Dissertation Defence: Performance-Based Seismic Design for Retrofitting of Bridge Bents

Abu Obayed Chowdhury, supervised by Dr. Shahria Alam, will defend their dissertation titled “Performance-Based Seismic Design for Retrofitting of Bridge Bents” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil Engineering.

An abstract for Abu Obayed Chowdhury’s dissertation is included below.

Examinations are open to all members of the campus community as well as the general public. Please email shahria.alam@ubc.ca to receive the Zoom link for this exam.

---

ABSTRACT

An intended performance of a structure under different seismic hazard levels can be obtained by applying the performance-based seismic design (PBSD) approach. Various performance levels and the respective limit states need to be set for employing PBSD. These limit states corresponding to different performance levels are unavailable in the latest codes and guidelines for existing seismically deficient bridges having inadequate ductility and low shear strength. Being major components, multi-column bents have notable effects on the seismic behaviours of these bridges. Thus, a typical deficient bent is retrofitted, and developments of its limit states are sought in this research. Incremental dynamic analyses were performed in this study to come up with the limit states expressed in terms of limiting drifts and damage indices for different performance levels of retrofitted bents. This research adopted retrofitting techniques such as carbon fibre-reinforced polymer (CFRP), steel, engineered cementitious composite (ECC), and concrete jackets. Different retrofitted bents experienced various drifts at different performance levels. A detailed example has been developed to demonstrate retrofit design for achieving the target seismic performance with the proposed damage states. The comparative performances of all retrofitted bents in terms of noncumulative and cumulative damage measures were investigated for different hazard levels and earthquake sources. Drift and damage index, which considers how maximum drift and absorbed hysteretic energy simultaneously affect the performance, are adopted as noncumulative and cumulative ones, respectively. Evaluation of seismic loss in terms of life-cycle cost to retrofit a seismically deficient bridge bent is required in informed decision-making. Moreover, selecting an optimum retrofit techniques requires assessing the life-cycle cost as well as the bridge performance measured in terms of performance-based seismic resilience. The effects of various performance-based damage states and earthquake sources on life-cycle cost and seismic resilience were considered for retrofitting a deficient bridge bent in this research. Fragility analysis was conducted for achieving the conditional probabilities of exceeding various damage states at hazard levels with probabilities of exceedance of 10% and 2% in 50 years under various earthquake scenarios using the developed damage states in terms of limiting drifts. Performance-based seismic loss and seismic resilience assessments of as-built bent and bents retrofitted with different retrofit options were executed for life-cycle performance comparison and optimum retrofitting technique selection considering benefit-cost ratios, seismic resilience, and full-functionality recovery times. ECC jacketed bent had the least crushing probability in most situations. Furthermore, CFRP and steel jacketed bents were subjected to the smallest and highest seismic losses, respectively. ECC jacket was selected as the optimum option for retrofitting the deficient bent because it produced the greatest benefit-cost ratio under most conditions over the other techniques. All retrofitted bents exhibited the highest and lowest seismic resilience under interface and intra-slab earthquakes, respectively. Each retrofitted bent presented the minimum seismic resilience when the yielded rebar proportion mostly increased by 40% for intra-slab earthquakes. CFRP jacket also showed up as the optimum technique for retrofitting the deficient bent with maximum seismic resilience and shortest full-functionality restoration duration.