Page:Final Report - The Columbia River Interstate Bridge.pdf/28

 rails required for the two—gauge, double-track, street car tracks rest immediately upon the roadway cross floor beams and are fastened to them by standard Carnegie steel tie clips. The rails are 7 ins. high, so that there remains a space of 2 ins. in depth above the top of the concrete slabs to the top of the rail for the 2 ins. bitulithic surfacing which forms the pavement. To afford a rail heading which could be removed, if necessary, for access to the rails, or to the bonding, without injury to the roadway slab, the space about 5 ins. wide, on each side of each rail, is filled with concrete to the top of the rails, a flangeway being provided by forming this concrete. A drainage intake with down-spout is placed at intervals of fifty feet along each curb.

Engr. News.

This arrangement of floor has the advantage of providing a concrete slab longitudinal in the direction of travel, with comparatively short spans, and of making the supporting steel beams of very simple shop work. Owing to the lateral stiffness of the floor as constructed, the lower laterals of the spans are somewhat lighter than they would be for an open deck bridge.

Two fixed ends and two expansion ends of the spans are placed adjacent so as to reduce the number of expansion joints to a minimum. The expansion joints are made of usual type checkered plates supported by and sliding upon metal supports. The corresponding expansion joints for the rails between the spans consists of manganese-steel castings placed beside the webs of the rails, for which one side of the rail heads is planed off.

The towers supporting the lift span are of simple construction, riveted throughout, so arranged that the front columns of the towers support all the loads of the lift span and counterweights. The rear columns are bracing members. The lift span