Effect of shear stud clusters in composite girder bridge design

As part of ongoing efforts to accelerate bridge construction in Ontario, the Ministry of Transportation of Ontario (MTO) has turned increasingly to prefabricated bridge technology as a bridge construction method when conditions allow. One of the prefabricated deck systems commonly used by MTO involves installing precast full-depth deck panels with pre-formed shear pockets on top of the naked steel girders, which are then made composite with the girders through shear studs installed inside the shear pockets. Construction of the deck slab is completed by filling the shear pockets with in situ concrete. Recent prefabricated bridge projects have shown an increasing tendency to concentrate the shear studs into clusters of closely-spaced studs in shear pockets that are spaced at relatively large distances apart. Concerns have been raised about the effectiveness of the resulting composite action between the precast panels and the supporting girders. As a result, MTO’s Bridge Office recently carried out a comprehensive experimental research study to investigate the issue by using reduced scale models of single composite beam systems as well as shear push-out specimens. This paper describes the laboratory research project and the tests that were carried out and discusses the results obtained. Comparisons with theoretical results are made to assess the composite action that is developed. Experimental test results indicate that closely-spaced studs in the shear pockets in the precast deck panels provide adequate composite action in composite bridge girder design.