Effects Of Ground Motions Research Articles

Effect of Pulse-like Ground Motions with Various Pulse Indicators on the Seismic Fragility of Bridges

Effect of Pulse-like Ground Motions with Various Pulse Indicators on the Seismic Fragility of Bridges

Seismic fragility assessment of eccentric gravity column-core tube structures subjected to pulse-like ground motions

The effects of pulse-like ground motion and structural eccentricity on the seismic fragility and anti-collapse behavior of the new gravity column-core tube structural system are investigated. Numerical models of the gravity column-core tube structure are first established employing the CANNY program and validated against the shaking table test results. Subsequently, reference symmetric gravity column-core tube structures with 10-, 20- and 30-stories are designed, and then their eccentric structures are established by changing the nodal mass distribution. Ten pulse-like and ten corresponding non-pulse-like ground motion records are selected as the seismic excitations. The seismic fragility and anti-collapse analysis of these eccentric structures are conducted. The results show that the pulse-like ground motion significantly affects the seismic response and fragility of the gravity column-core tube structures, with an apparently higher probability of exceeding the limit states (Pf) for the pulse cases than those for the non-pulse cases. With increasing eccentricity, the Pf shows an increasing trend. Besides, both the pulse-like ground motion and the increase of eccentricity lead to a decline in structural anti-collapse capacity. The results are expected to provide a reference for the seismic design of the new gravity column-core tube structures.

Unified framework for stochastic dynamic responses and system reliability analysis of long-span cable-stayed bridges under near-fault ground motions

Long-span cable-stayed bridges are complex systems with numerous components, and prone to failures of multiple components under near-fault ground motions with long-period velocity pulses. The evaluation of dynamic system reliability of cable-stayed bridges is an important challenging issue. In this work, a unified framework for simultaneously determining both the stochastic dynamic responses and system reliabilities of long-span cable-stayed bridges under near-fault stochastic ground motions is proposed based on direct probability integral method (DPIM) with adaptive strategy. Firstly, the 3-dimensional finite element model of typical cable-stayed bridge and the stochastic synthesis model of near-fault ground motions are established. Based on probability density integral equation, new formulas in input probability space of time-variant moments of response are derived. Then, DPIM with adaptive strategy is suggested to calculate the mean value and standard deviation of response via new formulas. Dynamic system reliability of cable-stayed bridge under near-fault stochastic ground motions is evaluated by establishing failure criteria of extreme value mappings of multiple performance functions. Finally, numerical results indicate that the long-period velocity pulse of near-fault motions imposes an important effect, resulting in large mean responses and failure of cables. Failure probability of cables is significantly increased with the occurrence of velocity pulses, which causes the decrease of system reliability of cable-stayed bridge. Thus, the randomness and velocity pulse effect of near-fault ground motions should be seriously considered for reliability-based design and safety assessment of cable-stayed bridges.

Pulse component extraction and its application in simulation of pulse-like ground motions

A procedure for simulating new pulse-like ground motion based on natural pulse-like ground motion record is proposed. Firstly, an extraction method of pulse waveform based on Modified Ensemble Empirical Mode Decomposition is proposed, which reveals the relationship between half-wavelength width and pulse time-frequency information. Secondly, according to the response spectrum of the extracted non-pulse time-history, a triangular series is used to generate a stationary time-history, and then the extracted pulse component is added to the time-history, and the intensity envelope is adjusted to obtain the simulated pulse-like ground motion. Finally, the seismic response results of the Bouc-Wen-Baber-Noori model and the three-dimensional finite element model of the high-rise building are validated. It shows that the nonlinear effect of the simulated pulse-like ground motion by this method is close to that of the original natural pulse-like ground motion. The simulated pulse-like ground motion by this method can be used to analyze the inelastic response of various structures.

Seismic performance assessment of high arch dams considering the pulse-like and directionality effects of near-fault ground motions

This paper investigates the pulse-like and directionality effects of near-fault horizontal ground-motion records on the seismic performance of high arch dams. A 3-dimensional arch dam-reservoir-foundation finite-element model is built. Two near-fault bidirectional ground-motion suites (i.e. ordinary and pulse-like suite) are collected. The fault-normal and fault-parallel orientations of the horizontal ground-motion records are rotated to reflect the directionality effect. Nonlinear dynamic analyses are further implemented for the high arch dam excited by both near-fault ground motions with different incidence angles. The results show that the pulse-containing ground-motion records can yield more notable dynamic response and damage for high arch dams as compared to the ordinary records. Moreover, with changing the incidence angles, both the dam dynamic response and damage metrics exhibit periodic variation and constant trends for the pulse-containing and ordinary ground-motion cases, respectively. Therefore, the directionality effect has a significant influence on the seismic performance of high arch dams excited by pulse-containing ground-motion records. Compared with the near-fault ordinary ground motions, the pulse-like ground motions will induce a 40 %-increase in the concrete damage volume of high arch dams. In addition, peak ground velocity could be regarded as a preferable intensity measure for assessing the seismic damage of high arch dams.

