Seismic evaluation and retrofit of existing reinforced concrete bridge columns.
|Title:||Seismic evaluation and retrofit of existing reinforced concrete bridge columns.|
|Abstract:||Bridges like other important lifeline structures must remain in service when they are subjected to strong earthquakes. Many existing bridges, especially those built before the 1970s, are vulnerable to seismic damage since a number of deficiencies with regard to low design force levels, inadequate column confinement and lack of shear capacity were discovered during recent earthquakes. Bridge columns are expected to withstand seismically induced inertia forces without a significant loss of strength. This can be achieved in old columns through external retrofitting. Many reinforced concrete bridge columns in California were already retrofitted with steel jackets to enhance flexural ductility and shear resistance. Although this retrofitting technique is highly effective, it is also time consuming and costly, especially in view of the fact that high number of columns are yet to be retrofitted. Therefore, a new retrofitting technique has been developed through experimental research that involves external prestressing of bridge columns for improved deformability and shear strength. The supporting experimental work involved testing of 1485 mm high two 550 mm square and five 610 mm diameter circular cantilever columns. The columns were retrofitted with post-tensioned external hoops and high-strength steel straps at different spacing and stress levels. The results indicated that transverse prestressing of shear-dominant columns improved ductility and changed the mode of behavior from a brittle shear response to a ductile flexural behavior. The research project also included analysis of columns to establish lateral drift demands and capacities for bridge columns in Canada. A comprehensive survey of existing bridges in Canada was conducted to identify and classify common types of existing bridges in terms of their numbers, types, age, and structural and geometric properties. This information proved to be helpful in establishing column drift capacities and demands. A computer software DRAIN-RC, developed for non-linear dynamic analysis of reinforced concrete structures, was used to determine the drift demands of columns under various ground motions. Drift capacities were computed by a computer program COLA, developed by the author. The program COLA uses proper material models such as confinement of core concrete, extension of longitudinal reinforcement in tension, and buckling of re-bars in compression. The decision for retrofitting depended on the capacity of a column when demand exceeded its capacity.|
|Collection||Thèses, 1910 - 2010 // Theses, 1910 - 2010|