Variability Of Ground Motion Research Articles

How Does Thermal Pressurization of Pore Fluids Affect 3D Strike-Slip Earthquake Dynamics and Ground Motions?

ABSTRACT Frictional heating during earthquake rupture raises the fault-zone fluid pressure, which affects dynamic rupture and seismic radiation. Here, we investigate two key parameters governing thermal pressurization of pore fluids – hydraulic diffusivity and shear-zone half-width – and their effects on earthquake rupture dynamics, kinematic source properties, and ground motions. We conduct 3D strike-slip dynamic rupture simulations assuming a rate-and-state dependent friction law with strong velocity weakening coupled to thermal-pressurization of pore fluids. Dynamic rupture evolution and ground shaking are densely evaluated across the fault and Earth’s surface to analyze the variations of rupture parameters (slip, peak slip rate, rupture speed, and rise time), correlations among rupture parameters, and variability of peak ground velocity. Our simulations reveal how variations in thermal-pressurization affect earthquake rupture properties. We find that the mean slip and rise time decrease with increasing hydraulic diffusivity, whereas mean rupture speed and peak slip-rate remain almost constant. Mean slip, peak slip-rate, and rupture speed decrease with increasing shear-zone half-width, whereas mean rise time increases. Shear-zone half-width distinctly affects the correlation between rupture parameters, especially for parameter pairs (slip, rupture speed), (peak slip-rate, rupture speed), and (rupture speed, rise time). Hydraulic diffusivity has negligible effects on these correlations. Variations in shear-zone half-width primarily impact rupture speed, which then may affect other rupture parameters. We find a negative correlation between slip and peak slip-rate, unlike simpler dynamic rupture models. Mean peak ground velocities decrease faster with increasing shear-zone half-width than with increasing hydraulic diffusivity, whereas ground-motion variability is similarly affected by both the parameters. Our results show that shear-zone half-width affects rupture dynamics, kinematic rupture properties, and ground shaking more strongly than hydraulic diffusivity. We interpret the importance of shear-zone half-width based on the characteristic time of diffusion. Our findings may inform pseudodynamic rupture generators and guide future studies on how to account for thermal-pressurization effects.

Infrastructure seismic risk assessment: an overview and integration to contemporary open tool towards global usage

Infrastructures are critical for the functioning of society. Due to globalization, damages between different components of infrastructure systems can cross international boundaries, resulting in broad economic and social impacts. Hence, it is fundamental to develop powerful tools for the assessment of infrastructure risk, considering a wide spectrum of uncertainties. Past studies covering infrastructure risk assessment are limited to a few countries, partly because for assessing the infrastructure risk, issues due to the complexity of the systems, like paucity and heterogeneity of the data and methods, the consideration of dependencies between components and systems, modeling of ground shaking in terms of scenario and probabilistic approach, taking into account site effects, spatial variability and cross correlation of ground motion at the urban scale, as well as consideration of risk metrics tailored to infrastructure, still remain partially or not properly answered. Moreover, the presently available infrastructure risk assessment tools are not sufficiently illustrative, user-friendly, and comprehensive to meet actual needs. To this end, the paper making an overview of these issues proposes a comprehensive approach that leverages the main strength of existing infrastructure risk methodologies, integrating them into a powerful open-source tool and providing common platform from hazard to risk analysis that will serve for global and easy usage. The methodology and its implementation are illustrated through a test-bed study of the water supply network of the city of Thessaloniki in Greece, considering an Mw 6.5 scenario of the 1978 Thessaloniki earthquake and an event based probabilistic approach and, simultaneously evaluating the sensitivity of cross spatial correlation.

