Bridge Specifications (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1908 Excerpt: ... D. In the present case, the smallest-sized roller (3 inches, B. S., Art. 153) gives sufficient resistance to transmit the reaction, as will be shown presently. It is customary to space the rollers about i inch apart for the full length of the pedestal. In the present case, if the end rollers /, / are each placed i inch from the end of the plate /, there is just room for nine rollers in the length of the pedestal. The rollers are usually made at least as long as the distance between the outside edges of the base angles g, in this case about 23 inches. Nine rollers at 23 inches gives 207 linear inches of rollers, which, at 600 X 3 = 1,800 pounds per linear inch, can support 372,600 pounds. As this is greater than the reaction, these rollers (that is, nine rollers 23 inches long) are sufficient. If the allowable load had been less than the reaction, it would have been necessary to use either longer rollers or rollers of larger diameter. The rollers are fastened together so as to form what is known as a roller nest, in the manner shown in Fig. 27 (d). Short bolts m, m, known as studs, about f inch in diameter, are set into the ends of each roller about li inches, and the ends left to project a inch at each end. A flat bar n is placed on each end of the rollers, and the short bolts fit into holes in this bar. The bars n are kept in position by the bolts 0 and additional bars p at each end of the nest; the bars p are i inch longer than the rollers, and are inserted between the ends of the side bars n. A plate about 2 inches in thickness is inserted under the rollers to give them a smooth surface to roll on, and also to distribute the pressure more evenly over the masonry. The bearing surfaces above and below the rollers are provided with projections q that fit i...