Factors affecting the efficiency of repair to propped and unpropped bridge beams

This paper presents the results of laboratory and field investigations of bridge beams repaired both under propped and unpropped conditions. In the laboratory, beams were repaired using hand-applied repairs. Repairs to beams in two highway bridges were carried out using both hand-applied and flowing repairs. The repair materials used were commercial products of wide-ranging properties (shrinkage, creep and elastic modulus). Both low stiffness repair materials of elastic modulus, E_rm, less than the substrate E_sub, and high stiffness repair materials (E_rm > E_sub) were used. The repairs were applied in the tensile zone of the beams. Strain distributions in the different phases of repair patches were monitored under service loading for a period of up to 240 weeks. The results show that high structural efficiency is achieved with repairs having E_rm > E_sub, other properties (shrinkage and creep) being within reasonable limits. Such repairs are less prone to restrained shrinkage cracking and show a capacity for load redistribution into the repair patch. Low stiffness repairs (E_rm < E_sub), on the other hand, are prone to restrained shrinkage cracking and are ineffective in load-sharing with the substrate. Repairs to propped flexural members developed erratic and non-uniform load distribution in the different phases upon reapplication of load. Composite action between the repair patch and the substrate results in cracking in the repair patch, rendering the repairs structurally inefficient.