Load Distribution of Diaphragms in I-beam Bridges

This paper presents an analytical study of the effects of diaphragms in I-beam bridges. The structures considered in the analyses are simple-span right bridges, consisting of a continuous slab supported by five uniformly-spaced parallel beams of equal stiffness, with the beams running in the direction of traffic. The diaphragms, which may be in the form of a channel, a WF-beam, or a built-up section, are transverse framings in the structure. Several variables are studied including (1) relative stiffness of diaphragm to that of each beam, (2) the position of diaphragms in the structure, (3) relative stiffness of beams to that of slab, (4) relative dimensions of bridge, and (5) the type and position of loading. The influence of the diaphragms on the behavior of the edge beam is also included.

From the results of the analyses, studies and comparisons are made to investigate the effects of different variables on the action of diaphragms in distributing the load on the bridge. The criteria of comparison is in general the maximum moment in beams produced by unit load or 4-wheel loading; with particular emphasis on the latter to simulate the actual loading condition. For one specific case, the analytical results are compared to those given for a fullsize field test. Conclusions and design recommendations with regard to the effective use of diaphragms in I-beam bridges are also presented.