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High-speed railways are “lifeline projects” that shoulder the heavy responsibility of transporting relief supplies and medical forces for the first time after earthquakes. To ensure the train’s safety after earthquakes, it is of great urgency to ascertain a post-earthquake speed threshold. To that end, a target model for seismic irregularity emerges as a key parameter. In this paper, a null phase assumption-based technique for the mutual conversion between evolutionary power spectral density and non-stationary signal was proposed. Taking a high-speed railway track-bridge system as the research object, the target model of seismic irregularities was constructed based on the proposed technique. The rationality of the target model of seismic irregularities was verified, and the construction parameter settings were discussed. Moreover, a simplified frequency-domain fitting method for the target model of seismic irregularities was proposed based on the spectral decomposition theory. According to the research findings, the null phase assumption-based technique is capable of performing interconversion between seismic irregularity and its evolutionary power spectral density with satisfactory accuracy. It is recommended to set the minimum number of seismic irregularities, spatial sampling interval, hop size, and length of window function as 50, 0.25m, 1, and 40 to 100, respectively.

The present study deals with structural sensitivity of dynamic response having uncertainties in design parameters subjected to random earthquake loading. Earthquake is modeled as stationary random process defined by Kanai–Tajimi power spectral density. The uncertain design parameters are modeled as homogeneous Gaussian process and discretized through 3D local averaging. Subsequently the Cholesky decomposition of respective co-variance matrix is used to simulate random values of design parameters. The Neumann expansion blended with Monte Carlo simulation (NE-MCS) is explored for computing response sensitivity in frequency domain. Application examples related to a building frame and a gravity dam are presented serving to validate the NE-MCS technique in terms of its accuracy and effectiveness compared to direct Monte Carlo simulation and perturbation method.

Railway transportation, as an important lifeline during earthquake relief and post-disaster reconstruction, has an extremely significant role. The study of track irregularity caused by earthquakes is the basis for ensuring traffic safety after their occurrence. In this paper, a finite element model of a five-span simply supported high-speed railway beam bridge with the China Railway Track System (CRTS) II was established and an experimental verification was performed. Eighty arbitrarily selected seismic waves were extracted from the Pacific Earthquake Engineering Research Center (PEER) strong ground motion database and a nonlinear time-history analysis was performed on the finite element model. The frequency–domain distribution law of earthquake-induced track irregularities was studied. A stable target earthquake-induced track irregularity spectrum model was constructed, and its expression was fitted. According to the results, in the case of transverse earthquakes, the rails experienced noticeable alignment irregularity and cross-level irregularity, while the amplitude of the gauge and vertical irregularity were relatively small. The target irregularity spectrum has a higher amplitude in the low-frequency components. When peak ground acceleration (PGA) was low, earthquake-induced track irregularity was not obvious, but the deteriorating effects of earthquakes on track irregularities increased significantly with increasing PGA.

This study aims to investigate the adverse effects of near-fault ground motions on the long-term development of high-speed railways. In this paper, the ground motions are analyzed based on the Train–Track–Bridge Coupling Braking System (TTBCBS) which has been validated during earthquakes. The effects of earthquakes on the whole system are discussed in depth, focusing on the random nature of earthquakes, the impulsive character of near-fault earthquakes and the effects of different initial speeds on the system behavior. The results show that under random earthquakes, the probability of train derailment gradually increases with the increase of peak ground acceleration (PGA) of earthquakes. When the PGA exceeds 0.2g, the train is highly susceptible to derailment and the bridge itself may incur damage. When analyzing the nature of pulses of near-fault ground motions, it was found that the responses induced by class B and class C pulses are significantly similar. Meanwhile, the calculated values of derailment coefficients are basically the same when the PGA of class A pulse wave is at 0g and 0.1g. This suggests that train braking somewhat mitigates the response induced by near-fault ground motions. Furthermore, the value of improved spectral intensity (SI) for the running safety during earthquakes indicates that the increase in seismic intensity is detrimental to the system. In terms of the effect of train initial speeds on the system during earthquakes, it is observed that the system response reaches the lowest point when the train speed is 250km/h, which is more favorable to the smooth deceleration of the train. When the train speed is 400km/h, the system response reaches its maximum value. These research findings provide crucial insights and guidance for seismic safety design and management of high-speed railways.