Structural state nonlinearity-based design and modification formulae of inerter-based systems

As structural safety emerges as a paramount concern and with the advancement in vibration control technology, a notable gap persists in accurately simulating structural state nonlinearity, especially within the field of inerter-based seismic control technology. Dealing with the need to upgrade the seismic performance of practical nonlinear structures, this study proposes a structural state nonlinearity-based design method for inerter-incorporated civil structures by incorporating the target seismic performance, structural nonlinearity level, and ground motion effects. By establishing mechanical models of inerter-based systems with straightforward parameters and a prototypical bilinear model for the primary structure, governing equations for inerter-incorporated structures were derived. Later, structural state nonlinearity-based design method for inerter-based systems, including optimization criteria and parameter distribution pattern, is elaborated. Simultaneously, this study also provides structural state nonlinearity-based design curves and modification formulae related to structural state nonlinearity and peak ground acceleration of earthquake. Validated using a 10-story multiple-degree-of-freedom (MDOF) structure subjected to earthquakes, the results highlight the effectiveness of the method, emphasizing its potential in controlling seismic responses of structures within the predetermined performance target. In addition, the absolute acceleration mitigation effect of inerter-based systems is investigated. The efficiency and robustness of the proposed method are also verified under near-fault and far-fault earthquakes. In essence, this research pioneers an approach in inerter-based design, bridging structural state nonlinearity, and potentially reshaping seismic control strategies to align with diverse structural states.

The analysis of Yunnan Dayao basin effect based on microtremor test and numerical simulation

AbstractMicrotremor tests and finite element numerical simulations were used to analyze the seismic ground motion effects of the Yunnan Dayao sedimentary basin. The results of the microtremor relative to the reference point spectral ratio (HS/HR) method showed that the spectral ratio curves of each observation point in Dayao basin show multipeak characteristics, indicating that the site consists of different soil layers; the predominant frequencies of each observation point mainly are 6~9 Hz in the basin and there are lots of differences in the predominant frequencies of different observation points, which indicate that the site stiffness of each observation point is different; the differences of spectral ratios between the east–west directions (EW) and the north–south directions (NS) reveal the site's anisotropy. The amplification coefficient characteristics of each observation point in the basin obtained by numerical simulation show that the predominant frequency is 6 ~ 9 Hz; the amplification coefficients of each observation point are different; the edge effect and the focusing effect amplify the seismic ground motion in the basin; the different amplification coefficients of the two sub‐basins reflect the significant effect of the basin soil layers' differences on the seismic ground motion, the site is softer and amplification coefficients are larger; the slope degree of basin edges significantly affects the seismic ground motion near the basins edge, the amplification coefficients of the slope steeper and amplification coefficients larger. This study demonstrates that the microtremor test spectral ratio (HS/HR) method has good reliability applied to the analysis of basin effect and combining the finite element numerical simulation method is more effective in revealing the basin effect mechanism.

Generation of synthetic spectrum-compatible bi-directional ground motions with specific directionality

Ground motions compatible with the maximum-direction response spectrum (RotD100) condition are emphasized in performance-based design and seismic risk assessment of civil structures in different regions. Due to the complex nature and uncertainty of earthquakes, the comprehensive inclusion of essential characteristics of ground motions is crucial. Recently, the directionality effect of horizontal bi-directional ground motions, representing the variation of the response spectral ordinate amplitude along various directions, on the seismic performance assessment of certain structures or key structural elements has received increasing attention in seismic analysis. However, from the seismic design perspective, there is still a lack of a method that can generate bi-directional ground motions comprehensively reflecting the directionality effect. This study focuses on the correction of ground motion directionality when generating synthetic bi-directional ground motions for a given target response spectrum. An efficient and integrated algorithm is proposed. To demonstrate the applicability of the proposed algorithm, three different target RotD100 response spectra are determined according to modern seismic design codes, and 20 pairs of bi-directional ground motions are generated using the proposed algorithm for each target spectrum. It is shown that with the proposed algorithm, the generated motions present a close match to the target RotD100 response spectrum and meet the specific directionality requirement. In addition, due to the iterative modification of the envelope function, the energy of the generated ground motion is also consistent with the scaled natural records.

