A Methodology for Probabilistic Performance-Based Seismic Risk Assessment of Bridge Inventories.

摘要

Over the past several decades, many structural lessons have been learned from disastrous seismic events resulting in major advances in the understanding of seismic response behaviour and performance of bridges. Over the years, these advances and improved design methods have been implemented in numerous revisions of bridge design standards. From damage observations and analysis, various deficiencies, in terms of seismic performance, have been identified in bridges designed based on specifications from bridge design standards from different time periods. Knowing there are seismic deficiencies in our existing aging infrastructure, it is important to have a methodology to evaluate and quantify the seismic risk and vulnerability of the existing bridge systems. In current state-of-practice, individual bridges of high priority are selected for detailed examination and review of their structural integrity. However, due to the large number of bridges involved and the limitation of resources available, there is a need to prioritize what bridges undergo complete structural reviews and possible rehabilitations. This is done through physical site inspections and assessments by computer structural analysis. Although this approach gives detailed information on the risk of individual bridges, it does not give high level assessment information on the risk and vulnerability of the entire bridge infrastructure from a system perspective. Probabilistic performance-based seismic risk assessment methodologies can be used to identify the probable performance of selected bridges. The probabilistic framework involves four interim steps of site hazard analysis, structural response analysis, damage analysis and loss analysis. It requires the evaluation of the seismic hazard at a bridge site, the analysis of the bridge responses to ground motion excitations compatible with the seismic hazard, the probability of damage associated with the calculated responses by using fragility curves, and the evaluation of losses resulting from expected damage levels. In this study, the probabilistic performance-based seismic risk assessment methodology has been adapted and further developed to formulate a new evaluation approach suitable for quick assessment of large bridge inventories in a city, regional or national network. The new quick assessment approach does not require detailed non-linear time history analysis of all evaluated bridges. Nonlinear time-history analysis of selected representative bridges has been carried out to calibrate the quick assessment methodology. Fragility relationships relating potential or probability of damage to easily identified or determined structural performance characteristic parameters of evaluated bridges are developed.;In collaboration with the City of Ottawa, a pilot study of seismic risk assessment of a sample inventory of bridges has been conducted by using the new quick assessment methodology. From the assessment results, an order or priority list of bridges can be established. The system perspective information and assessment results would help with better decision making on resource allocation for more efficient and effective bridge infrastructure maintenance and management.