Simulation of spatially varying ground motion of urban buildings based on wavelet packet neural network

AbstractSite‐structure cluster interaction (SSCI) has a significant effect on the seismic response of densely distributed buildings, and rationally and effectively quantifying its effect when modelling the urban seismic damage can provide more optimal decisions to mitigate earthquake disasters. This paper focuses on the input motion of the structures, by extracting the main influential parameters of SSCI and adopting the loosely typed wavelet packet neural network to rapidly simulate the spatially varying ground motion in the urban environment. In the proposed framework, the wavelet packet energy ratio is presented to describe the variation of ground motion characteristics and used as the sole output to carry out the multi‐resolution spectral modulation, and the training samples were accumulated by a validated finite element simulation method. The developed surrogate model considers the effects of a series of factors, including the earthquake intensity, site condition, configuration of structure cluster, structural dynamic characteristics and spacing, and is superior to the one using conventional artificial neural network. It is verified by a virtual test that the waveshape and spectral features of the predicted ground motion agree well with the target result with an error of peak acceleration being only 1.23%. The suggested approach has the advantages of better modulation precision and lower sample size requirement. Moreover, it is almost zero cost to use the developed surrogate model to correct the ground motion of urban buildings and to consider the influence of SSCI, and the structural seismic response can be more factually displayed in the time and space domains. These specialties make it a promising technique in the rapid assessment of urban seismic damage.

Optimal design of cable-stayed bridge and its approach spans under spatially varying ground motions

The out-of-phase vibration between neighboring structures owing to their different vibration characteristics and spatially varying seismic excitations may result in strong impact between the adjacent structural components, which might result in detrimental damage to the structures. To preclude such damage, the gap size of the expansion joint and the vibration period ratio between the adjacent structures should be carefully selected. Herein, the framework of performance-based seismic design (PBSD) is extended to optimize the gap size and period ratio between the cable-stayed bridge and its approach spans under the spatially varying ground motions. Considering the computational burden, an equivalent cable-stayed bridge model is proposed and verified, and then adopted in the optimization process. Based on the multi-stripe analysis (MSA) method, the component fragility curves (pylons, bearings, and local damage) for the typical cable-stayed bridge are derived, and then the corresponding structural fragility functions, namely, repair cost ratios (RCRs) are derived. The optimal gap size and period ratio between main bridge and approach spans could be identified by the proposed optimization framework under both uniform and spatially varying excitations. The analytical results demonstrated that the optimal gap size and period ratio depend on the earthquake characteristics and the excitation methods. The optimized RCR values of the bridge subjected to the spatial varying ground motions are much larger than those of bridge under the uniform excitation.

Improvement of tailings impoundment seismic and post-seismic stability using densification and waste rock inclusions

Tailings impoundments are often prone to failure due to various causes related to complex loading conditions. For instance, tailings impoundments can fail during or after a seismic event, mainly because of the liquefaction of loose, cohesionless tailings. To improve the seismic stability of impoundments, the density of the tailings can be increased or waste rock inclusions (WRI) can be added in the impoundment. This paper presents the results of numerical analyses of the impoundments loaded with a variety of ground motions with different frequencies, scaled at two different levels of intensity representative of two mining regions of Eastern Canada. The results show that the conventional impoundments are subjected to medium to high displacements at the end of shaking; these show a high probability of rupture during the earthquake or in the post-seismic phase. Tailings densification can decrease the volume of liquefied tailings and displacements during the seismic phase but does not significantly reduce the probability of post-seismic failure. WRI can slightly reduce the volume of liquefied tailings, depending on the intensity of the motions, but the reinforcement reduces significantly the lateral displacements; impoundments with WRI show even better performances during the post-seismic phase. The use of WRI is deemed a good approach to ensure the seismic stability of tailings impoundments and reduce the risk of seismically induced failure.

