36 BULLETIN" 1259, U. S. DEPARTMENT OF AGEICULTUEE. 
that water will not be retained and that the roller nests 
may be inspected and cleaned with the minimum diffi- 
culty. 
47. Rockers. Pin-bcaring expansion rockers shall be of cast steel or 
cast iron. 
in^^" ^^x^^lns^n Shding plates for the expansion bearings of spans of 70 
bearings.' feet and over shall be of Class A bronze, conforming to 
the requirements of Section 8, Division I. These plates 
shall be chamfered at the ends and shall be held securely 
in position, usually by being inset into the metal of the 
pedestals and sole plates. Provision shall be made against 
any accumulation of dirt which will obstruct their free 
movement. 
49- Pedestals Pedcstals and shoes shall be designed to secure rigidity 
and stabihty and to distribute the reaction luiiformly 
over the entire bearing area. Preferably, they shall be 
made of cast steel or structural steel. The bottom bear- 
ing widths shall not exceed the top bearing widths by 
more than twice the depth of pedestal, and, when involv- 
ing pin bearings, this depth shall be measured from the 
center of pin. 
Where built pedestals and shoes are used, the web 
plates and the angles connecting them to the base plates 
shall be not less than 3^ inch thick. If the size of the 
pedestal permits, the webs shall be rigidly connected 
transversely. 
50. Inclined For spaus ou an mclined grade and without pin or 
earmgs. hinged bearmgs, the sole plate shall be beveled so that 
the substructure bridge seats will be level. 
51. Anchor Trusscs, girdcrs, and I-beam spans shall be securely 
^°^*^' anchored to their substructures. Anchor bolts shall be 
roughened by being screw-threaded or swedged to seciu-e 
a satisfactory grip upon the material used to embed 
them in the holes. 
The following are the minimum requirements for each 
bearing : 
For I-beam spans the outer beams shall be anchored at each 
end with two bolts 1 inch in diameter, set 10 inches in the 
masonry. 
For girder and truss spans — 
50 feet in length or less, 2 bolts, 1-inch diameter, set 10 
inches in masonry. 
51 to 100 feet in length, 2 bolts, 134 -inch diameter, set 12 
inches in masonry. 
101 to 150 feet in length, 2 bolts, 13^-inch diameter, set 
15 inches in masonry. 
151 feet and over, 4 bolts 13^-inch diameter, set 18 inches 
in masonry. 
Anchor bolts subject to tension, as in the colunon bases 
of trestle bents and towers, shall be designed to engage 
a mass of masonry which will secure a resistance equal 
to one and one-half times the calculated uplift. 
