This paper investigated the influence of chloride ion erosion and aftershocks on the seismic performance of transmission tower structures in Xinjiang, China. Based on chloride ion diffusion laws and steel corrosion mechanisms, the time-dependent deterioration of reinforced concrete was analyzed. Finite element models considering corrosion effects were established for different ages(0a,50a,70a,100a) in a saline soil environment using ANSYS/LS-DYNA. Ten mainshock-aftershock sequences tailored to the site type was constructed, and the cumulative damage index (DI) was adopted as a metric for structural damage. The results indicate that aftershocks and steel corrosion significantly impact transmission tower damage, with damage extent influenced by the intensity of the main shock. Stronger aftershocks cause greater additional damage, potentially exceeding 50 % cumulative damage when their amplitude matches the main shock. Steel corrosion alone can lead to nearly 40 % damage. Its influence on seismic fragility varies with damage state, especially under moderate to complete damage, where longer service life increases vulnerability. The coupling of corrosion and aftershocks further elevates structural vulnerability. Hence, in seismic assessments of transmission towers in saline soil environments, combined effects of main and aftershocks, and corrosion, must be accounted for.

Antislide piles are currently applied widely in slope reinforcement engineering, but investigation of the stability of slopes stabilized with this measure under the action of mainshock-aftershock (Ms-As) sequences is very limited. In this study, the probability density evolution method (PDEM) and the Newmark method is adopted to evaluate the reliability of slope reinforced by antislide piles subjected to Ms-As sequences considering the spatial variability of material parameters. Firstly, stochastic Ms-As sequences are generated by combining a physical function model, the Copula function, and the narrowband harmonic group superposition method. In addition, the spectral representation method is taken to generate the random field and the parameters are assigned to the numerical model. Then, the Newmark method is applied to batch-calculate the permanent displacement (Disp) of the slope caused by the Ms-As sequences. The effects of pile position, pile length, and coefficient of variation of cohesion and friction angle (COVC and COVF) on the average value of Disp are discussed. Finally, based on the PDEM, the seismic reliability of the slope strengthened by antislide piles subjected to the Ms-As sequences are obtained. The research results indicate that with the COV increases, the average value of Disp of the slope shows a gradual tendency to increase, and the average value is more sensitive to COVC. Compared with the unreinforced slope, the Disp of the slope strengthened by antislide piles is reduced. The cumulative damage caused by the aftershock and the risk of failure can be significantly reduced by setting a reasonable antislide pile.

To date, numerous coral sand revetment breakwaters have been constructed in oceanic regions to resist wave impact and scour. However, frequent earthquakes significantly threaten their stability, especially during mainshock-aftershock sequences, where aftershocks can further exacerbate the risk of damage or collapse. This study proposes a reinforcing countermeasure, i.e., geosynthetics reinforced soil technique, to mitigate seismic deformation and enhance the resilience of revetment breakwaters against earthquakes. A series of shaking table tests were conducted on coral sand revetment breakwaters to examine the effect of geogrid reinforcement on their seismic performance under mainshock-aftershock sequences. Additionally, the reinforcement mechanism of geogrid was elucidated through supplementary cyclic triaxial tests. The results indicate that acceleration amplification intensifies during aftershocks, while geogrid reinforcement mitigates this detrimental effect. The inclusion of geogrid also decreases the buildup of excess pore water pressure (EPWP) under mainshockaftershock sequences. Coral sand shear dilation results in the generation of notable negative EPWP within revetment breakwaters, and more significant negative EPWP oscillation, compared to the aftershocks, is observed in the mainshock. Additionally, geogrid decreases the maximum cumulative settlement in reinforced revetment breakwaters by over 54 % compared to unreinforced structures. The cumulative damage induced by aftershocks exacerbates the damage to coral sand revetment breakwaters, leading to the emergence and rapid progression of lateral displacements. Nevertheless, geogrid reinforcement mitigates this adverse effect and prevents the formation of plastic slip planes, thereby altering the deformation pattern of the revetment breakwater subjected to mainshock-aftershock sequences. Overall, geogrid reinforcement is found to be highly effective in enhancing the stability of coral sand revetment breakwaters against mainshock-aftershock sequences and holds promising applications in infrastructure construction in coral sand island and reef areas.

