Shear behavior of full-scale post-tensioned prestressed concrete bridge girders

The shear behavior of prestressed concrete girders is one of the most important factors in the rational design of those structures. The test data on the shear behavior of full-scale post-tensioned prestressed concrete girders are very limited. The purpose of the present study is, therefore, to experimentally explore the shear behavior of post-tensioned prestressed concrete girders. To this end, large-scale post-tensioned prestressed concrete girders are fabricated using medium-high and high-strength concretes. Full-scale post-tensioned girders that are 1.2 m deep and 10.6 m long are designed, fabricated, and tested. The girders were tested up to failure while deflections, steel stirrup strains, cracking pattern, and average strains in the web were monitored. The strain gages attached along the height of several stirrups make it possible to observe the occurrence and propagation of diagonal cracks in the shear region. The stirrup strains show a sudden increase immediately after cracking and continue to grow as the load increases. To measure the average strains in three directions, triangular grids of linear variable differential transducers (LVDTs) were also placed at the shear region of girders. These LVDTs enable to measure the average strains in the vertical, longitudinal, and diagonal directions even after the diagonal cracking has occurred. Shear strains, principal strains, and principal directions are calculated from these measured average strains. It is found that the angle of principal strain direction decreases as the applied load increases and that it approaches to approximately 23 to 25 degrees at ultimate load stage. The concept of average strains and the change of principal direction investigated in this study can be used for a more accurate shear analysis of post-tensioned prestressed concrete girders.