Effect of Ground Motion on Fragility and Vulnerability of Reinforced Concrete Bridge in Different Soil Conditions

Bridges are essential components of transportation networks, serving as lifelines for the movement of people and goods. The bridges' resilience to natural disasters, particularly earthquakes, is an issue of paramount significance. Yet, a critical knowledge gap exists when it comes to understanding how bridges perform in the challenging terrain of medium-density sandy and clay soils during seismic events. This study seeks to bridge that gap by developing fragility curves that quantitatively evaluate the likelihood of bridge damage or failure across varying levels of earthquake magnitudes. The CSI Bridge v25.0.0 was used to simulate earthquake ground motions specifically within medium-density sandy and stiff clayey soils. Nonlinear time history analyses of the bridge were performed by using 5 different earthquake events with PGA ranging from 0.25 – 1.5g. Fragility analysis is performed to develop seismic fragility curves for the critical part of the bridge for various peak ground acceleration (PGA) in two types of soil conditions. The findings revealed that the deck component is more susceptible to damage than the pier. The impact of seismic activity on medium-dense soil is more significant than on stiff clayey soils in relation to the critical components of the bridge. This result enhances the ability to design bridges that can withstand and recover from seismic events more effectively.

The probabilistic performance-based seismic assessment of concrete bridge piers with SMASC reinforcing bars: Effect of pulse-like ground motion and vertical load-to-capacity ratio

Concrete bridge piers are critical components of bridge structures and their performance under seismic loading is of utmost importance. Traditional reinforced concrete bridge piers have shown limitations in terms of residual deformations and seismic resilience. This has led researchers to explore alternative reinforcement materials, such as Shape Memory Alloy (SMA) coupled with steel reinforcing bars, which have demonstrated promising attributes like energy dissipation as well as self-centering capacity. This study aims to fill this gap by evaluating the performance of concrete bridge piers with SMA-Steel coupled (SMASC) reinforcing bars under various intensities of vertical gravity loads and the action of pulse-like ground motion components, throughout a probabilistic framework. To this end, a group of bridge piers with different reinforcement types, including pure steel and SMASC are considered. These piers are subjected to 55 near-fault (NF) pulse-like records as well as 32 far-fault (FF) ground motions, throughout the Incremental Dynamic Analysis (IDA). The influence of distinct frequency components is analyzed by decomposing NF records into low-frequency pulses and high-frequency residual components. Also, the role of pulse to the 1st modal period of the piers (Tp/T1) is investigated by evaluating the piers’ response under the action of NF records, which were clustered into four groups. Results were assessed by evaluating the intensity measure and capacity of the studied piers at the desired performance objectives according to the FHWA manual. Moreover, the mean annual frequencies of exceeding performance limit states and the confidence levels of meeting performance objectives are studied. The results of the study indicate that the dominance of the component of NF ground motions depends on factors such as the intensity of gravity loads, ground motion characteristics, and the Tp/T1 ratio. The components of NF records within certain clusters of the Tp/T1 ratio are necessary for accurate response assessment, while FF records can be used for conservative design purposes, depending on the level of ground motion intensity and the intensity of applied gravity load. The SMASC-reinforced piers with specific λ factors (i.e. λ = 0.5 or λ = 1.0) and low intensity of gravity loads lead to a higher (1.6 times higher) mean annual frequency of exceeding a limit state, compared to pure steel rebars. Also, the confidence levels for meeting performance objectives vary depending on the ground motions, but, as gravity load intensity increases, confidence levels decrease, particularly for piers with a λ factor of 0.5.

