Effects Of Ground Motions Research Articles

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.

Life-cycle seismic performance of Q690 steel columns with H-section under various bi-directional cyclic loading paths

The ageing effect in the life-cycle assessment should be considered for the high-strength steel structures constructed in corrosive environments and high-seismicity zones. Additionally, the structures can suffer multi-dimensional seismic excitations because of the spatial effect of ground motions. Therefore, this study aims to investigate the impact of different loading protocols on the mechanical properties of Q690 steel columns with H-section during the whole life-cycle. Firstly, numerical methods considering time-varying corrosion process are used to simulate the ageing steel columns. After that, the nonlinear hysteretic behaviors of the ageing steel columns under different loading protocols are investigated. The factor of resistance degradation (the degree of degradation of ultimate resistance) is employed to quantify the effect of loading protocols on ageing steel columns. Finally, the biaxial ultimate interaction curve considering the ageing effect and a practical design process are proposed. The findings demonstrate that the steel columns exhibit different mechanical properties under various loading protocols, and the coupling direction of bi-directional displacement loads influences the degree of degradation of ultimate resistance. As service time increases, the factor of resistance degradation of steel columns gradually reduces by up to 40%. The proposed biaxial ultimate interaction curve has acceptable accuracy. These findings emphasize the importance of employing the unfavorable loading protocols in conducting the seismic design of the steel columns in different life-cycle stages.

Seismic safety assessment of dam slopes considering rockfill softening characteristics, shear strength uncertainties, and stochastic ground motion

The stability of the dam slope is one of the crucial indicators for maintaining the overall stability and reliability of the dam. The seismic stability response analysis of the dam slope involves a significant number of factors that introduce uncertainty, primarily including the stochastic ground motion and the uncertainty of the shear strength parameters of rockfill. Furthermore, the rockfill material is susceptible to strain-softening behavior at low confining pressures when subjected to ground motion, which exacerbates its progressive failure. Therefore, the assessment of seismic safety for dam slopes should give due consideration to this characteristic of rockfill material. This study extensively explores the influence of rockfill softening, stochastic ground motion, and the variability of rockfill shear strength parameters on the stability of the dam slope. Conducting probabilistic analysis in conjunction with the generalized probability density evolution method (GPDEM), the findings suggest that it is imperative to evaluate the safety characteristics of the dam slope by considering the coupled effects of stochastic ground motion, the variability of shear strength parameters, and the effect of rockfill material softening. Based on this, a preliminary dam slope failure classification was proposed, and a framework for dam slope seismic safety assessment was established.

Interaction-performance-driven design of negative-stiffness friction pendulum systems for aboveground structure–connected underground structure–soil system with ground motion effects

Within the transit-oriented development framework, aboveground structure–connected underground structures (ASUS) have been widely constructed in urban areas; however, abrupt stiffness changes and complex soil–structure interactions could cause structural damage or business disruption after earthquakes. In this study, to address these challenges, a novel approach is proposed that employs negative stiffness, damping elements, and friction pendulum bearings to enhance the overall performance of ASUS. An interaction-performance-driven design procedure and parameter selection methodology are developed to simultaneously upgrade multiple performance aspects of ASUS. A mechanical model of the negative stiffness amplification system-enabled friction pendulum system (NSAS-FPS) is constructed. The theoretical basis of the equivalent negative stiffness and enhanced energy dissipation effects is elucidated, and a finite element model of the NSAS-FPS-incorporated soil–ASUS interaction system is established. Extensive parametric, robustness, and correlation analyses against short/long-period ground motions are conducted to provide a comprehensive performance assessment framework. Then, an interaction-performance-driven design principle aimed at multiperformance upgrading of aboveground and underground structures is developed with proposed parameter selections and applied in a case study. These results indicate a significant improvement in vibration control for both aboveground and underground structures when utilizing NSAS-FPS compared to utilizing conventional FPSs with the same design. By following the proposed design procedure and parameters, the NSAS-FPS demonstrates enhanced efficiency in isolating energy dissipation and robustness in seismic isolation, as well as resistance against overturning, irrespective of variations in structural masses and functionalities. While the advantages of the NSAS-FPS include its ability to mitigate the effects of stochastic earthquakes, the extent of the performance improvement may decrease during long-period earthquakes. Therefore, the velocity characteristics of seismic excitations need to be carefully incorporated into the NSAS-FPS design, particularly when targeting specific demands for the isolation-layer performance within ASUS.

