Field Ground Motion Research Articles

Seismic response of SMRFs retrofitted with bracing systems and nonlinear fluid viscous dampers under near and far field ground motion

Seismic response of SMRFs retrofitted with bracing systems and nonlinear fluid viscous dampers under near and far field ground motion

A new seismic wave input method for canyon sites based on the finite element method-indirect boundary integral equation method

The seismic input is the basis for the seismic safety analysis of dams, but current seismic input methods have not reasonably considered the influence of canyon scattering effects on the dynamic response of dams. In this paper, the total motion field of the canyon is deconstructed into the free field of a uniform half space and the scattering field of the canyon and they are obtained separately. The indirect boundary integral equation method (IBIEM) is used to determine the scattering field of the canyon, which is superimposed with the free field to obtain the seismic ground motion field (total motion field) of the canyon. The accuracy of the total motion field of the canyon is verified through reference solutions. In the finite element analysis of seismic ground motion field in the canyon, the total motion field at the truncation boundary of the canyon foundation is transformed into the equivalent seismic input loads and the interior of the canyon are simulated using the finite element method (FEM). Then, based on the wave input for the free field combined with the viscoelastic artificial boundary, a new wave input method for the total motion field combined with the viscoelastic artificial boundary is established. The seismic wave input method based on the finite element-indirect boundary integral equation method is applied to numerically determine the seismic response of a trapezoidal canyon. The differences in the seismic response of the canyon under free-field input and total motion field input are discussed. The results show that there is a certain deviation between the displacement and waveform obtained from the free-field input and the solutions obtained from the indirect boundary integral equation method. There is a large error for a large angle of incidence, and the errors increase with increasing seismic wave frequency. When the incident angle is 60°, the maximum error in the frequency domain reaches 92.3 %, and the maximum error in the time domain reaches 250 %. The displacement amplitude and waveform of the canyon obtained from the total motion field input showed agreement with the results of the indirect boundary integral equation method. The wave input method established in this paper has high calculation accuracy and reasonably considers the scattering effect of canyons, which provides a basis for more accurate predictions of the seismic response of dams on canyon foundations.

Study on train safety control of high-speed railway bridge under the action of near-fault earthquake

In order to study the effect of the velocity pulse on the dynamic response of the train-bridge system of the high-speed railway simple supported beam bridge, the velocity pulse is simulated by the trigonometric function method and superimposed with the far-field earthquake without pulse to synthesize the pulse with different pulse types, pulse periods and pulse peaks. A 10×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document}32m typical high-speed railway simple supported beam bridge is considered an case illustrating study. Then, the dynamic response of train-track-bridge coupling system is calculated by train-track-bridge seismic analysis software TTBSAS. Afterwards, the influence of pulse near-field earthquakes parameters and vertical components on dynamic response of train-bridge system and the safety of the train on the bridge are discussed in detail.The new derailment evaluation index is adopted to evaluate driving safety under earthquakes. The train safety control of simply supported beam bridge under the action of near-field earthquake is studied. The results show that the impact of pulse ground motion on the dynamic response of the train-track-bridge coupling system is significantly higher than that of no-pulse ground motion, especially the impact on the bridge and rail subsystem is more significant than that of train subsystem. Under the excitation of ground motion intensity of 0.05g∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document}0.15g, the safe speed threshold of pulse near-field ground motion is smaller than that of far-field ground motion. When the ground motion intensity is 0.20g∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document}0.30g, the safe speed threshold of pulse near-field ground motion and far field ground motion is 200km/h. So, the pulse near-field earthquake poses a greater threat to the safety of the train on the bridge than the far-field earthquake. Therefore, the influence of pulse near-field earthquakes should be considered in the seismic design. The research results of this paper can provide theoretitcal support for the design of a high-speed railway bridge in the near-field area.

The Behavior of Concrete Cantilever Retaining Walls During Far-Field and Near-Fault Earthquakes

Abstract The dynamic behavior of retaining walls is a complicated subject and a considerable design challenge, particularly under seismic conditions. Seismologists and investigators have an interest in near-fault earthquakes with significant velocity pulses because it can cause considerable displacements in constructions with respect to far-field earthquakes and consequently rise the hazard of earthquake-caused failure of structures. Despite there are several studies have investigated the seismic behavior of retaining structures, but the researches about retaining walls subjected to the influence of near fault like pulse earthquakes is still not adequate. The current study targets to numerically assess the dynamic performance of concrete cantilever retaining walls during far field ground motions (FFGMs) and near-fault ground motions (NFGMs). The nonlinear analysis of time history is conducted using the finite element method for three cantilever retaining wall models. The results of the analysis gained in terms of top horizontal displacement of the wall, active seismic earth pressure, and acceleration response of the system, which have been considered to recognize the impact of near fault earthquake on retaining structures. Additionally, the influence of different PGA of NF and FF earthquakes has been studied.