Assessment of the seismic failure of reinforced concrete structures considering the directional effects of ground motions

Seismic intensity measures at different levels significantly impact the seismic damage of building clusters. Reinforced concrete (RC) structures are a type of building widely used in different regions worldwide. A large amount of field seismic damage observation data indicates that within the same seismic intensity zone, the directional effects of varying ground motions lead to significant differences in damage to RC structures on different floors. However, relatively little research has been conducted on estimating the seismic fragility and vulnerability of RC structures considering the directional effects of seismic action. To further study the directional effect of seismic motion on the damage of different floors, this study conducted dynamic time history and spectral analyses on 1472,379 acceleration records in multiple directions obtained from monitoring at nine actual seismic stations during the 2008 Wenchuan earthquake in China. This paper innovatively reports on the actual damage features of RC structures during the Mw6.2 magnitude Jishishan earthquake in Gansu Province, China, on December 18, 2023 (the most severe destructive earthquake in China in 2023) and analyses the influence of earthquake directionality on the damage to different floors of RC structures. A three-dimensional numerical model of a four-story RC frame structure was established using numerical simulation and the finite element method. Different intensity measures were taken to input seismic excitations of different intensities into the RC structure in the 0°, 30°, 60°, and 90° directions, and damage simulation analysis was conducted. The nonlinear dynamic time history curves of structures under multiple directions of seismic excitation in different intensity zones have been developed. Using the interstory stiffness and interstory displacement angle as engineering demand parameters, damage assessment curves and stress clouds for RC structures with 1–4 floors considering different seismic directional effects were generated. The analysis results and major findings indicate that the seismic sequence in the 0° direction has a relatively heavy impact on the first floor of the RC structure in zone IX, which is consistent with the actual field observation results.

Quantifying the effect of pulse-like ground motions on the seismic design of SMA restrained isolation bridges using probabilistic repair cost method

The shape memory alloy (SMA) restrainer serves as an effective but expensive bridge restraining device. However, the impact of pulse effect on SMA design approach under pulse-like ground motions (PLGM) has not been fully quantified in previous studies, which hinders its application in near-fault regions. Therefore, based on the risk probability assessment method throughout the entire life cycle, by accounting for the comprehensive repair cost of each component damage, this paper introduces a parameter design method for SMA restrainer of near-fault bridges that considers structural parameters, pulse parameters, and economic indicators. Firstly, the repair cost ratio (RCR) of bridge system, which means the expenses for repairs expressed as a proportion of bridge replacement costs, was regarded as the life-time optimization goal and overall performance indicator. Secondly, by accounting for near-fault effects, the relationship between RCR and SMA design parameters was established by convolution algorithm of probabilistic seismic hazard analysis, demand analysis and capacity analysis. A novel probabilistic seismic demand model was utilized to quickly determine the RCR of the bridge system under PLGM. Finally, the influence of pulse period on the rational design parameter of SMA restrainer was comprehensively investigated by RCR-based method. A seismic isolation arch bridge was selected as the illustrated case in this article. The results indicate that the rational design parameters of SMA exhibit a pattern of initially rising, then falling as the pulse period increases, reaching the peak value when the pulse period approaches bridge fundamental period. Moreover, the price parameter of SMA significantly affect the optimal design parameters, and the effective range is also recommended.

Study on dynamic and failure characteristics of sand and anti-floating safety of tunnel structures under long-term vibration loads of the Beijing subway

Most research into sand liquefaction has predominantly focused on the effects of earthquake ground motion, with a limited exploration into the possibility of sand liquefaction induced under long-term train vibration loads. Therefore, in order to explore the possibility of saturated sand liquefaction under long-term vibration loads of the Beijing subway, this article selected Tongzhou sand to conduct dynamic triaxial tests and obtained the dynamic and failure characteristics of saturated sand under different confining pressures and dynamic stresses. The test results showed that the confining pressure has a greater impact on sand liquefaction. When the confining pressure exceeds 100 kPa, the possibility of liquefaction of Tongzhou sand is fairly limited. Furthermore, a numerical model of an operating tunnel under the influence of long-term train vibration loads is established, and the dynamic response characteristics of the saturated sand and tunnel structure are studied. Numerical simulation results show that the local liquefaction of sand caused by train vibration will not cause the tunnel structure to float. Under local liquefaction conditions at the extremely shallow tunnel base, the soil did not completely lose its bearing capacity, and the displacement of the soil and structure was still dominated by settlement. Changes in tunnel burial depth have a greater impact on segment structure than train vibration loads. Tunnels with a more than 10 m burial depth will not liquefy in saturated sand within one year, and the segment structure is safe. The research results can provide a reference for the anti-floating safety of tunnel structures in similar saturated sand strata.