A new framework for ground motion selection for structural seismic assessment

Performance-based structural seismic assessment generally requires the selection of ground motions wherein the target acceleration response spectrum (Sa) should be matched in a desired period range. The pros and cons of the commonly used uniform hazard spectrum (UHS), conditional mean spectrum (CMS) and conditional spectrum (CS) are thoroughly examined. Aiming at combining the merits and overcoming the challenges of these methods, a new framework is proposed to construct a series of conditional target spectra for selecting ground motions. The response spectrum is expressed as the product of peak ground acceleration (PGA) and the normalized spectra (β = Sa/PGA) which can be smoothed by four spectral shape parameters. The proposed framework provides the expected median and covariance of the spectral shape parameters conditioned on specified design values of PGA and PGV/PGA (peak ground velocity/PGA). Efficient step-by-step procedures are developed for the application of the proposed alternative approach, and a sample application is illustrated and compared with the CS approach. It is demonstrated that the proposed methodology is capable of incorporating conventional probabilistic seismic hazard analysis (PSHA), considering spectral shape and spectral variability of realistic ground motions while avoiding the choice of the conditioning period. Site class effects can also be incorporated into the proposed approach.

Seismic retrofit of reinforced concrete shear walls using fibre reinforced polymer composites

This study studies seismic retrofitting of RC shear walls with externally linked aluminium tube polymers (CFRP). Three stages complete the research study. This method examined two eight-story CFRP-repaired RC shear walls. Excited walls were tested. The wall design was considered in NBC and CSA-A23.3–04. Throughout. The École polytechnique de Montréal's shake table simulated earthquakes to assess wall seismic resistance. Vibrations make the sixth panel more demanding and nonlinear. Panel six finished the tale. The earth's surface and twelfth-level walls were repaired and retested on a shaking table with varying ground motion excitation levels. Ground motion stirred the walls toward the end. Phase 2 involved the erection of three RC shear barriers. My college Structures Laboratory evaluated cyclic lateral stimulation panels. Evaluate the panel's performance. Two FRP panels and the control wall were tested. These panels were evaluated to determine the optimal method. All three ceiling tiles have code-designed parts, including the sixth-story stiffener panel. All building shear walls exceed construction criteria; hence, all wall panels have these features. These walls can handle the eight-story shear stresses. Continuous axial load, synchronized cyclic moment, and shear force were tested on the top panel. The panel could withstand all three forces. FRP retrofitting improved the wall panels' flexural and shear strengths. FRP retrofitting failed. Third, a computational macromodel simulated gripping and recycling wall panels under cyclic pressures. This simulation determined the longer-lasting wall panel type. Control wall panels were tested to discover whether they outperformed retrofitted ones. The two existing RC shear walls and three RC wall panels' FRP-retrofit schemes performed well and enhanced flexural strength, proving the retrofit's key aims. The quadratic numerical macromodel recreated monotonic and cyclic responses in wall panels under cyclic stresses. Nonlinear effects were accounted for using the nonlinear model.

Method for Determining Effective Frequency Range of Coherency Based on Seismic Energy

When using data recorded by dense instrument arrays to fit the coherency model of spatial variation of seismic ground motions, the selected frequency range may affect the fitting parameters, which also affects the synthesized time history of the ground motion field. In this study, the acceleration of the 5th and the 45th Earthquake of the SMART-1 array was selected. The Abrahamson and Loh models were used to perform the parameter fitting of the coherency for frequency ranges of 0–8, 0–16 and 0–24[Formula: see text]Hz, and the obtained results were different. The smaller the frequency range, the lower the fitted lagged coherency. The influence of frequency range on fitting parameters of Loh model is much greater than that of Abrahamson model. Based on the relative relationship of ground motion energy distribution in each frequency band represented by the power spectra, from the perspective of power spectrum energy, the energy ratio concept was introduced, i.e. the ratio of the power spectra for a specific frequency range to the total power spectra. Based on the energy ratio, a method for determining the effective frequency range of the coherency model was developed. Through the comparison and analysis of the horizontal-component acceleration of the SMART-1 array, it was found that when the frequency range was 0–5[Formula: see text]Hz, the energy ratio exceeded 95%, when the frequency range was 0–8[Formula: see text]Hz, the energy in the frequency band reached approximately 99% of the total energy. Therefore, it is recommended that when the parameters of the coherency model are fitted, the frequency corresponding to an energy ratio of 95% can be used as the effective frequency. Within this range, the contamination of high-frequency components on the fitting results is minimized.