WITHDRAWAL – Administrative Duplicate Publication: From Source to Building Fragility: Post-event Assessment of the 2013 M7.1 Bohol Philippines Earthquake

We use ground motion simulations of the 2013 Bohol Philippines earthquake along with a new post-disaster exposure/damage database to constrain building fragility and vulnerability. The large number of damaged buildings (>70,000) and the wide spread of seismic intensities caused by this earthquake make it an ideal candidate for such a study. An extensive survey was conducted leading to a robust description of over 25,000 damaged and undamaged structures. Ground motion fields were simulated using ground motion prediction equations and stochastic modeling, and the estimated and observed values were compared. The finite source model used in the simulation was based on the analysis of aftershocks and SAR data. The ground motions were associated with the empirical database to derive fragility and vulnerability models. Results indicate that the pattern of damage is best captured in the stochastic simulation. Constraints were placed on seismic building fragility and vulnerability models, which can promote more effective implementation of construction regulations and practices.

A critical assessment of the design displacements of friction pendulum systems

The equivalent linear static procedure suggested in seismic codes for determining the maximum displacements of seismic isolation systems is evaluated comprehensively for friction pendulum isolators with respect to the benchmark nonlinear response history analysis procedure for a set of radii of curvature and coefficients of friction. A large set of selected and scaled near field ground motions recorded on stiff and soft soils are employed in comparative evaluations. It has been observed that equivalent linear static procedure significantly overestimates the maximum isolator displacements for all practical combinations of radius of curvature and friction coefficient. Overestimation is larger for ground motions on soft soils. Alternatively, a practical description of inelastic displacement spectra is introduced where the hazard is defined in terms of the 1-second spectral acceleration accounting for the seismicity and soil class of the site, and friction pendulum isolation systems are characterized by their radius of curvature and nominal friction coefficient. Employing the proposed design spectra in design and production may lead to significant reductions of the isolator sizes. Moreover, realistic estimation of maximum isolator displacements also leads to realistic estimation of isolator stiffness, as well as the internal design forces of both the isolation system and the superstructure through response spectrum analysis under design spectrum.

Deterministic full-scenario analysis for maximum credible earthquake hazards

Great earthquakes are one of the major threats to modern society due to their great destructive power and unpredictability. The maximum credible earthquake (MCE) for a specific fault, i.e., the largest magnitude earthquake that may occur there, has numerous potential scenarios with different source processes, making the future seismic hazard highly uncertain. We propose a full-scenario analysis method to evaluate the MCE hazards with deterministic broadband simulations of numerous scenarios. The full-scenario analysis is achieved by considering all uncertainties of potential future earthquakes with sufficient scenarios. Here we show an application of this method in the seismic hazard analysis for the Xiluodu dam in China by simulating 22,000,000 MCE scenarios in 0–10 Hz. The proposed method can provide arbitrary intensity measures, ground-motion time series, and spatial ground-motion fields for all hazard levels, which enables more realistic and accurate MCE hazard evaluations, and thus has great application potential in earthquake engineering.

Development of seismic fragilities for a base station steel lattice cellular tower

A large portion of the country of Turkey is located in a very high seismic region known as a first-degree earthquake zone where earthquakes occur frequently. Earthquakes result in damage to infrastructure including base station towers and subsequently failure of mobile communication networks. The loss of functionality of mobile communication networks following an earthquake has a direct impact on emergency response and both short and long-term recovery phases. Understanding both these phases requires systematic modeling of infrastructure components, which rely on fragility curves representing the probabilistic relationship between seismic intensity and damage. This study focuses on the development of damage fragility curves (fragilities) for an archetypical mobile cellular tower, namely a 55 m tall steel lattice tower (SLT) used in base station towers in Turkey. Nonlinear time history analysis was performed using a robust suite of far field ground motion records to model the performance of the archetype tower and develop damage fragilities for five specific damage states which were defined in terms of likely performance: damage state 0 (no damage), damage state 1 (uninterrupted communication), damage state 2 (communication interruption), damage state 3 (communication failure), damage state 4 (structural failure). While fragility curve has been developed for lattice towers of different types and sizes in the literature, there is no specific study for 55 m SLT and the novelty of this study is that the resulting SLT archetype fragilities can serve as a benchmark dataset for use in community-level risk and resilience analyses to improve response and recovery planning following earthquakes.