A data-driven approach for structural integrity assessment of prestressed concrete containment vessel considering the effect of vertical ground motions

As a final barrier against the release of radioactive material, the prestressed concrete containment vessel (PCCV) plays an important role in the nuclear power plant (NPP). When subjected to seismic loads, its structural performance requires high structural integrity. During an earthquake, the PCCV experiences ground motions (GMs) consisting of horizontal and vertical components in a global coordinate system, and its structural integrity is probably overestimated if only the horizontal component is considered in numerical analyses. In this study, a novel cumulative damage index is first employed to quantitatively assess the structural integrity of PCCVs. Accordingly, the failure probability of structural integrity of the PCCV is investigated by incremental dynamic analysis (IDA) and further seismic fragility analysis considering the effect of vertical ground motions (VGMs). The results show that the effect of VGMs on structural integrity of PCCVs is gradually non-negligible with the increase of vertical intensity. Moreover, an accurate cumulative damage prediction model for the PCCV is established based on eight mainstream machine learning (ML) algorithms, and the necessity of incorporating vertical intensity measures (IMs) in ML models is investigated. The results show that the ML model considering the vertical IMs is superior in capturing the cumulative damage of the PCCVs. The best estimates are obtained by GB with R2 of 0.912, MAE of 1.301, MSE of 6.186, and RMSE value of 2.487. Finally, the SHapley Additive exPlanation (SHAP) method is adopted for interpreting the prediction results of the optimal ML model to assess the effect of each IM and its interactions on the generalization performance of the model. The proposed ML-based cumulative damage prediction model for PCCVs considering the effect of VGMs enables an accurate quantitative assessment on structural integrity of PCCVs. This provides an important reference for evaluating the potential environmental hazard due to the leaking of radioactive materials.

Amplification effects of ground motion due to the local geology of the building site in the cities of Kyiv, Kryvyi Rih, Odesa

The results of the research presented in the article elucidate the importance of taking into account the amplitude-frequency characteristics of soil stratum models in the context of seismic safety of construction objects on the territory of Ukraine, in different regions. The presented results of the analysis of the calculated amplitude-frequency characteristics of models of soil environments for different regions of Ukraine reveal that the amplification of vibrations by soils has a complex nature that depends on many factors and can differ significantly for different construction sites. We have shown that during the earthquake-resistant design of buildings and structures, it is necessary to properly take into account the properties of soil complexes under the research site, which can significantly increase oscillations at “resonant” frequencies. The article examines in detail the features of amplitude-frequency characteristic models of soil strata for different geological conditions in Kyiv, Kryvyi Rih and Odesa. The purpose of this study is to compare these characteristics and develop recommendations for reducing risks associated with seismic hazards.

Seismic Response of Utility Tunnel in Trapezoidal Backfilled Soil Under P Wave and Amplification Effect of Ground Motion

ABSTRACT For the seismic risk of utility tunnel in trapezoidal backfilled soil and its possible amplification effect of ground motion, the seismic response of utility tunnel in trapezoidal backfilled soil under P wave is studied by a high-precision indirect boundary element method (IBEM) with the idea of “partition fit.” The results show that the peak surface displacement appears on the backfill surface, and the softer the backfilled soil, the greater the peak surface displacement; the peak vertical displacement at oblique incidence is generally smaller than that at vertical incidence; the existence of utility tunnel can restrain the incidence wave to a certain extent, especially for the low-frequency wave; the peak displacement and stress of utility tunnel in the soft backfilled soil are all greater than that in stiff backfilled soil; the peak stress of utility tunnel at oblique incidence is greater than that at vertical incidence; the stress concentration occurs at the axillary corner; and the stress in the inner wall of utility tunnel is greater than that in the outer wall. The similar conclusions could be further confirmed from the time history analysis. The research results can provide some reference for the seismic design of utility tunnel in the backfill site and the evaluation of seismic performance of near surface pipeline, etc.

Earthquake scenario-specific framework for spatial accessibility analysis (SAA) of emergency shelters: a case study in Xichang City, Sichuan Province, China

