Precast prestressed concrete bridges with debonded strands

This thesis summarizes an experimental investigation carried out to evaluate the effects of strand debonding on the load carrying capacity of composite precast pretensioned bridge members with a cast-in-place concrete slab. Four continuous and five simply supported specimen sets were fabricated and tested in this study. Shear as well as flexural capacity were studied and the experimental results were compared to the results obtained using analytical methods. Three of the continuous specimens consisted of two precast Type-I AASHTO girders with a composite cast-in-place slab and diaphragm. The fourth specimen consisted of two Type CB-27 box girders also continuous with cast-in-place slab and diaphragm. The effects of time-dependent creep and shrinkage deformations on the capacity of the girders at the continuous supports was investigated in this study. Also addressed in this study is the effect of limiting the stress at the extreme compression fiber, near the continuous supports to allowable working stress values on the load carrying capacity of continuous members. After each continuous test, the continuity between the two beams was broken, each beam of the corresponding specimen set was further tested to failure over a simply supported span. The test beams in each simply supported specimen set were identical except for the strand debonding schemes near the ends. In each set, one beam had the strands bonded throughout the entire length. The other one had some percentage of the strands debonded near the ends. The results from these tests were used to examine current ACI/AASHTO requirements for flexure and shear design of pretensioned bridge girders with debonded strands. The behavior of the pretensioned beams was explained using the strut-tie approach. The effect of strand debonding and anchorage were modeled using this approach. Strut-tie models which incorporated the influence of shear transfer along cracks and concrete tension stiffening offered clear behavioral concepts and were in reasonable agreement with the experimental results