Canadian engineer . on the outside of the truss, but these rivets, up tothe level of the tops of the girders, should be driven at the sametime that the riveting on the opposite side of the truss is done. In the development of this type of shallow floor fordouble track bridges, the first efforts were directed towardobtaining an open floor design, with stringers beneath thetrack, transmitting the load directly to the floor beam. Theexcessive bending moment in the floor beam, resulting fromthis arrangement, made it impracticable to design a floorbeam that would come within the required limits of
Canadian engineer . on the outside of the truss, but these rivets, up tothe level of the tops of the girders, should be driven at the sametime that the riveting on the opposite side of the truss is done. In the development of this type of shallow floor fordouble track bridges, the first efforts were directed towardobtaining an open floor design, with stringers beneath thetrack, transmitting the load directly to the floor beam. Theexcessive bending moment in the floor beam, resulting fromthis arrangement, made it impracticable to design a floorbeam that would come within the required limits of depth ffloor. Following this, a trough floor type was designed, difle--ing from the one shown on Fig. i in that it had no longi-tudinal girders to carry the troughs. Instead, the troughswere extended to the trusses and connected to the bottomchord in the same manner that the floor beam in Fig. i isconnected to the chord at the panel point. The bottom chordwas designed to act as a girder, to carry the panel loads to. rig. 2.—General Details of Shallour Open Bridge Floor. The deflection of this floor under a maximum load is con-siderably greater than that of floors designed for depths de-termined by economical sections. Under maximum load thetheoretical deflection at the centre of the floor beam is The erection of truss bridges of the open trough floortype requires a special order of work in riveting, owing tothe longitudinal girders being located so close to the the girders have been placed in position, no rivetingcan be done on the inside of the lower chord opposite thegirder. On this account all riveting in the trusses below thelevel of the tops of the girders must be done before the gir-ders go into place, which means that all lower chord splices,floor beam connections to trusses, and web member connec-tions to gusset plates, up to the level of the tops of thegirders, must be riveted before placing girders and trough the panel points. This design broug
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