Comparison of Nonergodic Ground-Motion Components from CyberShake and NGA-West2 Datasets in California

ABSTRACTIn this study, we compare the Southern California Earthquake Center CyberShake platform against the Next Generation Attenuation-West2 empirical datasets. Because the CyberShake and empirical datasets cover very different magnitude ranges and site conditions, we develop ground-motion models (GMMs) for CyberShake datasets to compare trends with empirical GMMs and decompose the residuals for further analysis. We apply mixed effects regression to four CyberShake datasets in southern, central, and northern California at 2, 3, 5, and 10 s periods, and compare the results with the empirical datasets using the same approach. CyberShake captures the total variability of ground motions in the empirical datasets but tends to predict larger median ground motions relative to the empirical GMMs. We then calculate and compare the repeatable source-specific location, site, and path effects between CyberShake and empirical datasets. We find that the correlations of site effects between the CyberShake and empirical datasets are generally satisfactory, but the variability of site effects is slightly smaller for CyberShake datasets. There is no apparent correlation of source-specific location effects between the CyberShake and empirical datasets. Comparison of path effects shows a wide range of correlation coefficients. Finally, we investigate the source of observed differences between the CyberShake and empirical datasets. We attribute the larger median ground-motion levels in CyberShake to a combination of the homogeneous slip patterns of the earthquake ruptures, the low resolution of near-surface materials in the velocity models, and strong reflections at high-contrast boundaries in the velocity models. These factors also impact the correlations of site and path effects between the CyberShake and empirical datasets. Moreover, the leakage from location effects into site and path terms further weakens the correlations. In summary, we find that CyberShake could be improved, but it is still very useful to supplement empirical datasets for ground-motion studies, especially to inform their nonergodic components.

Theoretical Solutions for Variable Ground Motions of Media-Transition Canyons with Partly Filled Water Subjected to SV-Waves Incidence

Long-span structures (e.g. dams or canyon-crossing bridges) are usually located at the sites with media transition, local topography and partially filled water. However, the existing studies on the spatially variable seismic motions considering local terrains mainly focus on the single- or dual-phase media with rare consideration of the effect of media transition. Therefore, this study is motivated to present and theoretically investigate the feature of seismic motions special for a media-transition canyon with partly filled water subjected to SV-wave excitation. First, the theoretical scheme for the media-transition site needs to simultaneously cope with the issue of wave propagation in single- and dual-phase media. The key step to connecting the two different types of wavefields lies in the satisfaction of boundary conditions along with the media-transition interface. Then, to further investigate the scattering effect caused by media transition on seismic motions under different angles and frequencies, a comparative study between the models with and without the media-transition interface is performed. Results show that the feature of media transition has noticeable influences on the spatially variable seismic motions. In addition, the effect of water depth on site response is analyzed in brief. Finally, the accuracy and reliability of the whole theoretical scheme are verified. The research provides useful insights that it is reasonable to introduce the media-transition factor into the study of spatially variable seismic motions.

Source parameter analysis using distributed acoustic sensing – an example with the PoroTomo array

SUMMARY In this study, I demonstrate that distributed acoustic sensing (DAS) raw strain rate data can directly be used to estimate spectral source parameters through an Empirical Green's Function (EGF) deconvolution analysis. Previously, DAS had been widely used in passive seismology to image the subsurface and analyze ground motion variations by converting strain or strain rate to particle velocity or acceleration prior to analysis. In this study, spectral analysis is applied to the PoroTomo joint DAS and seismic Nodal array in the Brady Hot Springs geothermal field to obtain source parameters for two M4 earthquakes via EGF analysis, where nearly collocated smaller events are used as an EGF to remove path and site effects. The EGF workflow is applied to raw DAS strain rate data without conversion to particle velocities and raw Nodal seismic data. The DAS and Nodal results are very consistent with similar features of spectral ratios, corner frequencies and moment ratios for the same event pairs. The uncertainty due to stacked spectral measurement is much lower on the DAS array, suggesting better stability of spectral shape measurement, possibly due to the much denser spatial sampling. The uncertainty due to model fitting is similar between DAS and Nodal arrays with slightly lower uncertainty on the DAS array. These observations demonstrate potential for directly using the strain rate measurements from DAS arrays for earthquake source characterizations.

