Seismic safety of high concrete face rockfill dams (CFRD) on thick layered deposit is crucial. This study develops a seismic performance assessment procedure for high CFRD on thick layered deposit considering multiple engineering demand parameters (EDPs), and evaluates the effectiveness of gravel column and berm reinforcement for a typical CFRD. Solid-fluid coupled seismic response analysis of high CFRD on thick layered deposit is conducted using an advanced elasto-plastic constitutive model for soil, revealing the unique seismic response of the system, including the buildup of excess pore pressure within the thick deposit. Based on the high-fidelity simulations, appropriate intensity measure (IM) and EDPs are identified, and corresponding damage states (DS) are determined. Fragility curves are then developed using multiple stripe analysis, so that the probability of damage under different input motion intensities can be quantified for different DS. Using the proposed procedure, the reinforcement effects of berms and gravel columns are evaluated. Results show that berms can contribute significantly to reducing the probability of damage for the system, while the effect of gravel columns is unsatisfactory due to the limited achievable installation depth compared to the thickness of the deposit and low replacement ratio.

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.

Designers often assume a rigid foundation for buildings in seismic zones, believing it ensures safety during earthquakes. However, this assumption may neglect important factors, such as soil-structure interaction (SSI) and the potential for collisions between adjacent buildings. This study investigates the effect of dynamic SSI on the seismic pounding response of adjacent buildings. A nonlinear finite-element analysis was performed on three cases: bare buildings, buildings with linear fluid viscous dampers (LFVDs), and buildings with nonlinear fluid viscous dampers (NFVDs). The dynamic contact technique, in which contact surfaces with both the contactor and target, was employed to mimic the mutual pounding. Key seismic response parameters, including acceleration, displacement, inter-story drift, and pounding forces, were analyzed. The results showed that dynamic SSI significantly affects the seismic performance of adjacent buildings, altering the number, timing, and intensity of collisions. In some cases, SSI increased inter-story drifts beyond code-permissible limits, indicating that relying on a rigid foundation assumption could lead to unsafe structural designs. Additionally, SSI had a notable impact on the forces in NFVDs, highlighting the need for careful design considerations when using these devices. The study further investigates the effect of soil flexibility on the performance of nearby structures under different seismic excitations, focusing on the NFVDs case with a 10 % damping ratio. Incremental Dynamic Analysis (IDA) and fragility analysis were conducted to assess performance under seismic excitations, focusing on three performance levels: Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP). While SSI had minimal impact on the more flexible buildings, it significantly affected the more rigid building, particularly at LS and CP levels, making it more vulnerable to damage compared to buildings on rigid foundations. These findings underscore the importance of incorporating SSI in seismic design to ensure structural safety.

As an important coastal protective structure, the breakwater is prone to failure due to foundation damage under seismic actions. However, the seismic performance evaluation of breakwaters has received little attention. This study conducts a seismic fragility analysis of composite breakwaters constructed on liquefiable foundations. By adopting a performance-based seismic design (PBSD) approach and considering the record-to-record (RTR) variability of ground motions, the seismic performance of the breakwaters is assessed over their entire lifecycle. Based on the results of the parameter sensitivity analysis, the reinforcement schemes were proposed in terms of delaying foundation liquefaction and limiting the lateral displacement of liquefied soil. The results of the seismic intensity measure (IM) parameter selection indicate that the commonly used peak ground acceleration (PGA) exhibits a weak correlation with the seismic response of the breakwater, whereas the cumulative absolute velocity (CAV) has a strong correlation. The comparison of the reinforcement schemes shows that the Dense Sand Column (DC) scheme provides significant reinforcement effects, while the Concrete Sheet Pile (CSP) scheme is more suitable for reinforcing existing breakwaters. The seismic performance assessment framework can also be applied to other structures where structural damage is closely related to foundation deformation, such as caisson quays and embankments.

