Extreme Bridge Loads
Full Session with Abstracts
340050-5 - Analytical models for seismic repair of bridge columns using plastic hinge relocation
Friday, April 20
1:30 PM - 5:00 PM
A repair technique for two severely damaged reinforced concrete (RC) bridge columns has been developed that utilizes a carbon fiber-reinforced polymer (CFRP) shell and epoxy anchored headed steel bars to relocate the column plastic hinge. Two specimens, each composed of a column and cap beam, were tested. For the first specimen, which was cast-in-place concrete, the column had achieved a 10% drift ratio with severe damage including buckling and fracture of longitudinal steel bars, and concrete crushing. The second specimen was precast concrete and was already repaired once; extensive cracks widened in the column of this specimen and was repaired for a second time to improve performance. The plastic hinge was successfully relocated, the lateral force and displacement capacity were restored, and failure of the repaired columns included concrete crushing and/or steel bar fracture. Analytical models are presented to predict the seismic performance of the repaired specimens. Two models, Model PH and Model RS are proposed. In Model PH, distributed plasticity considering bond slip is assumed to be concentrated in a plastic hinge length of the nonlinear beam-column element instead of the whole length of the element; this was implemented using the BeamWithHinges element in OpenSees. An axial stress versus loaded-end displacement model of damaged longitudinal steel bars, including both elongation and bond-slip effects, is derived from a 1-D non-linear truss bond slip model to consider the slip of longitudinal steel bars in the plastic hinge region adjacent to the repaired section. The simplified model is then converted to an equivalent stress-strain relationship and is implemented in the fiber element model. In Model RS, concentrated plasticity was considered using a non-linear moment-rotation spring located at the repaired cross-section. A sectional moment-curvature analysis is performed, based on damaged steel properties and considering bond slip, to obtain the moment-rotation relationship for the non-linear spring. Both analytical models proposed in this paper include low-cycle fatigue of longitudinal steel bars and bond-slip effects. Numerical simulations show that the analytical results, in terms of hysteretic response, cumulative hysteretic energy, and bending moment-rotation agree with the experiments. Comparisons between numerical simulations and experimental results indicate that Model PH predicts better the pinching effect in the hysteretic response of the repaired cast-in-place specimen than Model RS; Model RS matches better the hysteresis curves of the repaired precast concrete specimen than Model PH. The analytical models confirm the significant effect of bond-slip of the longitudinal steel bars on the seismic performance of the repaired specimens. It is found that the bond between the original column concrete and repair concrete is crucial in the overall structural performance of the repaired specimens.