Cloud and incremental dynamic analysis (IDA) are the two most commonly used methods for seismic fragility analysis. The two methods differ significantly in the number of ground motions and whether these motions are scaled. This paper designed a random selection procedure to thoroughly discuss the influence of ground motion combinations encompassing different numbers of motions on the Cloud-based and IDA-based seismic fragility analysis for underground subway station structures. Focusing on a shallow-buried single-story station structure, a nonlinear dynamic time-history finite element analysis model of soil-structure interaction was developed. 400 ground motions were selected for random combination to perform Cloud-based seismic fragility analysis, and 20 ground motions were selected for random combination to perform IDA-based analysis. The results showed that the number of ground motions has a significant influence on the seismic fragility analysis in both Cloud and IDA, especially on the prediction of damage probability for higher seismic performance levels and when the PGA exceeded 0.3 g. In regions with a low probability of strong earthquakes, this paper recommended using no fewer than 10 and 220 ground motions in the IDA-based and Cloud-based seismic fragility analyses, respectively. In regions with a high probability of strong earthquakes, the optimal number of ground motions should be increased to 300 for Cloud-based analysis and 15 for IDA-based analysis.

Nepal, a landlocked country in the Himalayan region, was struck by a devastating earthquake of magnitude Mw 7.8 on 25th April, 2015. The major earthquake destroyed millions of structures and caused immense loss of life. Unfortunately, only a few seismic stations recorded the earthquake, presenting a challenge for understanding the observed non-uniform structural damage in the region. In this study, synthetic ground motions are generated at the bedrock level using the stochastic finite fault method. The ground motions are later estimated at the surface level using the equivalent linear site response analysis program, using soil profiles from 9 borehole locations from the Kathmandu basin. The key characteristics of the synthetic strong ground motions are tabulated and analyzed. Peak ground accelerations (PGA) at bedrock in the region range from 0.064 g to 0.09 g. Remarkably, the Kankali site (BH6) exhibits the highest outcrop acceleration response, with bedrock and outcrop PGAs measuring 0.083 g and 0.170 g, respectively. Observations indicate that soil profiles experience their greatest amplification ratio within the frequency range of 1.2 Hz-7.3 Hz. Plots of response spectra for the synthetic ground motions are derived and compared with the provisions of the Nepal's seismic design code. The key characteristics of strong ground motions and observations from the derived response spectra correlate well with the available reports of structural damage in the earthquake. These observations provide valuable insights into seismic vulnerability and soil behavior that is crucial for seismic hazard assessment and engineering design considerations.

In the processes of seismic design of underground structures, selecting a reasonable input ground motion is very important, which can cause severe damage to underground structures. To quantitatively evaluate the seismic damage potential of ground motions on multi-storey underground structures and solve the problem that single intensity measures are inadequate in accurately indicating the seismic damage potential of ground motions, this paper taking the input ground motions in the seismic design of underground structures as the research object, and constructing some composite intensity measures that can effectively characterize the damage potential of input ground motion. Firstly, considering that the underground structures in different characteristic period-type sites will exhibit different seismic responses under the same excitation, the soil-structure system is divided into four-period bands. Then, four representative periods are selected from four-period bands respectively, and the corresponding four soil-structure system numerical models are established. Subsequently, 40 ground motions are selected for elastoplastic numerical analysis, and the results of the numerical analysis were used as sample data to construct composite intensity measures corresponding to soil-structure systems in each period band using the partial least squares regression method. Finally, 100 additional ground motions were used to verify the correlation between the composite intensity measures and the seismic damage of underground structures. The results show that the correlation coefficient between the composite intensity measures and the seismic damage of multi-storey underground structures is better than those of commonly used single intensity measures.

Prediction of the intensity of earthquake-induced motions at the ground surface attracts extensive attention from the geoscience community due to the significant threat it poses to humans and the built environment. Several factors are involved, including earthquake magnitude, epicentral distance, and local soil conditions. The local site effects, such as resonance amplification, topographic focusing, and basin-edge interactions, can significantly influence the amplitude-frequency content and duration of the incoming seismic waves. They are commonly predicted using site effect proxies or applying more sophisticated analytical and numerical models with advanced constitutive stress-strain relationships. The seismic excitation in numerical simulations consists of a set of input ground motions compatible with the seismo-tectonic settings at the studied location and the probability of exceedance of a specific level of ground shaking over a given period. These motions are applied at the base of the considered soil profiles, and their vertical propagation is simulated using linear and nonlinear approaches in time or frequency domains. This paper provides a comprehensive literature review of the major input parameters for site response analyses, evaluates the efficiency of site response proxies, and discusses the significance of accurate modeling approaches for predicting bedrock motion amplification. The important dynamic soil parameters include shear-wave velocity, shear modulus reduction, and damping ratio curves, along with the selection and scaling of earthquake ground motions, the evaluation of site effects through site response proxies, and experimental and numerical analysis, all of which are described in this article.