Characteristics of torsional ground motions obtained for Turkey and their appraisal against Eurocode 8

In current engineering practice, the torsional effects of ground motions are only considered implicitly through “accidental eccentricity coefficients". In seismic design codes, these coefficients account for not only the unintended (or uncertain) asymmetric distributions of structural mass and stiffness in the plan but also the torsional components of ground motions. The torsional effects may develop due to wave passage effects or the incoherency of translational ground motions along the foundation systems. While it is possible to obtain torsional components of ground motions directly from seismic records with modern instruments, such sensors are uncommon. Therefore, several numerical procedures have been proposed in the literature for estimating torsional components of ground motions from translational measurements. In this study, the Single Station Procedure (SSP)—based on the deconstruction of translational ground motions into body waves and the subsequent reconstruction of rotational ground motions—is employed to obtain torsional ground motions for seven different seismic events in Turkey. Additionally, the corresponding accidental eccentricity coefficients that can cause the same response modification with torsional ground motions are determined. First, a conventional procedure is utilized to obtain the corresponding accidental eccentricity coefficients. Various drawbacks of the conventional procedure, such as negative eccentricity coefficients, are addressed. Then, a relatively obscure definition of accidental eccentricity is revived to propose a novel procedure for determining accidental eccentricity coefficients. It is observed that the proposed procedure yields higher values for the accidental eccentricity coefficients than the conventional procedure. It also observed that the torsional spectrum provided in Eurocode 8 provisions requires higher eccentricity values than those implied by the recorded ground motions from Turkey.

Seismic response of RC bridges under near-fault ground motions: A parametric investigation

Natural disasters such as earthquakes can potentially harm bridges and incur significant socioeconomic losses. This study examines the effect of near-fault ground motions on reinforced concrete bridges, specifically the variation in the seismic performance with the height, aspect ratio, and longitudinal reinforcement. A suite of 332 near-fault ground motions is used to evaluate the performance of 60 bridge models in OpenSees, and the seismic responses are measured in terms of pier curvature ductility, maximum bearing deformation, and deck displacement. Linear regression analysis is used to generate probabilistic seismic demand models and fragility curves corresponding to different damage states. Expected behaviors are displayed within the models grouped with respect to height classes. Since the column diameters are based on aspect ratios, the effect of taller columns reduces the exceedance probabilities. This brought forward a need to define the damage states for tall columns in a manner different from short or medium columns. Moreover, this study underscores the need to update HAZUS fragility median values for near-field seismic response of RC bridges.

Exploring the Effect of Near-Field Ground Motions on the Fragility Curves of Multi-Span Simply Supported Concrete Girder Bridges

Investigating the impact of near-field ground motions on the fragility curves of multi-span simply supported concrete girder bridges is the main goal of this paper. Fragility curves are valuable tools for evaluating seismic risks and vulnerabilities of bridges. Numerous studies have investigated the impact of ground motions on the fragility curves of bridges. Ground motions are commonly categorized into two sets, based on the distance of the recorded station from the seismic source: far-field and near-field. Studies examining the influence of near-field records on bridge fragility curves vary depending on the specific bridge type and type of fragility curve being analyzed. Due to the widespread use of multi-span simply supported concrete girder bridges in the Central and Southeastern United States, this study makes use of this bridge type. This research investigates the component fragility curves for column curvatures, bearing deformations, and abutment displacements by employing 3-D analytical models and conducting nonlinear time history analysis. These curves illustrate the impact of near-field ground motions on different components. The component fragility curves for two sets of records, 91 near-field ground motions and 78 far-field ground motions, were obtained and compared. These findings demonstrate that near-field ground motions have a greater damaging effect on columns and abutments than far-field earthquakes. When it comes to bearing deformations, the far-field earthquake impact is more severe at lower intensities, whereas the impact of the near-field ground motion is stronger at higher intensities.