Seismic hazard analysis of Silchar city located in North East India

North East India is a highly seismically active zone of India due to the collision tectonics between the Indian and the Eurasian plate in the north and subduction tectonics along the Indo-Myanmar range (IMR) in the east. It is utmost important to investigate the seismicity of this region along with uniform hazard spectra (UHS). In this paper, seismic hazard study has been performed at the Silchar district headquarters of Assam state, located in North East India. The earthquake data have been collected from various agencies from 1762 to 2020 and the fault data has been collected from seismotectonic atlas (SEISAT). Earthquake and fault data are superimposed on the Northeast India map using MapInfo software. The fault zone is defined based upon the earthquake’s density near the fault. Seismicity parameters and maximum magnitude have been estimated using Gutenberg-Richter (G-R) relationship. The best-fitted ground motion equation is considered. The outcome is represented in terms of controlling source, seismic hazard curve and UHS for Silchar city with varying ground motions. Finally, the results are presented as PGA based upon DSHA and PSHA methods. The effect of Importance Factor (I) and Response reduction factor (R) have been investigated by comparing UHS with IS: 1893-2016 code response spectra.

Spatial variation of strong ground motions in a heterogeneous soil site based on observation records from a dense array

The difference in local sediment thickness and soil properties has a significant impact on the spatial variation mechanism of seismic ground motion in the engineering scale. Due to the scarcity of observation data of dense arrays, the existing theoretical studies are mostly developed by numerical simulation methods, including human factors and a large number of assumptions. In view of this, based on the multistation observation records of the Luxian MS 6.0 earthquake and Yibin MS 5.1 earthquake obtained using a Zigong dense array, the study quantitatively analyzes the spatial characteristics of ground motion in heterogeneous soil sites by integrating a theoretical model with numerical analysis. In this study, many popular approaches including root-mean-square acceleration, horizontal-to-vertical spectral ratio (HVSR) of microtremor and strong motion records, and lagged coherency are comprehensively utilized to make the conclusion accurate and reliable. The results show that local soil conditions could affect the attenuation of coherence function with distance. The station-pairs with similar HVSR characteristics generally present a higher coherence level when the difference of the interstation distance is less than 100 m. In addition, the coherency function between stations will be greatly reduced when the H/V spectral ratio characteristics differ greatly, which is also obvious in the low-frequency part below 5 Hz. Finally, a lagged coherency model that considers the influence of heterogeneous soil is constructed in this study. The model has a definite physical meaning and can better represent the spatial variation of ground motion at nonbedrock sites.

Observations on the Seismic Loading of Rigid Inclusions based on 3D Numerical Simulations

Rigid inclusions are increasingly being specified in seismic regions to transmit foundation loads to competent strata at depth due to their ability to provide excellent static performance and potential for cost-savings over other forms of ground improvement and/or deep foundations. Despite their widespread application in seismic regions, the seismic kinematic interaction of rigid inclusions is not well understood. This study presents a series of parametric numerical simulations specifically conducted to capture the kinematic soil-rigid inclusion interaction under seismic loading to identify key mechanisms that contribute to seismic performance. The effect of ground motion variability, area replacement ratio, surface crust thickness, embedment into a competent layer, liquefiable layer thickness, and steel reinforcement is systematically investigated. Although the rigid inclusion may not prevent liquefaction triggering, severe amplification associated with dilation spiking of transiently liquefied soil is mitigated and the onset of liquefaction delayed due to the soil-rigid inclusion interaction. The role of static arching to alter the geostatic stress state prior to and during shaking is shown to be responsible for significant and heretofore unknown coupled fluid-mechanical interaction that drives the performance of the rigid inclusion within the reinforced soil system. The kinematic flexural demand following the triggering of liquefaction and phase transformation associated with cyclic mobility is met through transient increases in axial load, which increases the confinement of the grout comprising the rigid inclusion, and therefore its moment capacity. The complex mechanisms identified in this work should be used to help identify which subsurface conditions may lead to responses, guide design decisions regarding selection of reinforcement and embedment, and provide a basis for assessments of the anticipated kinematic demands in view of the beneficial axial load-moment capacity interaction following soil liquefaction.

