Simulation and performance-based earthquake engineering assessment of self-centering post-tensioned concrete bridge systems.

摘要

In recent years, the earthquake engineering community has focused attention on Performance-Based design in order to predict and manage better the post-earthquake functionality and condition of structures. The focus of this research is on bridges, and in particular, bridge columns. Standard highway bridges in highly seismic regions are typically designed such that plastic behavior will concentrate in the columns during earthquakes. The columns are expected to undergo large inelastic deformations during severe earthquakes, which can result in permanent, or residual, displacements. These residual displacements are an important measure of post-earthquake functionality in bridges, and can determine whether or not a bridge remains usable following an earthquake. To mitigate the effects of residual displacements, a number of systems for concrete highway bridges using unbonded, post-tensioned reinforcement for providing self-centering to the columns are proposed and investigated.; The first objective of this research is to assess and develop simulation methods and models where needed that can accurately capture key performance attributes of reinforced concrete and unbonded, post-tensioned concrete bridge piers, to facilitate their comparison. The second objective is to provide a systematic assessment of various self-centering systems using unbonded post-tensioning for concrete highway bridge columns in seismic regions. The assessment is performed by quantitatively comparing the seismic performance of the new systems to current code-conforming, conventional reinforced concrete highway bridges both in terms of engineering response as well as more readily understood metrics such as expected repair costs and downtime. In this way, the performance of code-conforming highway bridges can also be benchmarked. The third objective is to evaluate the performance-based assessment methodology itself.; The unbonded post-tensioned systems were found to perform comparably to the conventional reinforced concrete system in terms of peak drifts. Reductions to column damage in the case of some of the systems were found not to justify their higher initial costs. However, the unbonded post-tensioned columns sustained considerably lower residual drifts than the reinforced concrete columns, leading to significant reductions in expected bridge downtime following large earthquakes. These significant reductions in downtime make the unbonded post-tensioned systems desirable for important bridges that must remain operational following an earthquake.