Xiaolei Wang

Given that vector-valued ground motion intensity measures (IMs) have been the focus in recent research, conditional probabilistic seismic hazard analysis (PSHA), conditional return period, and conditional site-spectra have consequently garnered more attention. The proposed methods primarily focus on horizontal ground motion, which have been shown to be valuable in the seismic hazard assessment for engineering structures and the selection of seismic ground motion. However, the potential hazard of vertical ground motion should be considered in the analytical process. Additionally, considering the spatially and temporally inhomogeneous characteristics of seismicity in China, the application of the aforementioned methods to Chinese sites requires more refined development. For the aforementioned purpose, in this paper, with the horizontal intensity measure as the primary intensity measure and the vertical intensity measure as the secondary intensity measure, the theory of vertical conditional PSHA, vertical conditional return period and vertical conditional site-specific spectra are summarized and applied to Chinese sites. To enable the Chinese conditional PSHA (c-CPSHA) method to be implemented more efficiently and precisely, the procedure of c-CPSHA was provided based on the Monte Carlo simulation (MCS) method. For the case study site, the vertical conditional PSHA was conducted. Both the results of vertical conditional PSHA and vertical conditional return period were generated. These results were applied to the generation of vertical conditional uniform hazard spectra. It was found that vertical conditional PSHA curves and vertical conditional return period curves show different results for various combinations of intensity measures, which typically related to the correlation coefficient between primary intensity measure and secondary intensity measure and the hazard level of the primary intensity measures. The generated vertical conditional uniform hazard spectra is more reasonable compared to vertical uniform hazard spectra and vertical conditional mean spectra. These findings can be developed conditional hazard maps and ground motion selection of horizontal and vertical ground motions to perform nonlinear time-history dynamic analysis of structures in China.

Previous studies have found that focusing solely on the effects of horizontal mainshock ground motions can hardly meet the demands of modern seismic design, as vertical ground motions have exhibited significant destructive potential. Meanwhile, the continuous effect of aftershocks can further exacerbate structural damage, showing a typical phenomenon of damage accumulation. Therefore, it is necessary to conduct a detailed analysis of the influence of three-dimensional mainshock - aftershock ground motions on the seismic performance of engineering structures. In this paper, three concepts of multivariate return periods for three-dimensional mainshock - aftershock ground motions are proposed, and the assumption that the intensity measures of such ground motions follow a multivariate log - normal distribution is validated. Based on this theoretical foundation, a multivariate Gaussian mixture model for three-dimensional mainshock - aftershock ground motions based on the multivariate return period is established to select such ground motions. Applying the selected ground motion records to a case study of a tunnel structure, it can be observed that vertical ground motion expands the plastic deformation of the tunnel soil and the damage of the lining toward the invert and crown, while the additional effect of aftershocks further intensifies both the plastic deformation of the soil and the damage of the lining. Meanwhile, as the mainshock - aftershock peak acceleration ratio increases, the damage ratio of the tunnel lining structure exhibits a nonlinear increasing trend.

1. Freeze–thaw degradation of tunnel linings in cold regions poses a critical threat to structural safety and operational reliability. Statistical surveys have shown that over 65% of existing tunne...

Tunnels traversing strata with water-rich karst and coal seam goafs face prominent risks of multi-field coupling disasters. However, systematic experimental data and high-precision prediction methods for lining internal force responses under such coupled conditions remain scarce. This study, based on the Changliangzi Tunnel in China, conducted seven sets of 1:50 scale physical model tests covering gravity-only, water-rich karst, goaf and multi-field coupling conditions. An experimentally validated FLAC3D model was established. To overcome the limitation of small samples, the Auxiliary Classifier Generative Adversarial Network (ACGAN) was introduced for data augmentation. The prediction model was developed integrating physical model tests, numerical simulation, generative adversarial network-based data augmentation and explainable machine learning. The research results indicate that in the experimental simulations, water-rich karst and goafs lead to internal force redistribution and asymmetric deformation; through multi-parameter combinations, 50 numerical simulation cases were expanded, and data augmentation generated 800 high-quality synthetic samples, constructing a fused dataset containing 857 samples; The GA-LightGBM prediction model achieved an average coefficient of determination (R²) of 0.9057 on the test set, outperforming comparative models such as XGBoost, CatBoost and deep neural networks in both accuracy and efficiency; The SHAP framework was employed to quantitatively reveal the contribution mechanism of disaster-causing factors with tunnel depth as the globally dominant factor, followed by goaf thickness, karst location, distance to goaf, karst water pressure and secondary lining elastic modulus, which exhibits a "global dominance with local targeting" characteristic, wherein tunnel depth establishes the baseline structural stress level, while goaf and karst parameters significantly intensify local internal force concentration and damage risk at specific locations through local effects. The developed prediction model can provide a basis for intelligent design and risk assessment of tunnels under complex geological conditions.

