Seismic evaluation and retrofit of concrete bridge columns and joints

Reversed cyclic loading tests were carried out on a number of specimens including five half-scale reinforced concrete bridge columns with one and two-way hinges at the column-footing connection, a half-scale column with lap-spliced dowels at its base and a quarter-scale outrigger beam-column-joint. The test specimens had details typical of bridges designed and built in Montreal in the 1960's. These tests highlighted the design and detailing deficiencies and demonstrated the poor seismic performance of the "as-built" structural elements. Procedures and guidelines for retrofitting were developed for moderate seismic regions and were applied to the test specimens. The reversed cyclic loading responses of these retrofit specimens demonstrated the improved strength, ductility and energy dissipation of the retrofits.Analytical techniques are described which result in accurate response predictions for both the "as-built" and the retrofit elements. A series of compression tests on concrete hinges permitted the development of a model to assess the influence of confinement on the stress-strain characteristics of the hinge region concrete. The response predictions included the effects of confinement of concrete hinges, bond slip, shear distress, presence of lap splices and poor anchorage details. Static analyses were performed according to the 1996 Canadian Highway Bridge Design Code (CHBDC) to determine the seismic responses of prototype structures and to determine if retrofit is required. Non-linear dynamic analyses were performed with three input ground motions to predict the responses of the "as-built" structures and to assess the performance of the retrofit structures. These analyses identified the deficient structural systems and demonstrated that the retrofit techniques developed were effective in significantly improving the seismic responses