Load distribution and connection design for precast stemmed multibeam bridge superstructures

This report describes research on distribution of wheel loads in precast concrete multibeam bridges made from single and multi-stemmed members. It covers two distinct areas. In the first, wheel load fractions for the design of individual members were obtained. This was done by computing the maximum response to truck loading of a large number of different bridges. A grillage method, modified to account for the effects of warping, was used, and was first checked against closed-form solutions and values measured in full-scale laboratory tests. The wheel load fraction was found to be expressible in a form very similar to that presently used in the AASHTO Specifications, to which changes are proposed. The second area covered design of the joints between members, which are typically made with steel connectors and a grout key. The research consisted of an extensive literature search, the development of a proposed design methodology for the steel connectors and a series of laboratory tests. It was found that the grouted keyway is much stiffer than the steel connectors and carries essentially all the shear load before it cracks. Estimates were made of the joint forces to be expected in a bridge in the field, but these were found to be very sensitive to the modelling used. Recommendations are made for a better keyway geometry and for design of the steel connectors.