MT-InSAR Unveils Dynamic Permafrost Disturbances in Hoh Xil (Kekexili) on the Tibetan Plateau Hinterland

Hoh Xil is an uninhabited extremity secluded on the Tibetan Plateau hinterland. A complete mapping of ground motion variation in Hoh Xil is essential for in-depth understanding of terrain’s responses to climate change on the Tibetan Plateau. However, the inaccessibility and extremely harsh environment impeded extensive field investigations on landform alteration and its formative process. Such difficulty can be resolved by Interferometric Synthetic Aperture Radar (InSAR), which enables a broad detection of subtle permafrost motions at millimeter precision. This study, for the first time, accomplished a Multi-temporal InSAR (MT-InSAR) deformation mapping from 2015 to 2020 in Hoh Xil, with a wide coverage of about 200,000 km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . 1,592 Sentinel-1 images were processed based on the small baseline subset (SBAS) technique. The results show that Hoh Xil was experiencing dynamic permafrost disturbances. Thawing permafrost with both the linear subsidence rate higher than 2 mm/yr and the periodic amplitude over 2 mm was primarily detected in areas of flat or gentle slopes. The InSAR cumulative deformation is highly correlated with permafrost thawing depth. Significant lag times were identified between seasonal oscillation of InSAR deformation and land surface temperature (LST). Thermokarst landforms of retrogressive thaw slumps and thermokarst lakes broadly formed and dynamically evolved as a consequence of permafrost degradation. Particularly, widespread thawing permafrost characterized by the spatial clustering of thermokarst lakes appeared to occur in areas adjacent to large lakes. The discovered dynamic permafrost disturbances in Hoh Xil manifested even the secluded Tibetan Plateau hinterland was facing the threat of climate change.

Influence of uncertainty of structural parameters on the stochastic dynamic response of asphaltic lining dam-foundation systems to non-stationary random seismic excitation

The present work aims toward the effect of uncertain structural parameters on the stochastic dynamic response of an asphaltic lining dam-foundation system subjected to stationary as well as non-stationary random excitation. Uncertain structural parameters of interest are shear modulus and mass density, modeled using the lognormal distribution. The stochastic seismic response of the dam-foundation system to the random loads with uncertain structural parameters is carried out with the Monte Carlo simulation method. The spatial variability of ground motion is considered with incoherence and wave passage effects as stationary as well as non-stationary random excitation. A time-dependent frequency response function is used throughout the study for non-stationary responses. Obtained results indicate that the variability of shear modulus and mass density can be neglected in stochastic dynamic analysis of an asphaltic lining dam-foundation system. Also, it is seen from the results that stationarity is a reasonable assumption for asphaltic lining dams to typical durations of strong shaking.

Seismic fragility analysis for subway station considering varying ground motion ensembles

The seismic fragility analysis involves employing an ensemble of ground motion records to establish the seismic performance. This paper investigates the effect of number of ground motion records in the considered ensemble on the calculated post-earthquake failure probability of subway structure. A two-dimensional (2D) finite element model was established considering the soil-subway station underground structure interaction. The cloud and incremental dynamical analysis (IDA) methods are employed to compute the seismic demand of the structure and the seismic fragility curves considering different ensembles of ground motion records. The results revealed that the number of records have a significant influence on the structure seismic fragility analysis in both cloud and IDA methods. It is suggested that the optimal ensemble size should comprise 300 ground motion records in the cloud-based seismic fragility analysis, and 24 ground motion records in the IDA method. The results also showed that the failure probability of structure predicted by the cloud method is greater than that predicted by the IDA method. These findings provide practical guidance for the performance-based seismic design of underground structures.

