This study quantifies the seismic fragility assessment of shallow-founded buildings in liquefiable and treated soils, enhanced by drainage and densification, considering both short-and long-term behaviors. A conceptual framework is proposed for developing seismic fragility curves based on engineering demand parameters (EDPs) of buildings subjected to various earthquake magnitudes. The framework for establishing seismic fragility curves involves three essential steps. First, nonlinear dynamic analyses of soil-building systems are performed to assess both the short-term response, which occurs immediately following an earthquake, and the longterm response, when excess pore water pressure completely dissipates, and generate a dataset of building settlements. The seismic responses are compared in terms of excess pore water pressure buildup, immediate and residual ground deformation, and building settlement to explore the dynamic mechanisms of soil-building systems and evaluate the performance of enhanced drainage and densification over short-and long-term periods. Second, 38 commonly used and newly proposed intensity measures (IMs) of ground motions (GMs) are comprehensively evaluated using five statistical measures, such as correlation, efficiency, practicality, proficiency, and sufficiency, to identify optimal IMs of GMs. Third, fragility curves are developed to quantify probability of exceeding various capacity limit states, based on structural damage observed in Taiwan, for both liquefaction-induced immediate and residual settlements of buildings under different levels of IMs. Overall, this study proposes a rapid and straightforward probabilistic assessment approach for buildings in liquefiable soils, along with remedial countermeasures to enhance seismic resilience.

Historical data has shown that soil-structure systems exhibit increased severity when subjected to earthquake sequences, attributed to the accumulated instability of soil deposits and the cumulative damage of structures. This study analyzes seismic responses of multi-story buildings and mechanical behavior of liquefiable soil deposits under repeated shake-consolidation process. This is achieved through a series of numerical simulations using a finite element-finite difference (FE-FD) code, namely DBLEAVE-X. Sequential earthquakes are obtained from the NGA-West2 PEER ground motion database and recalibrated relied on various aspect ratios, including peak ground acceleration ratios (rPGA) and consolidation time (Tgap). The numerical results reveal that shearinduced and residual settlements of buildings during sequential earthquakes might be notably larger than that during single earthquakes. The repeated shake-consolidation process has a significant impact on development and dissipation of excess pore water pressure (E.P.W.P), notably influencing the deformation response of both buildings and ground deposits. The findings also provide valuable insights into effects of both complete and partial consolidation processes on seismic mechanisms of entire liquefiable soil-structure systems. Numerical observations suggest that multi-story buildings under sequential earthquakes might be more vulnerable, underscoring the necessity of integrating sequential earthquakes into earthquake-resistant building design.

In earthquake-resistant design, amplitude and frequency content of ground motions (GMs) have been considered using spectral matching techniques; however, duration effects remain insufficiently explored in designing buildings in liquefiable soils. This study investigates the influence of ground-motion duration on seismic response of shallow-founded buildings under strong earthquakes. Buildings in liquefiable soils are analyzed using nonlinear dynamic analysis with coupled u-p formulations. The numerical code and calibrated constitutive parameters of Toyoura sand are validated through dynamic centrifuge testing. Two ground-motion suites, including 30 pairs of long and short-duration events, are scaled to the target PGA of 0.3 g, and then selected to be spectrally equivalent to isolate duration measures from the others. Comparative results show that longer duration events result in greater settlements and tilt compared to shorter events. Therefore, this study emphasizes the importance of considering duration measures in assessing seismic responses of buildings. Furthermore, correlation between settlements and peak transient tilt, and intensity measures (IMs) of GMs are comprehensively analyzed. It is found that employing compound IMs can lead to notable improvements in predictive accuracy for settlement and peak transient tilt compared to single common IMs. The compound IMs, namely CAV2/3 x Ds5-951/3 and SMV x Ds5-95 3, are newly proposed for use in order to achieve best correlation with the shear-induced settlements and peak transient tilt, respectively.