In the field of earthquake engineering, Fragility Curves (FCs) have become indispensable for regional risk assessments due to their efficacy in estimating the failure probabilities of diverse structures, including buildings and bridges, based on certain intensity measures. FCs are typically derived from either mechanical simulations or on -site observations, encapsulating crucial information about local stratigraphy and topography. The dependency of FCs on these local parameters, such as soil and topographic conditions, may vary depending on the selected intensity measure. When a spectral ordinate at a specific period is used as an intensity measure, FCs tend to be largely site -independent. On the other hand, if the intensity measure is chosen to be the acceleration ag at the bedrock substrate, as often occurs, then the FC is site -dependent. This distinction implies that identical structures at different locations, or even the same location with different soil and topographic conditions, have different FCs. This can significantly influence the results of regional risk studies, as using FCs for a specific building type at diverse locations with different hazards, stratigraphy, and topography can result in significantly different failure probabilities. The goal of this study is to develop a method so that ag-based FCs, developed at a certain location, can be used at any other location and on any other soil, preserving consistency in terms of spectral ordinate. This is done by a fully analytical approach, using a spectrum -consistent transformation. As an application, risk maps for Italy are generated and compared with an alternative method based on shifting the hazard curve.

The amplification of seismic waves due to surface topography and subsurface soils is a significant factor contributing to seismic site amplification and consequent damage. However, conventional deterministic analysis methods can hardly account for the impact of inherent spatial variability of subsurface soil properties. This study employs a random finite element method (RFEM) to address this limitation and investigate the amplification of ground acceleration in time and frequency domains for 2D slope models with varying magnitudes of soil elastic modulus (E) and coefficients of variation (COVs). Comprehensive insights are provided through the analysis of amplification indicators related to peak ground acceleration, Fourier spectrum ratio, and response spectra of input motion. It is found that the spatial variability of E reduces the maximum amplification factor (AF) at the slope crest. Frequency domain analyses show that considering spatially variable E leads to decreasing trends in Fourier spectra and mean values of the transfer function, especially in the mid-to-high-frequency range. However, transfer functions for topographic effects exhibit high-frequency amplification in models with a higher impedance ratio. For the response spectra, the topographic amplification factor (TAF) and spectra amplification factor (SAF) at longer periods gradually increase in random simulations, indicating the potential risk for long-period structures. The findings emphasize the significance of spatial variability in soil properties for seismic amplification, providing probabilistic insights for seismic design and optimization in complex site conditions.

To elucidate the effect of canyon topography on dynamic response of a bridge, an analytical model for a simply supported bridge crossing a symmetric or non-symmetric V-shaped canyon in an elastic half-space under SH waves is proposed. An exact solution to the dynamic canyon-bridge interaction problem is derived using wave function expansion and verified by its comparison with past exact solution for a sole bridge model without a canyon. The wave propagation in the half-space, wave scattering by the canyon and wave radiation from the bridge are all taken into account rigorously. Through a systematical parametrical study, it is found that the seismic response of the bridge beam and the wave-facing side foundation will be significantly amplified. The degree of the topographic amplification is closely related to the geometry of the canyon, the mass and the stiffness of the bridge beam, and the frequency content and angle of the incident wave. The potential adverse effects of a V-shaped canyon on a bridge should be considered in its seismic design.