This paper examines the effects of near-field pulse-like earthquake ground motions (GMs) on the seismic resilience, repair cost and time, and structural collapse risk of low-to-high-rise selected multi-story RC structures with special moment-resisting frames (SMRFs) and shear walls. Selected 5-, 10-, and 15-story structures are designed based on a seismically active region where pulse-like GMs are more likely to occur. Two different sets of near-field GMs are chosen based on the recommendations of FEMA P-695 to conduct nonlinear dynamic analyses. Subsequently, the methodology provided in FEMA P-58 is adopted to perform a comprehensive seismic performance assessment at various hazard levels. It is shown that the consideration of the effects of near-field pulse-like GMs can considerably increase the risk of structural collapse in RC shear wall systems, based on the ratio of the pulse period of ground motion records to the elastic first mode period, in comparison to the near-field GMs without a pulse. It is concluded that the stated ratio is a crucial parameter to assess the risk to the life safety (LS) of low-to-high-rise RC buildings. For frequently occurring seismic intensities, repairable damage to nonstructural elements is the main factor contributing to the total expected economic loss in the studied buildings, irrespective of the selected GM set and the number of stories. In addition, the contribution of collapse and demolition due to residual drift in the estimation of repair time is significant for pulse-like GMs.

This study addresses the critical need to understand the seismic behavior of cable-stayed bridges under Multi-Support Excitation (MSE) in order to mitigate earthquake-induced damage to these structures. The primary focus is on the investigation of response amplification phenomena and their seismic implications for cable-stayed bridges. Through a detailed comparative analysis of MSE and Synchronous Excitation (SE) across various structural locations, the study evaluates the impact of site-specific recorded ground motions of different earthquake categories. A pragmatic framework is developed to simulate realistic MSE ground motions for diverse earthquake scenarios, emphasizing the necessity of considering MSE in bridge design. The findings reveal a significant amplification of the design requirements due to antisymmetric mode excitation and increased tower and pier motions. The study also identified the need for in-depth analysis of cable-stayed bridges to address the increased vulnerability of tower-adjacent areas and to devise targeted reinforcement strategies of vulnerable components. These insights are critical for advancing seismic design practices and improving the resilience of cable-stayed bridges, contributing to safer urban infrastructure.

This paper aims to evaluate the failure probability of buried pipelines under pulse-like ground motions based on the seismic records detected during the Kahramanmaras, earthquake in Turkey. The incremental dynamic analysis (IDA) method was used to evaluate the vulnerability of continuous and segmented steel pipes, taking into account the corrosion effect in alkaline and near-neutral soil environments. The results show that pulse-like ground motion can significantly impact the fragility of buried pipelines, particularly segment steel pipelines. Moreover, the failure probability of buried pipelines tends to increase with service age, although the rate of failure gradually decreases. Empirical models notably underestimate the failure probability of buried pipelines under pulse-like ground motion, so they should be used cautiously in engineering application. These insights contribute to advancing our understanding of the seismic fragility of buried pipelines.

The objective of this study is to explore the seismic fragility of reinforced concrete bridges, specifically in response to the vertical components of ground motions, utilizing fragility surfaces. The examination of bridge responses involves the application of optimally selected intensity measures through three-dimensional nonlinear time-history analyses, encompassing uncertainties in both superstructure materials and soil-structure interaction effects. In this investigation, an extended Probabilistic Seismic Demand Model (e-PSDM) is employed, leveraging fragility surfaces to concurrently consider vertical and horizontal excitations. The results obtained from this approach are compared with traditional fragility curves. This study emphasizes Pile-cap displacement and drift ratio as pivotal engineering damage parameters, acknowledging their sensitivity to the influences of both soil-structure interaction effects and vertical ground motion. The fragility surfaces derived from the study reveal a correlation between increased vertical spectral accelerations and elevated probabilities of surpassing both slight damage and collapse limit states. These observations underscore the critical significance and practical utility of fragility surfaces in the context of performance-based seismic assessment and design for reinforced concrete bridges. The findings from this research contribute valuable insights into the nuanced behaviour of reinforced concrete bridges under seismic conditions, emphasizing the relevance of incorporating vertical components in fragility assessments for a more comprehensive understanding of structural vulnerability.