The wind resistance of transmission towers is not only affected by wind load, but also by service environment. This study uses the world's second Ultra High Voltage Direct Current transmission project - Xinjiang & PLUSMN;800 kV Tianzhong Line UHV DC transmission project - to develop a fragility analysis method for transmission towers in saline soil under wind loads to investigate the change of wind loads fragility of transmission towers in long-term service in the saline soil environment. It develops a tower-line-foundation (3 T-2L-F) system model considering soil-structure interaction. In addition, this research addresses the durability damage of the transmission tower using field investigation data and material degradation models and analyzes the influence of various durability damage components on the natural vibration mode of the basic of 3 T-2L-F model. Finally, it builds the structure-wind samples utilizing a Latin hypercube sampling method and explores the time histories analysis, the pushover analyses, and the time-varying fragility analyses considering the uncertainty of materials and wind loads. The findings indicate that the 3 T-2L-F model accurately simulates the actual situation of the transmission tower. The fragility of a transmission tower subjected to wind loads is proportional to the degree of material damage and the strength of wind loads.

API-RP2EQ (2021) has recommended annual probabilities of failure for Jacket-Type Offshore Platforms (JTOPs) against earthquake events and has specified that catastrophic failure modes that can lead to environmental damage or loss of structural integrity shall not occur during an Abnormal Level Earthquake (ALE). In this study some structural and non-structural limit states are proposed for the seismic evaluation of JTOPs and a comprehensive methodology is used for evaluating the probabilities of reaching relevant limit states, considering the nonlinear dynamic behavior of JTOPs, soil-pile interaction, pipeline risers, and relevant uncertainties. Incremental Dynamic Analysis (IDA) has been carried out on finite element models of platforms, and record-to- record and epistemic uncertainties have been considered in deriving fragility curves. Results show that the slope-based limit states derived from nonlinear static pushover curves provide a fairly good estimate of the target annual probability of structural failure. They also show that a non-structural limit state associated with containment leakage of pipeline risers should also be considered in the analysis. The research provides valuable insights into probabilistic performance-based seismic assessment of steel jacket-type offshore platforms and indicates that the reserve strength coefficients recommended in the relevant standard may be too conservative.

Seismic risk assessment is pivotal for ensuring the reliability of prefabricated subway stations, where selecting optimal intensity measures (IMs) critically enhances probabilistic seismic demand models and fragility analysis. While peak ground acceleration (PGA) is widely adopted for above-ground structures, its suitability for underground systems remains debated due to distinct dynamic behaviors. This study identifies the most appropriate IMs for soft soil-embedded prefabricated subway stations at varying depths through nonlinear finite element modeling and develops corresponding fragility curves. A soil-structure interaction model was developed to systematically compare seismic responses of shallow-buried, medium-buried, and deep-buried stations under diverse intensities. Incremental dynamic analysis was employed to construct probabilistic demand models, while candidate IMs (PGA, PGV, and vrms) were evaluated using a multi-criteria framework assessing correlation, efficiency, practicality, and proficiency. The results demonstrate that burial depth significantly influences IM selection: PGA performs optimally for shallow depths, peak ground velocity (PGV) excels for medium depths, and root mean square velocity (vrms) proves most effective for deep-buried stations. Based on these optimized IMs, seismic fragility curves were generated, quantifying damage probability characteristics across burial conditions. The study provides a transferable IM selection methodology, advancing seismic risk assessment accuracy for prefabricated underground infrastructure. Through a systematic investigation of the correlation between IM applicability and burial depth, coupled with the development of fragility relationships, this study establishes a robust technical framework for enhancing the seismic performance of subway stations, and provides valuable insights for seismic risk assessment methodologies in underground infrastructure systems.

