Seismic repair of bridge columns with interlocking spirals and fractured bars

During earthquakes, reinforced concrete (RC) bridge columns may experience different levels of damage such as cracking, spalling, or crushing of concrete and yielding, buckling, or fracture of reinforcing bars. This study developed and assessed permanent and emergency methods to repair damaged bridge columns with fractured longitudinal reinforcement through experimental and modeling work. The permanent repair method involved replacement of the plastic hinge region by removal of spirals, replacement of longitudinal bar segments by mechanically splicing with new bars segments attached with mechanical couplers, replacement of concrete, and installation of an externally bonded carbon fiber reinforced polymer (CFRP) jacket. The emergency repair method involved removal of damaged concrete, bonding and embedding CFRP strips for flexural reinforcement, building a jacket from a prefabricated CFRP laminate, and repair of the footing with CFRP fabric. The repair methods were evaluated by large-scale component tests on RC column specimens subjected to constant axial loading and slow cyclic loading resulting in combined flexure, shear, and torsion. Test results showed that the repair methods developed in this study are capable of restoring the seismic performance of the repaired columns to that of the undamaged columns in terms of lateral load and deformation capacity, as well as torsional load and twist capacity. However, both repair methods resulted in lower lateral and torsional stiffness as well as lower energy dissipation capacity. Three-dimensional truss models were developed to simulate the as-built and repaired columns and showed efficiency and accuracy in predicting the response of columns under combined cyclic loading including torsion --Abstract, page iii