144 STEEL HIGHWAY BRIDGES. CHAP. III. 



nut. Bolts shall not be used in place of rivets except by special permission. Heads and nuts shall 

 be hexagonal. 



79. Indirect Splices. Where splice plates are not in direct contact with the parts which 

 they connect, rivets shall be used on each side of the joint in excess of the number theoretically 

 required to the extent of one-third of the number for each intervening plate. 



80. Fillers. Rivets carrying stress and passing through fillers shall be increased 50 per cent 

 in number; and the excess rivets, when possible, shall be outside of the connected member. 



81. Expansion. Provision for expansion to the extent of | in. for each 10 ft. shall be made 

 for all bridge structures. Efficient means shall be provided to prevent excessive motion at any 

 one point (32). 



82. Expansion Bearings. Spans of 60 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. 



83. Fixed Bearings. Movable bearings shall be designed to permit motion in one direction 

 only. Fixed bearings shall be firmly anchored to the masonry (87). 



84. Rollers. Expansion rollers shall be not less than 3 in. in diameter for spans of 100 feet 

 and less, and shall be increased I in. for each 100 ft. additional. They shall be coupled together 

 with substantial side bars, which shall be so arranged that the rollers can be readily cleaned. 



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

 the entire bearing. 



86. Pedestals and Bed Plates. Built pedestals shall be made of 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 J in. 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. t 



Where the size of the pedestal permits, the vertical webs must be rigidly connected trans- 

 versely. 



87. 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 ij in. diameter; for plate and other girders, 

 not less than in. diameter. 



The details of cast iron or cast steel shoes shall be subject to the special approval of the en- 

 gineer. 



88. Wall Plates. Wall plates may be cast or built up; and shall be so designed as to distrib- 

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



89. 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 (i i). 



90. 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. 



91. Camber. Truss spans shall be given a camber by making the panel length of the top 

 chords, or their horizontal projections, longer than the corresponding panels of the bottom chord 

 in the proportion of YS in. in 10 ft. Plate girder spans need not be cambered. 



92. 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 parallel to the axis of the truss as 

 possible, the maximum inclination of any bar being limited to one inch in 16 ft. 



PART V. MATERIALS AND WORKMANSHIP. 



MATERIAL. 



93. Process of Manufacture. Steel shall be made by the open-hearth process and shall 

 comply with the standard specifications of the Am. Ry. Eng. Assoc. 



(Sections 94 to 117 inclusive cover the Am. Ry. Eng. Assoc. Specifications for steel, see 

 specifications for railroad bridges, Chapter IV.) 



118. Timber. The timber shall be strictly first-class spruce, white pine, Douglas fir, Southern 

 yellow pine, or white oak bridge timber; sawed true and out of wind, full size, free from wind 

 shakes, large or loose knots, decayed or sapwood, wormholes or other defects impairing its strength 

 or durability. 



WORKMANSHIP. 



119. General. All .parts forming a structure shall be built in accordance with approved 

 drawings. The workmanship and finish shall be equal to the best practice in modern bridge works. 



1 20. Straightening Material. Material shall be thoroughly straightened in the shop, by 

 methods that will not injure it, before being laid off or worked in any way. 



121. Finish. Shearing shall be neatly and accurately done and all portions of the work 

 exposed to view neatly finished. 



122. Size of Rivets. The size of rivets, called for on the plans, shall be understood to mean 

 the actual size of the cold rivet before heating. 