Seismic response of high-speed railway system under actions of ground motions from deterministic physics-based simulation

In order to investigate the response of a high-speed railway bridge under seismic excitations in the near-fault area, a deterministic physics-based method is used to construct the ground motion field in the near-fault area of a scenario earthquake. A finite element model of an assumed high-speed railway system is established, which consists of a finite length CRTS III ballastless track laid on a 15-span simply-supported girder bridge. The simulated ground motions and a group of three-component as-recorded accelerograms are used to provide non-uniform and uniform excitations at bridge piers, respectively. The seismic response of the rail-track-bridge system is calculated, and the effects of using different types of seismic excitations for the seismic analysis of the high-speed railway bridge in the near-fault area are analyzed. The results show that two end piers of a multi-span simply supported girder bridge could encounter remarkably different excitations in terms of waveform and frequency content for different bridge alignments in the near-fault area. The vertical response of the railway bridge system is more sensitive to the pattern of the excitation than the longitudinal response. Considering the spatial difference of ground motions among piers could increase the difference of the rail vertical displacement between the beam joint and mid-point of span, forming a remarkable periodic vertical irregularity of the rail. Using non-uniform excitation could lead to a reduction in DPeak and APeak which is most significant for DPeak in the vertical direction.

Shaking table test for near-valley subway station - Part I: Seismic site effects

As a typical local irregular topography, valley would have a significant influence on the seismic distribution around the local site as well as on seismic responses of near-valley underground structures, which has been evidenced by ground motion observation and field seismic records. However, current knowledge on the seismic site effects of the valley is limited to analytical solutions or numerical methods, and lack of experimental data from physical models. In this paper, a physical model test method based on 1g shaking table for arc-shaped valley topography is proposed, and a series of shaking table tests are carried out to investigate the seismic site effects induced by the valley topography. Details of experimental setup include not only the dynamic similitude design, the laminar model container and the model soil, but also the design and fabrication of arc-shaped valley topography with three kinds of depth-to-width ratios, i.e. 1/3, 1/4, and 1/8, as well as procedure for simulation of seismic excitations considering harmonic waves and actual seismic records. The free-field test case without valley site is also involved and taken as a benchmark comparison to better understand the seismic site effects of valley terrain. Acceleration sensors are placed and embedded in the model soil with different buried depths and distances to the local valley site in order to record the overall free-field seismic responses as well as the local topography effects. Results show that the dynamic response on the surface of model soil exhibits strong spatial variability due to the impact of the local valley topography. Results also indicate the ground acceleration increases within the local site, and the amplification effect is most pronounced at the valley top. The influence of the valley on the acceleration response of the ground is more significant when the predominant frequency of the seismic motions is higher and closer to the natural frequency of the site under different seismic motions. Furthermore, when the depth-to-width ratio of the valley increases, the acceleration amplitude at the valley top gradually increases, and the predominant frequency of Fourier spectrum at the valley top is also amplified. Notably, the Arias intensity amplification factor of the surrounding strata increases significantly due to the local valley topography, and the Arias intensity is also increased with the depth-to-width ratio of the valley.

Nonlinear seismic response analysis of reef-coral sand site in the South China Sea

To investigate the nonlinear seismic response of the reef-coral sand site in the South China Sea, a visco-elasto-plastic dynamic constitutive model and corresponding subroutine for coral sand material are developed in this study. The Matasovic skeleton curve and the derived hysteretic curve are refined in this model by introducing a critical shear modulus. Hysteresis criteria under irregular cyclic loads are established based on the improved Masing criteria. Moreover, increments of the octahedral strain and stress are utilized to construct the mapping rules between the three-dimensional stress-strain relationship and the one-dimensional stress-strain space. On that basis, a nonlinear finite element model of the reef-coral sand site is established, and the distribution pattern of the ground motion field and key ground motion parameters, such as the seismic amplification ratio and response spectrum of the reef-coral sand site, are investigated. The findings suggest that the coral sand layer significantly increases the site seismic responses, especially near the edge of the reef flat, thus posing a threat to the seismic safety of the buildings and construction in this area. Furthermore, the deformation of the reef-coral sand site tends to be concentrated on one side, resulting in a certain residual displacement after the earthquake.