Study on the seismic characteristics of piers considering site conditions and hydrodynamic effect

Sea-crossing bridges face complex site environments compared to onshore bridges, with the marine environment significantly influencing seismic responses. Despite this, current seismic design for these bridges relies on onshore earthquake records. Therefore, investigating the impact of seawater layers and site conditions on sea-crossing bridge seismic performance is crucial. This paper investigates the influence of characteristics of offshore ground motion, site conditions, and hydrodynamic effect on the seismic performance of piers. Initially, based on the validated finite element model, 5 offshore and onshore strong ground motion records from K-NET were selected for assessing the seismic performance of piers. Subsequently, the effects of the water depth and site conditions on the seismic responses of piers were investigated. Finally, the effects of the section size, section shape, and boundary conditions on the piers were investigated. The result shows that the seismic response of piers under offshore ground motion exceeds that under onshore ground motion. In addition, the seismic response of the pier increases with greater water depth, while they exhibit a slight decrease with increasing soil depth. Notably, the larger the section size, result in higher the hydrodynamic pressure, and square piers experience greater hydrodynamic pressure compared to circular piers.

Near-fault ground motion effect on self-centering modular bracing panels considering soil-structure interaction

This study investigates the nonlinear seismic response behavior of self-centering modular steel bracing panel (SCMBP) systems subjected to near-fault ground motion records, considering the soil-structure interaction (SSI) effect. Analytical formulas for the load-displacement relationship of an SCMBP were validated through nonlinear 3D continuum finite element analysis while a simplified 2D wireframe model utilizing a constitutive spring model was verified by the 2D refined finite element model and subsequently adopted for time history analysis of the SCMBP structures with SSI effect. Based on the nonlinear time history analysis of a 6-story prototype building subjected to a suite of near-fault ground motions, the prototype structure is found to be able to re-center itself even under near-fault ground motion scaled to the design basis earthquake (DBE) level while frame members remain undamaged, except for fuse devices. Additionally, SSI reduces inter-story drift ratios under both far-field and near-fault ground motions. The findings provide insights into the promising performance of using SCMBP systems as a seismic strengthening system for sites with potential SSI effects and near-fault earthquake impact. The findings of this study can be insightful to other self-centering systems with flag-shaped story shear hysteresis.

Ground-motion effects on liquefaction response

This article evaluates the influence of ground-motion characteristics on the liquefaction response of free-field level-ground deposits. Ground motions imposed on liquefiable soils have historically been characterized by the peak ground acceleration (PGA). In simplified procedures for liquefaction evaluation, the use of the ground surface PGA can be justified by the fact that it is closely related to the peak shear stresses developing in the critical zone for liquefaction manifestation, at shallow depths. In nonlinear dynamic analysis (NDA), however, such simplified characterization of the input motion using the bedrock-level PGA can result in large record-to-record variability in the computed response. Record-to-record variability can be substantially reduced by employing more appropriate ground-motion intensity measures (IMs) for specific aspects of the liquefaction response observed in NDA. Among 25 IMs examined in this study, the Modified Acceleration Spectrum Intensity (MASI), defined as the integral of the acceleration spectrum over periods 0.1–1.5 s, is found to be the most efficient IM for the prediction of the pore-pressure response of liquefiable deposits, whereas Velocity Spectrum Intensity (VSI) ranks among the best-performing IMs for response parameters related to ground deformations. Importantly, such “multiple-period spectrum IMs” are shown to perform consistently better than several highly-regarded time-integrated IMs (e.g. Arias intensity, CAV). Conclusions and recommendations are drawn on the basis of a comprehensive series of NDAs involving 180 input motions and 13 deposit models based on characteristic soil profiles from Christchurch.

Effects of near-fault and far-fault ground motions on nonlinear dynamic response and seismic damage of masonry structures

This study explores the seismic behavior of masonry buildings in close proximity to a fault rupture as compared to those located farther away. It takes into account the distinctive features of near-fault ground motions, such as forward directivity and the fling effect, which have the potential to cause significant earthquake-related damage. The study employs a dataset comprising 100 earthquake records, which represent both near-fault and far-fault ground motions and conducts an analysis of nineteen masonry buildings with varying typologies. Analytical models for each of these buildings are constructed using experimental data concerning the quality of masonry materials. Nonlinear static and dynamic analyses are carried out to evaluate the buildings' capacity to withstand seismic deformations and the extent of damage incurred. The findings indicate that near-fault ground motions exert a more significant influence on the dynamic response and result in greater damage to masonry structures when compared to far-fault ground motions.

