Structural deterioration and time-dependent seismic risk analysis [electronic resource]
Keywords: Civil and Environmental Engineering.

Deterioration of built infrastructure is growing into a major cause of concern for countries with a large population of aging structures. Although seismic design standards continue to advance as lessons learned from past events get incorporated, structures designed to older standards are likely to be more vulnerable to damage during earthquakes. The poor seismic performance of older structures is likely to be further exacerbated by advanced levels of structural deterioration, which may be caused due to a variety of processes such as chloride-induced corrosion, alkali-silica reaction, sulfate attack, freeze-thaw cycles, carbonation, and fatigue. However, the effects of long-term structural deterioration have been traditionally neglected in seismic risk assessment. This dissertation focuses on the development of a comprehensive methodology for the time-dependent seismic risk assessment of structures located in a multi-hazard environment, that can explicitly account for the effects of (1) the time-varying nature of the different hazards, (2) long-term structural deterioration, and (3) cost escalation and the time-value of economic resources on seismic loss and impact estimates. The methodology for time-dependent seismic risk analysis proposed in this dissertation begins with the PEER framework as a starting point and extends it through the addition of a separate module for time-dependent probabilistic deterioration analysis. Explicitly accounting for deterioration within the proposed framework requires probabilistic models for predicting the time-dependent level of deterioration of structural elements. The steps involved in estimation of the time-dependent degree of deterioration for the case of deterioration in reinforced concrete bridge columns due to chloride-induced corrosion are illustrated in this dissertation, using available empirical models to describe the multi-stage corrosion process. In order to account for the effects of structural deterioration within the proposed framework, the seismic fragility of structural components is modeled as a joint function of the ground motion intensity measure, and the degree of deterioration. Calculation of these deterioration-dependent component fragility functions requires predicting the change in both damage state capacities and seismic demands due to deterioration. The use of a simple, single parameter exponential decay function is proposed to model the decrease in median damage state fragilities with increase in the degree of deterioration. The deterioration-dependent component fragility functions can be integrated with the results from probabilistic time-dependent deterioration analysis, or with actual measurements of the level of deterioration obtained during inspection, at a later stage within the proposed framework to obtain a time-dependent description of the seismic risk. Finally, the proposed methodology for time-dependent seismic risk assessment is used to conduct a comprehensive study of the life cycle costs and environmental impacts of three deteriorating California highway bridge columns. Such a comprehensive evaluation of time-dependent environmental impacts associated with repairs following an earthquake for deteriorating structures located in an evolving multi-hazard environment is the first of its kind.