Strong ground shaking has the potential to generate significant dynamic strains in shallow materials such as soils and sediments, thereby inducing nonlinear site response resulting in changes in near-surface materials. The nonlinear behaviour of these materials can be characterized by an increase in wave attenuation and a decrease in the resonant frequency of the soil; these effects are attributed to increased material damping and decreased seismic wave propagation velocity, respectively. This study investigates the 'in-situ' seismic velocity changes and the predominant ground motion frequency evolution during the 2016 Kumamoto earthquake sequence. This sequence includes two foreshocks (M-w 6 and M-w 6.2) followed by a mainshock (M-w 7.2) that occurred 24 hr after the last foreshock. We present the results of the seismic velocity evolution during these earthquakes for seismological records collected by the KiK-net (32 stations) and K-NET (88 stations) networks between 2002 and 2020. We analyse the impulse response and autocorrelation functions to investigate the nonlinear response in near-surface materials. By comparing the results of the impulse response and autocorrelation functions, we observe that a nonlinear response occurs in near-surface materials. We then quantify the velocity reductions that occur before, during, and after the mainshock using both approaches. This allows us to estimate the 'in-situ' shear modulus reduction for different site classes based on V-S30 values (V-S30760 m s(-1)). We also establish the relationships between velocity changes, shear modulus reduction, variations in predominant ground motion frequencies and site characteristics (V-S30). The results of this analysis can be applied to site-specific ground motion modelling, site response analysis and the incorporation of nonlinear site terms into ground motion models.

Shallow sediments can respond non-linearly to large dynamic strains and undergo a subsequent healing phase as the material gradually recovers following the passing of seismic waves. This study focuses on the physical changes in the subsurface caused by the shaking from a buried chemical explosion detonated in a borehole in Nevada, USA, as a part of the Source Physics Experiment Phase II. The explosion damaged the shallow subsurface and modified the frequency content recorded by 491 geophones and 2240 Distributed Acoustic Sensing (DAS) channels within 2.5 km from surface ground zero. We observe a gradual shift of resonance frequencies in the 10-25 Hz frequency band in the hours following the explosion and develop a method to characterize the related logarithm-type healing process of the shallow (i.e., upper similar to 25 m) subsurface. We find that stronger levels of ground motion increase the relative degree of damage and duration of the subsurface healing; with the spall region exhibiting the largest degree of damage and longest healing recovery time. We observe coherent spatial patterns of damage with the region located to the southeast of the explosion exhibiting more damage than the southwest region. This study demonstrates that both DAS and co-located geophones capture similar temporal changes associated with the physical processes occurring in the subsurface, with the high-density sampling of DAS measurements enabling a new capability to monitor the fine-scale changes of the Earth's shallow subsurface following the detonation of a buried explosion. Strong seismic waves can damage the soft sediments that compose the shallow layers of the ground. A healing phase of the sediments generally follows the passing of the seismic waves as the medium gradually recovers with time. We study the spatio-temporal response of the subsurface in the vicinity of a large buried chemical explosion that was detonated in a borehole at the Nevada National Security Site, USA. The explosion, which was part of the Source Physics Experiment Phase II, was well instrumented along a surface fiber-optic cable with Distributed Acoustic Sensing (DAS) and hundreds of geophones. We find that the explosion, which generated a spallation of the shallow Earth, primarily damaged the upper similar to 25 m of the subsurface. We characterize the healing of the sediments and find a correlation between the duration of the healing phase and the level of maximum shaking. The high density of sensors also allows us to study spatial variations in the response of the shallow subsurface. This study demonstrates that both DAS and geophone continuous data similarly capture the spatio-temporal variations of the Earth's physical properties following strong ground motions, with DAS enabling meter-scale measurements of the subsurface changes. Shallow subsurface damage and subsequent healing caused by a buried chemical explosion are constrained with DAS and geophone data The explosion caused a relative drop of the average S-wave velocity in the Earth's shallow layers of a few percents The logarithm-type healing process of the subsurface exhibit a longer duration within the spall region