Reducing Earthquake-induced Damage to Precast Concrete Bridge Piers

Abstract

Precast concrete is under-utilized in seismic regions. This dissertation will discuss methods for reducing earthquake-induced damage to precast concrete piers to enable deployment of accelerated construction in the regions of moderate-to-high seismicity. Limitations of existing precast pier systems will be addressed and development of novel precast pier systems will be presented.Unlike emulative precast concrete systems, non-emulative precast concrete systems are not expected to behave like cast-in-place concrete. They can achieve self-centering and overall damage control through developing rocking. Seismic damage in these systems is primarily in two forms: concentrated concrete spalling and post-tension loss. To minimize this damage, Ultra-High Performance Concrete (UHPC) with and without mild-reinforcement is used in the damage-prone regions of rocking precast piers. Large-scale test results demonstrated that UHPC is able to control seismic damage near the rocking plane, even without any mild-reinforcement. To address post-tension loss, tests were performed on strand-anchorage assemblies under cyclic load and an analytical method was proposed to predict strand constitutive properties and post-tension loss. Shear-slip was investigated as an energy dissipation source. A simplified hysteretic model was developed as an effective tool for designing with this energy dissipation method.In addition to investigating non-emulative systems, analytical studies were performed to understand if UHPC can be used for emulative systems that mimic cast-in-place concrete. Although UHPC has the potential to control damage stemming from the formation of plastic hinges, it has limited flexural ductility. The analytical studies addressed this issue by using high-strength steel confinement in UHPC to improve flexural ductility. The impact of confinement on UHPC on hollow cross-section columns was investigated.A new hybrid, post-tensioned precast segmental pier was proposed to combine emulative and non-emulative joints to balance energy dissipation and self-centering. A performance-based design procedure based on a computationally efficient analytical model was developed to select design parameters and to accommodate UHPC. The material properties of UHPC were selected through material-scale testing of commercially available UHPC products. A set of large-scale quasi-static test results showed that this system can strike a balance between self-centering and energy dissipation, and that damage due to bending can be alleviated when UHPC replaces conventional concrete. A finite element model, validated by test results, was used to understand the impact of varying design parameters on the seismic response of this hybrid precast pier system.