Probabilistic Seismic Damage Assessment for Sub-standard Bridge Columns
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Probabilistic and statistical analyses of sub-standard bridge columns constructed prior to the development of the current seismic design codes have not been addressed in the literature. Most of the previous studies on the seismic performance of sub-standard columns were focused on development of retrofit and repair methods. The main objective of the present study was to develop a practical method for reliability-based seismic assessment of sub-standard bridge bents that are yet to be retrofitted. The study consisted of development of a capacity (resistance) and a demand (load) model for sub-standard bridge bents and reliability analysis to determine the extent of their seismic vulnerability. To develop the capacity model, detailed data from previous experimental studies of 25 bridge column models was reviewed and analyzed, four distinct apparent seismic damage states were identified, and a response parameter (referred to as damage index) was defined in terms of demand and ultimate displacement capacity. To correlate the damage states with damage index, the column data were combined and load distribution curves were developed using fragility relationships. The demand model was developed through analytical modeling of a large number of single-, two-, and four-column bents including a practical range of the number of columns per bent, support conditions, aspect ratios, longitudinal steel ratios, lap-splice lengths, ground motion types, site classes, and earthquake return periods. A new simple analytical method was developed to account for the effects of the slippage of spliced bars on the response of the bents. To determine the demand damage indices, extensive pushover and nonlinear dynamic analyses were performed. Potential shear failure was also implicitly accounted for in the analyses. The demand model was established using load distribution curves developed based on fragility relationships of demand damage indices. Utilizing the distribution of the capacity and demand models, reliability against failure and other damage states was determined incorporating the probability of earthquake exceedance during the lifetime of bridges. The results of reliability analysis were summarized and an illustrative example on the application of reliabilities in seismic assessment of sub-standard bridge bents was presented.
Report No. CCEER-16-06