SEISMIC REHABILITATION OF REINFORCED CONCRETE BRIDGE COLUMNS IN MODERATE EARTHQUAKE REGIONS USING FRP COMPOSITES

摘要

Spectral design accelerations in the Northeast United States have significantly increased from previous values leading to higher seismic demands for structures constructed in this region. Under higher seismic demands bridge columns that were not designed to respond inelastically would now be expected to be able to accommodate inelastic displacements. More importantly, many of the bridges in the Northeast United States were designed before current earthquake design procedures were developed. Current seismic design practice of reinforced concrete structures promotes the use of adequate detailing to avoid premature failures of elements subjected to inelastic cyclic loading. Of particular concern are regions in structures where plastic hinges may form during the design seismic excitation. The main goal of the experimental research presented in this paper was to develop and evaluate a method to rehabilitate the plastic hinge region of bridge columns for expected inelastic displacement demands characteristic of the Northeast United States. Fiber-reinforced polymer (FRP) composite materials have been used in the past to retrofit the plastic hinge region of bridge columns in California. Because bridge columns in the Northeast States are not expected to undergo the same level of inelastic seismic demands as required in the West Coast, the amount of FRP material used in the retrofit can be potentially reduced. The retrofitting schemes reported in this study consist of using two types of FRP systems, carbon and aramid-fiber laminates, wrapped in the plastic hinge region of ? scale models of typical bridge columns constructed in the early 1960s in the Northeast U.S. The thickness of the laminates was designed to achieve a ductility level representative of regions of moderate seismicity. The results indicate that economical retrofitting techniques using FRP jackets can be used to improve the seismic performance of bridge columns by increasing confinement and avoiding lap-splice failures near the base of existing columns.