Date of Award
Master of Science
Civil, Construction, and Environmental Engineering
Accelerated Bridge Construction (ABC) utilizing precast components continues to be used as an effective tool for bridge construction due to time and cost saving techniques as well as the reduction of environmental impacts. However, in seismic regions, the use of precast members and ABC methods are limited due to concerns about poor performance of connections primarily between cap beam and girders. With sponsorship from the California Department of Transportation (Caltrans), two alternative connections between precast bulb tee girders and bridge cap were designed utilizing extended girder prestressed strands. The connections were designed to resist positive moments at the girder to cap connection. Positive moments occur at the connection when seismic forces cause upward deflection of the precast girders resulting in tension forces along the bottom of the girder to cap connection. The tension forces cause damage to the connection and can also unseat or disconnect the girders from the cap beam resulting in span collapse. The two connections were designed to minimized connection damage and prevent unseating of the girders. In one connection the extended strands were curved and relied on bond strength for anchorage along the 60 in. embedment length. The other connection consisted of spliced strands with anchor plates and chucks which relied on the transfer of forces through strand splices. Both connections also included three grouted dowel bars placed through the girder web. The connections were designed to provide adequate seismic moment resistance up to a combined load of gravity, horizontal ground acceleration corresponding to the column overstrength moment, as well as shear and moment values up to 0.5g vertical acceleration. A 40% scale test unit was constructed in the Iowa State University structures laboratory and the two connections were tested. An analytical model was formulated to analytically quantify the behavior of each connection. The results of the tests showed that both connections had adequate capacity to resist horizontal and vertical ground acceleration forces as specified in current Caltrans seismic design criteria. Adjustments were made to the analytical model based on results of the test to improve the accuracy of the model. The overall results of the test demonstrate that ABC methods can be safely implemented in high seismic regions and be relied upon for dependable performance.
Peggar, Robert, "Two integral girder connections for precast concrete bridges in seismic regions utilizing extended prestressing strands" (2014). Graduate Theses and Dissertations. 14233.