United States Department of Transportation
i
Repair of Earthquake-Damaged Bridge Columns with Interlocking Spirals and Fractured Bars
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2014-07-01
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[PDF-11.30 MB]
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Abstract: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. Although several repair options exist for columns with slight to moderate levels of damage, limited research has been reported in the literature for columns with fractured longitudinal reinforcing bars. A method that has shown success in restoring the strength and ductility to RC columns with fractured and/or buckled bars involves replacement of damaged longitudinal bars, reinstallation of transverse reinforcing bars, and restoring confinement using an external jacket. In some cases however, such as with seismically-designed RC columns with spiral reinforcement, it may not be possible to reinstall the internal transverse reinforcement. Thus alternative methods are needed to restore the performance of damaged RC columns with fractured bars to a desired state. The objective of this study was to develop methods to restore both the load and deformation capacity of earthquake-damaged bridge columns with interlocking spirals and buckled and/or fractured longitudinal reinforcement. The first repair method investigated was considered a permanent repair that involved replacement of the plastic hinge region by removal of spirals, replacement of longitudinal bar segments by mechanically splicing new bar segments attached with mechanical couplers, replacement of concrete, and installation of an externally bonded carbon fiber reinforced polymer (CFRP) jacket. The second method was considered an emergency repair that involved removal of damaged concrete, bonding and embedding CFRP strips for flexural reinforcement, building a jacket from a prefabricated thin 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 slow cyclic loading resulting in combined bending, 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; thus, the influence of the repair methods on the seismic response of bridges repaired with these methods is in need of further research.
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