Pacific Earthquake Engineering Research Center Research Articles

Nonlinear seismic analysis of RC framed structures with horizontal and vertical base-isolation

The ratio of the vertical-to-horizontal peak ground accelerations highlights the fact that values greater than one tend to occur in the near-fault area, where the corresponding ratio of spectral accelerations may be amplified in the range of low vibration periods. The high vertical-to-horizontal stiffness of a base-isolation system (e.g. high-damping-rubber bearings, HDRBs) of a reinforced concrete (RC) framed structure causes the superstructure to behave like a fixed-base one in the vertical direction. Seismic damage induced by vertical excitation is generally located at the upper storeys, where the effects of gravity loads generally prevail over those of the horizontal loads and an amplification of the vertical motion is expected. In the present work, attention is focused on the combination of horizontal and vertical base-isolation resulting from the in-series vertical arrangement of a HDRB and a HDR layer, the latter not affecting the horizontal stiffness of the isolator but reducing its vertical stiffness. The main objective is to evaluate the isolation ratio in the vertical direction that needs to be considered for effective protection against significant vertical component of near-fault earthquakes. A five-storey RC framed structure is first designed as fixed-base in a medium-risk zone, in compliance with a former Italian seismic code. It is retrofitted by the insertion of a horizontal-vertical base-isolation system, with nominal, upper-bound, lower-bound and mixed design properties defined by current European seismic codes. Nonlinear seismic analysis of the test structures is carried out with reference to near-fault earthquakes selected from the Pacific Earthquake Engineering Research Center database and scaled to match the design spectrum of acceleration. Finally, the vertical stiffness to be assigned to the isolation system to obtain a shift from the vibration periods of maximum amplification is evaluated by wavelet analysis, including the moving resonance effect induced by inelastic deformation of the superstructure.

An innovative framework for risk assessment of non-structural components for industrial plants

Na-Tech events (Natural Hazard Triggering Technological Disasters) are industrial accidents triggered by natural events such as hurricanes, floods, earthquakes, tsunami, etc. In the recent decades, various analytical approaches for the performance-based earthquake engineering (PBEE) have been developed. The most famous approach has been provided by the Pacific Earthquake Engineering Research (PEER) Center, which consists of four stages: hazard analysis, demand analysis, damage analysis, and risk assessment. The accuracy of this method in the case of complex critical infrastructure, such as nuclear and non-nuclear industrial plants, is still under investigation. Specifically for these critical structures, it is necessary to define different Limit States and appropriate Engineering Demand Parameters (EDP), especially in presence of critical Non-Structural Components (NSC), whose damage can have serious consequences. Furthermore, because of the narrow distribution of frequencies in the demand of NSC, the selection of ground motion records for fragility analysis is also a critical aspect. Consequently, the aim of the proposed study is to investigate the suitability of the PBEE approach in presence of NSCs and their dynamic interaction with the primary structure. On these premises, a comprehensive shake table test campaign was carried out with the aim to investigate the seismic behaviour of two structural configurations of a representative industrial multi-storey frame equipped with process NSCs. The main limit states for NCSs are identified and the related fragility curves are built, in a PBEE perspective, based on both experimental results and finite element model (FEM) simulations. For this purpose, an innovative algorithm for ground accelerogram selection is used. Finally, the mean annual frequency (MAF) of exceedance of the experimentally identified limit states for relevant NSCs is carried out.

Comparison of the simulated seismic behavior of small- and large-scale cripple walls: PEER-CEA Project test programs

As part of the Pacific Earthquake Engineering Research Center (PEER)-California Earthquake Authority (CEA) project, experimental programs were performed at UC San Diego and UC Berkeley, with the former focusing on small-component testing and the latter focusing on large-component testing. During the small-component testing program, a suite of 28 cripple wall-only specimens was tested under quasi-static reverse cyclic lateral loading with variations in exterior finishes, retrofit condition, cripple wall height, anchorage condition, boundary conditions, vertical load, and loading protocol. In the large-component testing program, cripple wall-first story specimens, load path connections, and combined materials in occupied stories were tested. The more easily performed small-component specimens facilitate comparison with the large-component specimens to allow the assessment of their potential to emulate large-scale specimen behavior, with a particular interest in cross-comparing their global hysteresis and physical damage evolution. This cross-comparison among small- and large-scale specimen test results is intended to offer best practices for the future design of cripple wall seismic retrofits in residential housing, with a particular interest in: (1) supporting the realistic design of small-component specimens that may capture the response of large-component specimens and (2) to qualitatively determine where the small-component tests fall in the range of lower- to upper-bound estimation of strength and deformation capacity for the purposes of numerical modeling. Data from both test programs were utilized in the PEER-CEA project to assist with validating numerical modeling tools, which in turn were used to generate seismic loss models capable of quantifying the reduction of loss achieved by applying state-of-practice retrofit methods as identified in FEMA P-1100 Vulnerability-Base Seismic Assessment and Retrofit of One- and Two-Family Dwellings. The objective of this article is to present an overview of the small- and large-component testing programs and key results pertaining to exterior finishes, boundary conditions, the FEMA P-1100 retrofit, and cripple wall height.