Pipelines are important structural elements that are frequently used today to meet many infrastructures needs such as drainage, natural gas or water transmission. In this context, the usability of such structures, which are important elements of infrastructure systems, especially after disasters such as earthquakes, is of great importance. For this reason, within the scope of this study, a parametric investigation of the seismic behaviors of a natural gas pipeline system under mainshock-aftershock sequences have been carried out, specifically taking into account the soil-natural gas pipeline interaction (SNGPI) in the help of finite element model (FEM) proposed. Before developing the model of SNGPI system proposed using solid element, the fundamental mode frequencies of the pipeline system modeled using the solid element for the verification have been compared with those of obtained from the pipeline system modeled using the beam element and the analytical solutions. After verification of proposed model is demonstrated, SNGPI system has been modeled and its fundamental modes have been compared with mode frequencies of soil stratum obtained from well-known simple analytic solutions. After this stage, the dynamic analyses of natural gas pipeline (NGP) system in the time domain have been carried out using four different soil systems and four different mainshock-aftershock sequences. The results of the nonlinear time-history analyses have been investigated in terms of the stress and the displacement responses. Parametric evaluations show that the greatest displacements and the stresses occurring at the considered nodes of NGP system may be importantly affected from mainshock-aftershock sequences and soil stiffness changes. As the soil stiffness decreases, both the peak stresses and displacements increased significantly. On the other hand, the same responses obtained under mainshock loadings, which have relatively lower peak ground acceleration (PGA)/ peak ground velocity (PGV) ratio compared to aftershock loadings, are generally larger than those obtained under aftershock loadings.

Aftershocks frequently induce further damage to slopes that have already been compromised by mainshocks. Most of the current research concentrates on the case-based studies of structural response to the mainshock-aftershock sequences (MAS), however, the influence of the MAS parameter characteristics has not been adequately considered. In this study, the peak characteristic, spectrum characteristic, cumulative characteristic and polarity effect of the MAS were considered, the correlation between 21 MAS parameters and slope response were analyzed, and the response characteristics of soil slope under the MAS action were comprehensively and systematically revealed. The results show that: (1) Aftershocks can induce significant incremental damage to slopes, with the extent of this damage being contingent upon the severity of damage caused by the mainshock; (2) Among the MAS parameters, the Cumulative Absolute Velocity (CAV(ma)) and Peak Ground Velocity (PGV(ma)) are optimal for assessing the response of soil slopes under MAS conditions. Furthermore, the incremental damage caused by aftershocks can be predicted using the displacement increment ratio (delta(D)); (3) The polarity of the MAS has an impact on the displacement of the slope, following the pattern: MAS along-slope direction > mainshock along-slope direction and aftershock reverse-slope direction > aftershock along-slope direction and mainshock reverse-slope direction > MAS reverse-slope direction; (4) The MAS polarity also affects the correlation between the MAS parameters and the slope displacement response, especially for the aftershock displacement. The research results aim to provide a foundation for the selection of evaluation factors and the analysis of soil slopes stability under the MAS action.

Most existing seismic behavior analyses of underground structures simply consider a single earthquake. Meanwhile, the diaphragm wall, as an enclosure structure, is regarded as a security reserve and is always ignored in current studies. Herein, the characteristics of a diaphragm wall-subway station system with different connection modes under earthquake sequences were investigated using numerical simulation. The damage degree of the structural component was calculated through quantitative analysis of the tensile damage picture. The seismic damage level of the station structure was evaluated to characterize the damage transition effect induced by the aftershock according to the inter-story drift angle. Moreover, an empirical model for predicting the inter-story drift angle with respect to different peak accelerations was proposed. The research results indicate that the effect of the connection mode between the sidewall and the diaphragm wall on the damage evolution and deformation behavior of the station structure is significant. Compared with that of the compound wall structure, the seismic damage to the sidewall of the composite wall structure is much less severe, but the slabs become more vulnerable and suffer more severe damage. The accumulative damage triggered by aftershocks aggravates the extent of structural damage and even leads to damage transition. The conclusions illustrated in this paper contribute to a better understanding of the seismic resistance design of diaphragm wall-subway station systems under earthquake sequences.