A comparative study on the response of the L-shaped base isolated multi-storey building to near and far field earthquake ground motion

This study aims to understand the behaviour of a base isolated l-shaped building under far field and near field earthquake ground motion. A ten-storey l-shaped building was considered for the study and modelled using SAP2000, which is finite-element-based software. At first, a non-isolated model was created, and the required data was generated in order to develop an isolated model. After that, a non-linear time history analysis was performed, and the results of storey displacement, torsional irregularity, and base shear have been discussed for the base isolated model and the non-isolated model. The fundamental time period of base isolated l-shaped building was found to be 2.56 s while the base model had fundamental time period of 0.88 s. It was found in this study that higher peak ground acceleration (PGA) and peak ground velocity (PGV) of the ground motion led to higher storey displacement, storey drift, and base shear but a lower torsional irregularity ratio under near field ground motion, while torsional irregularity ratio of base isolated building was found to be increased under far field ground motion.

The Effect of Soil Characteristics On NFGM and FFGM Ground Motion Response Spectra

This study aims to achieve the following goals: 1- To distinguish between the inelastic responses of buildings under earthquakes with NFGM and FFGM. 2- To inspect the effect of soil shear velocity on the response spectra. Several earthquake events, with different characteristics, are brought from the PEER website for “Pacific Earthquake Engineering Research” and analyzed using PRISM software to achieve these goals. The research found that the acceleration, velocity, and displacement response of the selected near-fault ground motions on the structure has a higher effect than the far- field ground motion response in both types of soils and this difference is displayed more noticeably in long periods (periods after 0.2 sec). And when comparing responses of the two types of soils (the soft soil type and the rock type) it shows that the geological and geotechnical aspects of the soil deposits majorly affect the response spectra of the free field surface motions

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.

A Fourier series non-stationary coherency model with respect to site conditions for the horizontal component of ground motion

A Fourier series non-stationary coherency model with respect to the site conditions for the horizontal component was developed. The evolution of the model was achieved using parameters related to the site, inter-station distance, and time. First, based on the simulation of a non-stationary ground-motion field considering the wave-passage effect and site-response effect, the approach used for the estimation of coherency using wavelet transform is presented. Subsequently, the Fourier series non-stationary coherency model is formulated. The parameters are considered piecewise constant variables to represent the non-stationarity of the estimated coherency. The effects of the site and inter-station distance on the proposed model are presented. Parameters related to the site and inter-station distance were obtained. Finally, the proposed model is compared with the ground motion records at the SMART-1 array during Event 45, the stationary model, and the data from the Argostoli rock-site dense array. This indicates that the Fourier series non-stationary coherency model with respect to site conditions for the horizontal component can well match the correlation of the realistic spatially variable seismic ground motion, which is related to the site, time, and inter-station distance.

Probabilistic seismic assessment of innovative concrete bridge piers with Engineered Cementitious Composites (ECC) by different types of shape memory alloys (SMAs) bars

Critical role of bridges in post-earthquake rescue activities has made their seismic safety a major concern of structural engineers. While preventing collapse is one of essential requirements in bridge engineering, recent earthquakes have shown that bridges may also cease functionality due to residual deformations. To address this, shape memory alloys (SMAs) have received wide attentions according to their ability to recover the initial shape even after large plastic deformations. Two types of SMAs (NiTi and Cu–Al–Mn) are used in this paper to reinforce nine different concrete bridge piers in which Engineered Cementitious Composite (ECC) is also used for enhancing ductility in plastic hinge region. Each of the piers is subjected to 56 near field ground motions and collapse capacity of the piers is evaluated probabilistically using incremental dynamic analysis. The comparative results indicate that simultaneous use of steel and NiTi reinforcement in a plastic hinge area filled with ECC concrete can lead to a 30% improvement in median collapse capacity of the studied pier.

