and at other points where the thickness of the web is less than -^ of the 

 unsupported distance between flange angles. The distance between stiffeners shall not exceed 

 that given by the following formula, with a maximum limit of six feet (and not greater than the 

 clear depth of the web) : 



d = (12,000 s), 

 40 



Where d = clear distance, between stiffeners of flange angles. 

 t = thickness of web. 

 5 = shear per sq. in. 



The stiffeners at ends and at points of concentrated loads shall be proportioned by the formula 

 of paragraph 16, the effective length being assumed as one-half the depth of girders. End stiffeners 

 and those under concentrated loads shall be on fillers and have their outstanding legs as wide as 

 the flange angles will allow and shall fit tightly against them. Intermediate stiffeners may be 