A series of centrifuge model experiments were performed in this study to investigate the sand reliquefaction behavior in free field and pile group models subjected to repeated shakings. Toyoura sand was used to prepare the model ground with 50 % relative density and experimented at 50g centrifugal acceleration. A 2 x 2 pile group model was used to examine the response of piles and its effect on sand reliquefaction during repeated shakings. A seismic sequence comprising foreshocks-mainshock-aftershocks-mainshock pattern was imparted to both free field and pile group models. In addition, an independent mainshock was imparted to a free field model and compared with the seismic sequence to examine the effect of foreshocks in triggering future liquefaction. Acceleration time response, excess pore pressure (EPP), ground subsidence, bending moment and lateral displacement of the pile group were measured. Significant de-amplification and unsymmetrical response with presence of shear-induced dilatancy spikes were observed in both free field and pile group models. Results from this study indicate that foreshocks and aftershocks are not sufficient to induce liquefaction. However, liquefaction and subsequent reliquefaction were recorded in both models during mainshocks. Pile group recorded smaller EPP response and subsidence compared to free field model. Higher magnitude of reliquefaction was induced even at moderate depths during the second mainshock at a quicker time. This was primarily associated with the increase in magnitude of anisotropy due to repeated generation and dissipation of pore water which results in decrease in resistance to further reliquefaction. Hardening induced around the vicinity of the pile group due to sand densification has resulted in smaller bending moment values during second mainshock compared to the first.

Seismic records are composed of mainshock and a series of aftershocks which often result in the incremental damage to underground structures and bring great challenges to the rescue of post-disaster and the repair of post-earthquake. In this paper, the repetition method was used to construct the mainshock-aftershocks sequence which was used as the input ground motion for the analysis of dynamic time history. Based on the Daikai station, the two-dimensional finite element model of soilstation was established to explore the failure process of station under different seismic precautionary intensities, and the concept of incremental damage of station was introduced to quantitatively analyze the damage condition of structure under the action of mainshock and two aftershocks. An arc rubber bearing was proposed for the shock absorption. With the arc rubber bearing, the mode of the traditional column end connection was changed from fixed connection to hinged joint, and the ductility of the structure was significantly improved. The results show that the damage condition of the subway station is closely related to the magnitude of the mainshock. When the magnitude of the mainshock is low, the incremental damage to the structure caused by the subsequent aftershocks is little. When the magnitude of the mainshock is high, the subsequent aftershocks will cause serious incremental damage to the structure, and may even lead to the collapse of the station. The arc rubber bearing can reduce the damage to the station. The results can offer a reference for the seismic design of subway stations under the action of mainshockaftershocks.

During the 1995 Kobe earthquake, the Daikai Station suffered a severe collapse, drawing more attention to the earthquake damage response of underground structures. However, the performance of underground structures under the mainshock-aftershock sequences has yet to receive much attention. In this paper, the dynamic response and damage development process of the subway station under the mainshock-aftershock sequence were studied and explored through a series of centrifuge shaking table tests. The Selection-Adjustment-Generation method of artificial main aftershock sequence construction was introduced. Steel grits were mixed into the overlying soil to simulate the vertical inertia force. It is found that the Selection-Adjustment-Generation method is easily implemented, maintaining the local time-frequency characteristics of the original seismic waves as much as possible. The failure mechanism of the subway station subjected to mainshock-aftershock sequences can be summarized into two main aspects. One is the reduction of the horizontal deformation capacity of the columns due to the vertical inertial force induced by the overlying soil under the vertical seismic load. Sudden brittle failure will happen to the columns with higher axial pressure under horizontal earthquakes, which weakens their vertical support capacity. The other is the damage accumulation under mainshock-aftershock sequences. The station in the dry sand site is more susceptible to damage for the amplification effect. Both ends of the columns of the subway station experience crack with a strain exceeding 500 mu epsilon during the mainshock. During the second aftershock, the bottom of the outer columns was crushed. In the liquefiable site, the liquefied layer weakens the upward propagation of horizontal seismic load and protects the structure to a certain extent. This series of tests illustrate the damage development process of underground structures under the main-aftershock and provides valuable experimental data for further study of the earthquake damage response of underground structures.

This research presents an efficient computational method for retrofitting of buildings by employing an active learning-based ensemble machine learning (AL-Ensemble ML) approach developed in OpenSees, Python and MATLAB. The results of the study shows that the AL-Ensemble ML model provides the most accurate estimations of interstory drift (ID) and residual interstory drift (RID) for steel structures using a dataset of 2-, to 9-story steel structures considering four soil type effects. To prepare the dataset, 3584 incremental dynamic analysis (IDA) were performed on 64 structures. The research employs 6-, and 8-story structures to validate the AL-Ensemble ML model's effectiveness, showing it achieves the highest accuracy among conventional ML models, with an R-2 of 98.4%. Specifically, it accurately predicts the RID of floor levels in a 6-story structure with an accuracy exceeding 96.6%. Additionally, the programming code identifies the specific damaged floor level in a building, facilitating targeted local retrofitting instead of retrofitting the entire structure promising a reduction in retrofitting costs while enhancing prediction accuracy.