A probabilistic framework for the stability analysis of slopes considering the coupling influence of random ground motion and conditional random field

The uncertainty of the input parameters can have a significant influence on the evaluation of the slope stability. A simple probabilistic framework is presented in this paper to quantify the influence of the uncertainties of the stochastic ground motion coupled with the spatial variability of soil parameters. The robust quasi–Monte Carlo simulation in the proposed framework is employed to estimate the failure probability of slopes. The conditional random field (CRF) is manipulated to simulate the spatial variability of soil properties with the sample points where the soil parameters are determined, and the spectral representation of stochastic process is applied to generate the horizontal and vertical stochastic ground motions. In each run of the Quasi–Monte Carlo simulation, a modified Newmark method based on an infinite slope failure model is applied to determine the permanent displacement of slopes under horizontal and vertical ground motions. The originality and significance of this proposed probabilistic framework are validated by a real slope case. The results of the case show that the uncertainty affecting the stability of the slope can decrease when CRF is used in a random field simulation to incorporate the real values of soil parameters at sample points, and the failure probability of slopes can be underestimated without considering stochastic vertical ground motion. Moreover, the correlated distance and critical permanent displacement are significant in predicting the failure probability of slopes.

Seismic Structure-Soil-Structure Interaction between a pair of buildings with consideration of rotational ground motions effects

During an earthquake, buildings are analysed dynamically without any consideration of their neighbouring structures and usually this also neglects the influence of surficial rotational ground motion. Population growth and increased land costs have increased the spatial density of buildings in urban areas. This closer proximity of buildings to one another leads to more complex interactions between buildings and the surficial seismic ground motion field that includes both horizontal and rotational components. To address these issues, this paper explores the Structure-Soil-Structure Interaction (SSSI) between a pair of buildings, including the surficial horizontal and rotational ground motions. A reduced-order parametric model of this complex system is proposed. Ground accelerogram data recorded from the 6-DOF sensor SINAPS@ Kefalonia (Greece) post-seismic experiment and the SMART-1 array in Taiwan were employed. This extensive parametric study analyses over six million system/ground motion cases. Results suggest that the rotational ground motion can affect the seismic response when the SSSI is considered, producing an additional amplification of acceleration responses of certain structures. The impact of the rotational ground motion depends principally on the fundamental natural period of the building, and the SSSI depends mainly on the frequency ratio (here Ωb) between the buildings.

A cost-benefit analysis of sensor quality and spatial density for rapid regional post-event seismic damage assessment: Application to Istanbul

A quantitative evaluation of the influence of sensor quality and spatial density on the results of rapid regional seismic damage evaluations of buildings can provide an important reference for the deployment of a strong-motion network. However, the influence of sensor quality and spatial density on seismic damage assessment is still unclear. Therefore, a cost-benefit analysis framework of sensor quality and spatial density for rapid regional post-event seismic damage assessment is proposed. In this framework, a simulation method for sensor-recorded ground motions and an interpolation-based ground motion field refinement method are used to consider the influence of the quality and density of the sensor network. The accuracies of seismic damage assessments with different sensor layout schemes were compared using the time-history analysis-based regional seismic damage assessment method, through which the influence of sensor quality and spatial density on the seismic damage assessment can be quantitatively evaluated. Finally, the Zeytinburnu district of Istanbul was selected as an example for illustrating the proposed framework. The main conclusions are as follows: (1) the spatial density of the sensors used is more significant for improving the accuracy of a seismic damage assessment than the quality of the sensors used; (2) the influence of population density can be considered using the proposed framework; and (3) the proposed framework can quantitatively consider the influence of sensor quality and spatial density on the rapid regional seismic damage assessment of buildings, which provides an important reference for the deployment of a strong-motion network for a given budget.

Experimental investigation of seismic performance of shield tunnel under near-field ground motion

The near-field ground motion is one of the challenges to underground structure in soft soil site. In order to study seismic performance of shield tunnel under near-field ground motion, a series of large-scale shaking table tests are conducted. A refined tunnel lining is developed to capture the extension/closure response of joints. The difference of seismic response of shield tunnel under near field ground and far field ground motion is compared and analyzed. The findings show that compared with far-field ground motion, the acceleration response of segmental lining, cross-sectional deformation, extension/closure of longitudinal joints, dynamic normal earth pressure, and strain on segmental lining are increased obviously under the action of near-field ground motion. The near-field ground motion significantly stimulates the response of the tunnel structure in a wider low frequency range. The adverse effect of near-field ground motion on shield tunnel in soft soil site is significantly greater than that of far-field ground motion.