The spatial accessibility of emergency shelters, indicating the difficulty of evacuation and rescue, is crucial for disaster mitigation and emergency management. To analyze accessibility, an effective approach is to evaluate the service capacity of emergency shelters. Multifaceted factors were employed to enhance the quantitative accuracy of accessibility indicators. However, scenario-specific analysis has not been emphasized. Considering the devastating potential of great earthquake disasters, we cannot ignore the impact of these scenarios on emergency shelter accessibility, especially in areas with high seismic risk. In this study, we developed an earthquake scenario-specific framework for spatial accessibility analysis (SAA), which integrates the service capacity of emergency shelters and the impact of strong ground motion and fault rupturing. We applied this framework to the urban area of Xichang City in Sichuan Province, western China. Xichang City, located in the linked area of the Anninghe fault and Zemuhe fault with many extreme historical earthquake disaster records, is prone to high seismic risk. We firstly collected emergency shelter and road network data in Xichang City. We then applied SAA based on the road network, using the network analysis method. After that, we analyzed the impact of strong ground motion on accessibility and generated the setback zone of fault rupturing. We integrated the effect of strong ground motion on accessibility within the setback zone of active faults. Finally, we generated a comprehensive accessibility map, considering both the predicted strong ground motion and potential fault rupturing. Our results show that the accessibility level changed in several towns of urban Xichang City due to strong ground motion and fault rupturing. The accessibility level decreased in Lizhou, Xingsheng, and Anning Towns. For areas with mapped fault lines, the accessibility level is Very-Low. Our results demonstrate the impact of earthquake damage on the accessibility of emergency shelters and the complexity of evacuation in earthquake scenarios. In general, we added earthquake rupturing and ground motion characteristics into the SAA framework. This framework will help us enhance the reliability of SAA and the feasibility of seismic vulnerability evaluation.

Seismic response of a ground-bridge structure system in horizontal and inclined liquefiable site to near-fault pulse-like ground motions

Previous earthquake events have indicated that bridge structures are more vulnerable to severe damage when subjected to near-fault pulse-like (NF-P) ground motions. Structural seismic damage will be exacerbated when bridges are located in liquefiable site. Meanwhile, the seismic response of bridges located in inclined liquefiable site is different from that of bridges in horizontal liquefiable site. This study focuses on exploring the seismic response of a ground-bridge structure system located in horizontal and inclined liquefiable site to the NF-P ground motions. The seismic response of the whole system to the near-fault non-pulse-like (NF-NP) and far-field (FF) ground motions is studied for comparison. Two three-dimensional (3D) finite element (FE) models of the ground-structure system considering soil-pile interaction are developed. They are associated with the horizontal and inclined liquefiable site, respectively. The seismic responses of the ground-bridge structure system to the three different types of ground motions (i.e., NF-P, NF-NP and FF) are comprehensively evaluated from two perspectives. On the one hand, the seismic time history responses of the ground-bridge structure system under single representative ground motion are comprehensively assessed. On the other hand, the average responses of the ground-bridge structure system under multiple types of ground motions are explored. The results reveal that in contrast to the NF-NP and FF ground motions, the NF-P ground motions have more significant effect on various responses of the ground-bridge structure system. In addition, compared to the bridge in horizontal liquefiable site, the bridge in inclined liquefiable site exhibits larger seismic responses. Therefore, the velocity pulse effect of the NF-P ground motions and the liquefaction effect of the inclined site need to be emphasized in structural seismic design.

Running Safety Assessment of a High-Speed Train on Bridges During Braking Under Near-Fault Ground Motions

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 0.2[Formula: see text]g, 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 0[Formula: see text]g and 0.1[Formula: see text]g. 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 250[Formula: see text]km/h, which is more favorable to the smooth deceleration of the train. When the train speed is 400[Formula: see text]km/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.

Seismic fragility of vertically irregular gravity column-core tube structure subjected to pulse-like ground motions

The effects of the pulse-like ground motion and structurally vertical irregularity on the seismic fragility of the new gravity column-core tube structural system are investigated. Based on the shaking table test, the finite element parameters are verified. By changing the stiffness ratio of the first story to the second story, the typical vertically irregular gravity column-core tube structure models of 20-, 30- and 40-stories are established. Selecting 10 pulse-like and 10 corresponding non-pulse-like ground motion records, the incremental dynamic analysis and seismic fragility analysis are performed to these structures employing CANNY program. The results show that the maximum inter-story drift ratio (θmax) and the probability of exceeding the limit state (Pf) of each structure under pulse-like cases are significantly greater than those under non-pulse-like cases. From slight damage to approaching collapse state, the difference in seismic fragility curves between pulse-like cases and non-pulse-like cases is gradually amplified. It is suggested that the seismic strength reduction factor of these new type of structures be reduced properly to consider the pulse-like ground motion effect. With the stiffness ratio decreases, θmax and Pf have an increasing trend. However, the increasing quantity is small, which may be due to the effect similar to the isolation in the first story. As a limit value of vertical irregularity in the first story, the stiffness ratio of 1.5 provisioned in the code is conservative. To give consideration to both the safety and the economy, it is recommended to lower the limit value to about 1.2 for the gravity column-core wall structures with stiffness irregularity at the first story.