Probability-based seismic fragility analysis provides a quantitative evaluation of the seismic performance exhibited by structures. This study introduces a framework to perform seismic fragility analysis of utility tunnel and internal pipeline system considering wave passage effect of the ground motion spatial variation. The numerical model of a double-beam system resting on a nonlinear foundation is established to simulate the soiltunnel-pipeline interactions. 17 pairs of earthquake records are chosen and scaled as inputs at the outcrop. One-dimensional (1D) free-field analyses are conducted to obtain the ground motion time histories at the bottom slab of the utility tunnel, and then incremental dynamic analysis (IDA) is performed for the utility tunnel-internal pipeline system. The damage states (DSs) are defined by the maximum joint opening for the utility tunnel and maximum strain for the internal pipeline, and the peak bedrock velocity (PBV) is determined to be the most representative intensity measure (IM) for developing the seismic fragility curves. The seismic fragility curves of the system are constructed using the joint probabilistic seismic demand model (JPSDM) and Monte Carlo sampling method. The research findings indicate that: (1) the framework proposed in this study is suitable for the fragility assessment of long-extended utility tunnel-internal pipeline system; (2) the utility tunnel and internal pipeline as a system exhibit greater fragility compared to either one of the components, and the JPSDM and Monte Carlo sampling method for the system fragility analysis is more precise than the first-order bound method; (3) the proposed fragility curves in this study provide quantitative damage probabilities for the individual components and system under different seismic intensity levels. (4) The IM values corresponding to 50% exceedance failure probability of the whole system is 1%-3% lager than that of the upper bounds, and it is 3% to 5% less than that of the lower bounds. The conservative upper bound is a more suitable approximation for system fragility. (5) It should be noted that the obtained fragility curves are valid for the considered tunnel-pipeline structure and site conditions. For different tunnel structures and site conditions, the fragility curves can be constructed following the same steps outlined in this study.

Ensuring the structural resilience of shield tunnels is critical in seismically active regions. Liquefaction induced by seismic activity poses an additional hazard to tunnel safety. The study performed seismic fragility analysis using the incremental dynamic analysis method which utilized a finite element model of a saturated porous seabed shield tunnel. The findings highlighted that different liquefaction mechanisms are observed in different types of the soil surrounding the tunnel. The thickness of the fine sand layer (FSL) surrounding the tunnel significantly affects seabed liquefaction depth and the tunnel's maximum bending moment (Mmax). The highest Mmax and damage probabilities were observed when the tunnel was entirely embedded in the FSL, whereas the smallest Mmax and lowest damage probabilities occurred when the tunnel was partially within the sand and clay. This study could also provide some insights on seismic mitigation strategies in subsea shield tunnels and the soil type influences the timing of Mmax occurrence and emphasized the critical role of seismic frequency in determining the tunnel's response.

The current Indian Standard Seismic Code IS 1893: Part 1 (2016) for general buildings lacks detailed guidelines on modeling soil-structure interaction (SSI) in the estimation of seismic demand and earthquake-induced damage in reinforced concrete buildings. Therefore, this study aims to investigate the effects of SSI, with a focus on its nonlinear behavior, on the seismic demand of ductile reinforced concrete frames designed as per IS 1893: Part 1. The selected RC buildings are designed for second-highest seismic risk zone in India and represent short, medium, and long-period structures commonly found across Indian sub-continent. The influence of SSI is studied for soil type II and type III, as specified in the Indian Code, which corresponds to medium stiff and soft soil sites, respectively. Using a nonlinear Winkler-based model, numerical finite element models of linear and nonlinear SSI have been developed for isolated shallow foundations. This study utilizes the results of incremental dynamic analysis to evaluate the fragility parameters for code specified performance limit states. Further, the estimated fragility parameters are integrated with the regional hazard curve coefficients to quantify the annual exceedance probability of specified damage levels. The simulation results highlight the critical impact of nonlinear SSI on the earthquake resilience of IS code designed low- to high-rise reinforced concrete buildings. Notably, the percentage increase in estimated fragilities is higher for low-rise buildings than high-rise buildings when subjected to ground motions on soil sites. Additionally, the vulnerability to failure of these buildings elevates significantly when they are analyzed on soft soil sites compared to medium soil and bedrock sites. Therefore, it is recommended to account for the significance of nonlinear SSI while assessing the expected structural performance and fragility of IS 1893: Part 1 designed stiff low- to medium-rise reinforced concrete buildings, as this step can substantially enhance the resiliency of such buildings in the aftermath of a disastrous earthquake.