Because changes in the structure's occupancy significantly affect the mass distribution and the structure's behavior, changing mass distribution might make the building more irregular and vulnerable to seismic ground motions. Many researchers tried to evaluate their seismic vulnerability. Most previous studies used simplified structural representations such as two-dimensional models that could not represent accurate seismic behavior from the coupling between lateral and torsional responses. For space structures with high irregularity, more realistic representations such as three-dimensional models are needed for the proper seismic assessment. To handle the computational challenge in deriving fragility curves, this research utilized a new structural reliability method that incorporates structural analysis and reliability analysis to efficiently and accurately calculate the failure probability with the first-order reliability method (FORM). This study investigates the seismic vulnerability of space-reinforced concrete frame structures with varying vertical irregularities. More representative seismic fragility curves are derived with their three-dimensional analytical models. The significant effect of the structure's vertical irregularity on seismic vulnerability is highlighted.
Skewed bridges are commonly used in highway interchanges where the straight (unskewed) bridges are not suitable. There have been several observations of heavy damage of bridges that have geometric irregularities, especially significant skewness. Such damage severely disrupts transportation systems, leading to substantial economic consequences. Skewed bridges are often inevitable due to the complexity and lack of orthogonality of transportation networks; hence better quantification of the effects of skewness on the bridge performance is a more viable approach than avoiding skewed bridges. This research focuses on the seismic vulnerability analysis of skewed reinforced concrete (RC) bridges. From the straight to highly skewed, various bridge models are created based on design example No. 4 prepared by the US Federal Highway Administration (FHWA). A set of earthquake ground motion records is carefully selected to impose consistent seismic demands on bridges. The fragility relationships for all bridge configurations are derived from the non-linear dynamic response history analysis. A new structural reliability method is utilized to handle the computational challenge in deriving fragility curves, which incorporates the structural analysis and reliability analysis to calculate the failure probability efficiently and accurately with the first-order reliability method (FORM). An attempt is made to parameterize the problem based on the skew angle. It is shown that the skew angle has a direct effect on the seismic vulnerability of RC bridges. The results reported will be helpful for new designs of skew RC bridges.
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