In the seismic analysis of structures and structural safety assessment, the joint occurrence of horizontal and vertical ground motions should be considered. In this paper, based on the joint distribution of horizontal and vertical generalized intensity measures, the theory of vector generalized conditional intensity measure (VGCIM) are summarized, and the theories of simultaneous exceedance, arbitrary exceedance and Kendall-based multivariate return periods (MRPHV,K) are proposed, which are subsequently applied to a case study site analysis. For the case study site, the results show that when calculating the target IMHV multivariate return period using the conditions IM and GCIM, the return period calculated via the Kendall-based method most closely matches the target return period; The joint MRPHV,K of intensity measures in VGCIM is more closely matched to the target return period than the joint MRPHV,K of intensity measures in GCIM and GCIM-avg; The hazard of multiple intensity measures can be assessed using the joint MRPK value from two intensity measures; When comparing different ground motion selection methods, the target spectral generated using the VGCIM-based, GCIM-avg-based and Kendall multivariate return period selection methods would present a relatively moderate mean and standard deviation; Furthermore, the VGCIM-based, GCIM-avg-based and Kendall multivariate return period selection methods show lower sensitivity to the selection of conditional seismic motion models, which indicate these methods are more reasonable ground motion selection method.

This study proposes a spatiotemporal reliability analysis framework for tunnel linings to evaluate their long-term safety in cold karst environments, where structures are subjected to coupled geological and freeze-thaw actions. The methodology systematically integrates the spatial randomness of geology with the temporal degradation of materials. It introduces a total probability analysis to encompass the complete influence chain: from geological uncertainty to induced mechanical response, to subsequent stress-accelerated material degradation, and ultimately to the time-dependent evolution of failure probability. The proposed approach comprises three main components. First, a probabilistic model of the karst cave radius is established on the basis of field borehole data via a negative exponential distribution. The geological uncertainty is then propagated to the probability distribution of the lining stress ratio η via a random variable transformation method. Second, a stress ratio‐regulated Gamma process model for concrete strength degradation under freeze‐thaw cycles is constructed, revealing the nonlinear regulatory effect of the stress state on the material degradation rate. Accordingly, a three-dimensional response surface relating time, stress ratio, and strength degradation is developed. Finally, the stress ratio distribution and conditional failure probability are coupled via the total probability formula to derive the time-varying marginal failure probability curve of the lining, which explicitly accounts for geological randomness. A case study of a karst tunnel along the Benxi–Huanren Expressway in Liaoning Province, China, is conducted to validate the framework. The results demonstrate that neglecting the spatial randomness of karst caves may lead to overestimation or underestimation of the lining service life. The proposed method provides a theoretical foundation for the durability design and operation‐maintenance decision‐making of karst tunnels in cold regions. This study offers a systematic and quantifiable analytical tool for the reliability assessment of tunnel linings under the coupling effect of multiple factors.

This paper examines the empirical correlations between 14 intensity measures (IMs) describing the frequency content, amplitude, cumulative effects, and duration aspects of ground motion based on the NGA‐West2 database. The correlation results in this paper are compared with the results of previous models based on the NGA‐West1 database, and the previous correlation coefficient models are updated and extended. The comparison results show that the trend of the correlation coefficients of the model established in this paper is essentially consistent with previous models based on the NGA‐West1 database, with most correlation coefficients observed in this paper being slightly lower than in previous studies. In addition, this paper extends the generalized conditional intensity measure (GCIM) ground motion selection method so that it can consider multiple conditional IMs (VGCIM), and gives full theoretical details. The differences between the theories of VGCIM and GCIM are discussed, and several possible application scenarios of VGCIM are illustrated. An example application of VGCIM is shown, and the results show that there are deviations between the target IMs conditional distribution constructed after considering multiple conditional IMs and considering one IM that is sufficient to make an impact in the ground motion selection. Finally, the effect of the correlation coefficient model on the IMs conditional distributions generated based on GCIM and VGCIM is discussed.

Precast segmental reinforced concrete (RC) piers have been widely used in the construction of offshore bridges to speed up construction. Offshore bridges in cold regions are inevitably affected by the seawater freeze–thaw cycles under the periodic movement of tides, which could reduce the mechanical property of RC piers. Based on the low cyclic loading test on 12 specimens with different seawater freeze–thaw cycles, axial compression ratio, diameters of longitudinal reinforcement, and stirrup spacing, the hysteresis characteristics of precast segmental RC piers were analyzed. The test results show that the peak load decreased by 11%, while the peak displacement increased by 40% after 125 seawater freeze–thaw cycles. The hysteresis curves became fuller and the residual displacement became smaller with the accumulation of freeze–thaw damage. In the same 125 freeze–thaw cycles, the peak load increased by 15% and 27% while increasing the axial compression ratio and the longitudinal reinforcement diameter. Combined with the regression analysis of the experimental results, the restoring force model of RC piers considering the seawater freeze–thaw damage and design parameters was established, and the calculation method of each characteristic point in the model was given. The deviation values of flexural capacity are not more than 6.5%, and the deviation values of peak displacement are not more than 12%. The restoring force model determined in this paper could provide a reference for seismic response analysis of offshore bridges in cold regions.