Shaking table test of prestressed high-strength concrete pipe piles reinforced with non-prestressed steel reinforcement

Prestressed high-strength concrete piles reinforced with non-prestressed steel reinforcement (PRHC piles) have been developed to improve their seismic performance. In this study, the seismic response and failure mechanism of PRHC piles was investigated using a shaking table test. The dynamic characteristics, dynamic soil pressure, superstructure response, acceleration magnification factors, maximum curvature ductility demand, bending moment response, and failure mode identification of the PRHC piles were determined. The performance of PRHC piles was compared with that of prestressed high-strength concrete pipe (PHC) piles, which showed that the PRHC piles experienced higher energy dissipation and lower maximum curvature ductility demands than PHC piles. In addition, the PRHC piles suffered bending failure at the upper-middle positions, and the plastic zones were higher than those of the PHC piles. The adverse effects of long-period and pulse-type ground motions on pipe piles should be considered in designing for strong seismic events. The addition of non-prestressed reinforcement to a pipe pile allows longer segments of the pipe pile to be involved in providing resistance.

Track-bridge deformation relation and interaction of long-span railway suspension bridges subject to strike-slip faulting

During earthquakes, the long-span railway bridges crossing active faults are more vulnerable because of the combined effects of pulsed ground motions and surface dislocations. To study the track-bridge deformation and interaction of long-span railway suspension bridges crossing the strike-slip faults, the refined finite element model of a ballasted track-bridge-pile-soil coupled system was established using the nonlinear finite element software ANSYS/LS-DYNA. A detailed and systematic numerical simulation was conducted from the soil cracking and compression during the ground surface rupture, pile–soil interaction, and three-dimensional track constraints to track-bridge deformation relationships and interactions. One-dimensional wave propagation theory was employed to derive the ground motions on the bedrock according to ground surface-measured seismic records. The influences of the fault-crossing angle (FCA) and permanent ground rupture displacement (PGRD) on the seismic responses and track-bridge interaction were analysed by considering the pile–soil interaction and site response effect. A method for calculating the track curvature radius based on track deformation is presented to evaluate the running traffic conditions of the trains. Additionally, the stability of the ballast bed was estimated using the track-bridge relative displacement. The conclusions drawn can be applied in practical seismic design and train running safety assessment of long-span railway suspension bridges crossing the strike-slip faults.

Effect of site specific soil characteristics on the nonlinear ground response analysis and comparison of the results with equivalent linear analysis

Damages occurring during earthquakes may vary depending on the ground conditions in which the earthquake waves pass, the magnitude of the earthquake, the focal depth of the shaking and as well as the structural characteristics. Regional seismicity, ground movement and behavior of local soil conditions are important in earthquake-resistant building designs. Local site conditions consist of the layering, bedrock depth, and dynamic and topographic characteristics of soil that alter the bedrock waves through the soil profile during an earthquake. The change occurs in terms of amplitude, frequency and the time when the peak happens during the wave propagation. This initiates a big difference between the surface and bedrock motion. The behavior of the soil under cyclic loads resulting from seismic action is non-linear. This study aims to demonstrate the effects of strong ground motion by taking into account the nonlinear behavior of the soil layers. In addition, the results obtained from the equivalent linear and non-linear methods were compared. The results of the study showed that the characteristics of soil layers and strong ground motion (frequency content and duration) significantly affect the field response analysis and generally larger spectral parameters (about %20) have been obtained with the equivalent linear method compared to the nonlinear behavior. Finally, empirical models to estimate the soil amplification reflect different compared to the site specific analysis.

Experimental study on seismic responses of a curved bridge considering the effect of pulse and pulse duration

To investigate the effects of pulse-like ground motions on curved bridges, this study conducted a shake table test on a 1/10 scaled curved bridge model while considering the effect of pulse and pulse duration. The experimental results revealed that the seismic responses of curved bridges under pulse-like ground motions were greater than those under normal ground motions. The amplification effect caused by pulse-like ground motions was more pronounced in better site conditions. The effect of pulse duration on the responses of curved bridges was also significant and varied with the pulse duration. Therefore, seismic design should consider not only the pulse effect but also the difference in pulse duration. Furthermore, when curved bridges are subjected to pulse-like ground motions, bents with smaller stiffness and the outer bearing are more likely to be damaged and should receive more attention in seismic design.