Influence of spatially varying ground motions on the seismic responses of bridge structures with KDampers

KDamper has been applied to control the seismic responses of bridge structures very recently. However, previous studies considered its performance under uniform ground motions only, the influence of the inevitable spatially varying ground motions (SVGMs) is not yet explored. To address this issue, this study systematically investigates the seismic responses of a large-span bridge structure equipped with KDampers subjected to SVGMs. In particular, the analytical model of a classical bridge equipped with KDampers is developed, and the corresponding dynamic equations of motion are formulated. Subsequently, KDampers are optimized by minimizing the mean peak response of the bridge deck in the frequency domain. Finally, parametric analyses are performed to comprehensively evaluate the influence of SVGMs (including wave passage and coherency loss effects) on the seismic responses of the bridge in both the frequency and time domains. The analytical results reveal that the optimized KDampers are effective in reducing the displacement and absolute acceleration responses of the bridge. Moreover, the effectiveness of KDampers is more evident when SVGMs are considered as compared to the uniform ground motions. This research can contribute to an in-depth understanding of the control effectiveness of KDampers, especially for the cases considering SVGMs.

Efficient simulation of stochastic seismic response of long-span bridges in river valleys using hybrid BEM-FEM

Determining ground motions is essential for seismic analysis of long-span bridges located at complex sites. However, there is a lack of earthquake records for local site conditions. Thus, this study focused on the effect of local site conditions on the stochastic response of long-span high-pier rigid frame bridges crossing a valley with an overlying water layer. For this purpose, a hybrid boundary element and finite element method (BEM-FEM) is proposed to investigate the stochastic seismic response of long-span bridges at such a complex site. First, a simulation method for 3-D spatially varying ground motions ascribed to wave scattering from irregular surface topography, sedimentary soil, and water layers was established based on the BEM combined with the spectral representation method. Furthermore, the statistical properties of the bridge response were explored based on the FEM and Monte Carlo simulations. The advantage of this work is that it reveals how the seismic wave propagation in this particular valley topography and water layer affects the stochastic response of the bridge considered. Moreover, the results indicate that seismic wave scattering leads to a significant energy redistribution of the input waves in the tri-directions related to the surface location, and a decrease in the coherency loss functions at all frequencies. Owing to this change, the peak ground accelerations (PGAs), bridge response means, and response variability are doubled. The beneficial effect of the water layer on the PGAs is weakened, while the adverse effect of hydrodynamic pressure dominates. The parameter analysis results demonstrate that a 10-m-deep sedimentary soil layer produces a 47% increase in the internal force of the pier bottom. The solid-liquid dynamic coupling effect should be accurately quantified for bridges located at saturated sites. Considering the local site conditions, the coefficient of variation (COV) of the response of the pier top exceeded 0.3, indicating strong randomness.

Dynamic Response of Deepwater Pile Foundation Bridge Piers under Current-wave and Earthquake Excitation

Pile foundation bridges are structures extending in the middle of the sea, so they are subject to currents, waves, and earthquake forces. This article presents a hybrid simulation that was used with input excitations of different current velocities, wave properties, and earthquake amplitudes to assess the non-linear dynamic behavior of pile foundation bridge piers. Based on the interface between MATLAB and ABAQUS software, the general formulations of fluid-structure interaction (FSI) under combined current-wave and earthquake loads are derived. Hydrodynamic and earthquake loading is consistently introduced by creating synthetic time histories of combined current-wave actions and spatially variable ground motion. The behavior of the dynamic model of a deepwater pile foundation bridge for the Songhua River in northeast China was adopted as an example of the study. The accuracy of the created model was verified using prior experimental and analytical computations. It is demonstrated how both linear and nonlinear dynamic behavior performs at various water depths under coupled current-wave-earthquake loading conditions. Revealing interesting aspects, particularly in terms of relative displacement, acceleration, shear, and moment response are shown. The results showed that the hybrid model is an efficient of simulating accurate predictions of the hydrodynamic pressure during earthquake actions for structures in coastal areas.