Effects of structural characterizations on fragility functions of bridges subject to seismic shaking and lateral spreading

This paper evaluates the seismic vulnerability of different classes of typical bridges in California when subjected to seismic shaking or liquefaction-induced lateral spreading. The detailed structural configurations in terms of superstructure type, connection, continuity at support and foundation type, etc. render different damage resistant capability. Six classes of bridges are established based on their anticipated failure mechanisms under earthquake shaking. The numerical models that are capable of simulating the complex soil-structure interaction effects, nonlinear behavior of columns and connections are developed for each bridge class. The dynamic responses are obtained using nonlinear time history analyses for a suite of 250 earthquake motions with increasing intensity. An equivalent static analysis procedure is also implemented to evaluate the vulnerability of the bridges when subjected to liquefaction-induced lateral spreading. Fragility functions for each bridge class are derived and compared for both seismic shaking （based on nonlinear dynamic analyses） and lateral spreading （based on equivalent static analyses） for different performance states. The study finds that the fragility functions due to either ground shaking or lateral spreading show significant correlation with the structural characterizations, but differences emerge for ground shaking and lateral spreading conditions. Structural properties that will mostly affect the bridges＇ damage resistant capacity are also identified.

Performance-based seismic assessment of a large diameter extended pile shaft in a cohesionless soil

The seismic behavior of a large diameter extended pile shaft founded on a dense sandy site is investigated in this paper. First, a deterministic analysis is conducted including both nonlinear dynamic analysis （NDA） and pushover analysis to gain insights into the behavior of the pile and make sure an appropriate modeling technique is utilized. Then a probabilistic analysis is performed using the results of NDA for various demands. To this end a set of 40 pulse-like ground motions are picked and subsequently 40 nonlinear dynamic and pushover analyses are performed. The data obtained from NDA are used to generate probabilistic seismic demand model （PSDM） plots and consequently the median line and dispersion for each plot are computed. The NDA and pushover data are also plotted against each other to find out to what extent they are correlated. These operations are done for various engineering demand parameters （EDPs）. A sensitivity analysis is done to pick the most appropriate intensity measure （IM） which would cause a minimum dispersion in PSDM plots out of 7 different IMs. Peak ground acceleration （PGA） is found to be the most appropriate IM. Pushover coefficient equations as a function of PGA are proposed which can be applied to the pushover analysis data to yield a better outcome with respect to the NDA. At the end, the pacific earthquake engineering research （PEER） center methodology is utilized to generate the fragility curves using the properties obtained from PSDM plots and considering various states of damage ranging from minor to severe. The extended pile shaft shows more vulnerability with a higher probability with respect to minor damage compared to severe damage.