Assessment of Near-Field Strong Ground Motion Effects on Offshore Wind Turbines Resting on Liquefiable Soils Using Fully Coupled Nonlinear Dynamic Analysis

Assessment of Near-Field Strong Ground Motion Effects on Offshore Wind Turbines Resting on Liquefiable Soils Using Fully Coupled Nonlinear Dynamic Analysis

Dynamic Response and Running Safety of High-Speed Railway Train–Track–Bridge System Under Near-Fault Pulse-Type Ground Motion

The pulse effect of near-fault ground motion has asevere threat to high-speed railway train running on bridge. Current research generally relies on numerical simulation and lacks physical test data. In this paper, a scale indoor physical test of high-speed train running on bridge is conducted and dynamic characteristics of high-speed railway train–track–bridge system under near-fault pulse-type ground motion are explored. The bridge of the physical test is excited by shaking table with lateral inputs of near-fault pulse-type ground motion, pulse-free ground motion and far-field ground motion. A corresponding numerical model is established and validated by the test data. Then, the influence regularities of pulse effect on system dynamic response and running safety indexes are explored under different peak ground acceleration (PGA) and train speeds using data of the physical tests and the numerical simulation comprehensively. Results suggest that compared to the near-fault pulse-free ground motion and the far-field ground motion, the near-fault pulse-type ground motion leads to larger lateral beam displacement, lateral train acceleration, and running safety indexes in different degrees. And from the data results of this paper, its lateral wheel–rail force and derailment coefficient are the first to break through the limit values. By studying the parameter sensitivity of lateral train acceleration, it was found that under the near-fault pulse-type ground motion, the lateral train acceleration is significantly more sensitive to changes of train speed and PGA. From the perspective of energy, the near-fault pulse-type ground motion results in spectrum intensity (SI) indexes which are larger and improve faster with the increase of PGA than other ground motions. This indicates that it inputs significantly more energy into the high-speed railway train–track–bridge system, although it may not excite larger lateral beam acceleration.

The Effect of Vertical Ground Motion in Dynamic Analysis for Near Fault Area in Yogyakarta

Indonesia is surrounded by three major tectonic plates which are Indian-Australian, Eurasian and Pacific tectonic plates. Consequently, Indonesia is prone to seismic hazard. Horizontal ground motion has taken a major role in conducting nonlinear time histories analysis or in assessing liquefaction potential. However, for site near fault area, vertical ground motion can be quite significant and cannot be neglected. This paper aims to evaluate the effect of vertical ground motion in the near fault area by conducting dynamic analysis using MIDAS GTS NX. UBC Sand model is employed to model liquifiable material. Standard penetration test, laboratory test and downhole seismic tests are conducted at the site in order to characterize the shear wave velocities and properties of the soil at the area and to determine the thickness of the liquifiable layer. For this paper, two dynamic analyses will be conducted. For first analysis, only horizontal ground motion is applied to the model while in the second analysis, both horizontal and vertical ground motion will be applied. Based on dynamic analysis result, the horizontal surface motion and horizontal surface response spectrum that is propagated using bi-directional time histories will have bigger acceleration if being compared by only using horizontal time histories.

Effect of Traveling Waves on Seismic Behavior of Fault-Crossing Transmission Tower-Line Systems

Ultra high voltage (UHV) transmission tower-lines systems (TTLSs) are responsible for the crucial function of transmitting and distributing electrical power over long distances, which inevitably traverse active tectonic faults when passing through seismic areas. This paper investigates the seismic behaviors of the fault-crossing UHV TTLSs, taking into account the traveling wave effects of fault-crossing ground motions. Furthermore, three scenarios (i.e. the fault located at the midspan, the side span, and the one side) according to the location of the faults relative to the TTLSs, are designated to investigate the effects of fault-crossing locations on the seismic behaviors of the fault-crossing TTLSs. The results indicate that the traveling wave effects may amplify or weaken the seismic responses and collapse of the near-fault and fault-crossing TTLSs, and the effects on the longitudinal displacement responses of the TTLS are significantly greater than those in the transverse direction, but they do not affect the distribution of the collapse weak position of the TTLSs across the fault. Besides, the effect of traveling waves on the seismic behaviors of the transmission tower further away from the fault is greater than that relatively closer to the fault. This study of the impact of the traveling wave effects and fault-crossing locations on the TTLSs serves as a valuable reference for seismic behaviors of the UHV TTLSs crossing faults.