Fuzzy optimization for ground motion intensity measures to characterize the response of the pile-supported wharf in liquefiable soils

In the Performance-Based Earthquake Engineering (PBEE) framework of Pacific Earthquake Engineering Research (PEER) Center, the structural seismic responses are usually expressed by probabilistic seismic demand models (PSDMs), which provide a representative relation between ground motion intensity measures (IMs) and engineering demand parameters (EDPs). Since the degree of uncertainty of PSDMs is dependent on the IMs used, the selection of optimal IM is very beneficial to enhance the credibility and ultimately contributes to a reliable decision. PSDMs and the fuzzy comprehensive evaluation method are used to select the most optimal IM for the pile-supported wharf in liquefiable soils in this study. The finite element model is calibrated first to verify the model validation. Furthermore, 100 real ground motions are applied to the calibrated model as earthquake inputs. Four parameters are used as the pile-supported wharf EDPs. A total of 30 groups of IMs are evaluated from five aspects as practicality, efficiency, proficiency, sufficiency, and hazard computability. Finally, the optimal set of IMs for different EDPs with the fuzzy decision matrix are determined by the fuzzy comprehensive evaluation method.

A Deep Learning-Based Approach for the Identification of a Multi-Parameter BWBN Model

A restoring-force model is a versatile mathematical model that can describe the relationship between the restoring force and the deformation obtained from a large number of experiments. Over the past few decades, a large body of work on the development of restoring-force models has been reported in the literature. Under high intensity cyclic loadings or seismic excitations, reinforced concrete (RC) structures undergo a wide range of hysteretic deteriorations such as strength, stiffness and pinching degradations. These characteristic behaviors can be described by the multi-parameter Bouc-Wen-Baber-Noori (BWBN) model, which offers a wide range of applicability. This model has been applied for the response prediction and modeling restoring-force behavior in structural and mechanical engineering systems, by adjusting the distribution range of this model’s parameters. However, a major difficulty in utilizing the multi-parameter BWBN model is the parameters’ identification. In this paper, a deep neural network model is used to estimate the hysteresis parameters of the BWBN model. This model is one of the most versatile and widely used general hysteresis models that can describe the hysteretic behavior of RC columns. The experimental data of the RC columns used in this paper are collected from the database of the Pacific Earthquake Engineering Research Center (PEER). Firstly, the hysteretic loop obtained from a physical experiment is described by the BWBN model, and the parameters of the BWBN model are identified via a genetic optimization algorithm. Then a neural network is established by a backpropagation (BP) algorithm for associating the identified BWBN model parameters with physical parameters of the RC column. Finally, the regression analysis of the identified parameters is carried out to obtain the regression characteristics of the RC columns. The trained neural network model can directly identify the parameters of BWBN model based on the physical parameters of RC columns, and is effective and computationally efficient for multi-parameter BWBN model identification. The proposed approach overcomes the difficult problem of identifying the parameters of BWBN model and provides a promising approach for a wider application of this multi-parameter hysteresis model.

Summary of the Abrahamson and Gulerce NGA-SUB ground-motion model for subduction earthquakes

A set of region-specific ground-motion models (GMMs) for subduction zone earthquakes are developed based on the database compiled by the Pacific Earthquake Engineering Research Center (PEER) Next Generation Attenuation: Subduction project (NGA-SUB). The subset used to develop the GMMs includes 3914 recordings from 113 subduction interface earthquakes with magnitudes between 5 and 9.2 and 4850 recordings from 89 intraslab events with magnitudes between 5 and 7.8. The functional form of the global GMM accommodates the differences in the magnitude, distance, and depth scaling for interface and intraslab earthquakes. In addition to the global model, region-specific GMMs are developed for seven regions: Alaska, Cascadia, Central America, Japan, New Zealand, South America, and Taiwan. The magnitude scaling and the geometrical spreading parameters of the global model are used in all region-specific models, with the exception of the Taiwan region, which has a region-specific geometrical-spreading term. Four region-specific terms are included in the median GMM: the large distance (linear R) scaling, linear site amplification scaling (ln(VS30)), basin depth scaling (for Cascadia and Japan), and the constant term. The aleatory variability is also regionalized with larger aleatory variability at short periods for the Central America, Japan, and South America regions. Estimates of the epistemic uncertainty for the median and aleatory terms for each region are provided. The proposed global and region-specific GMMs are considered to be applicable to sites in the forearc region at distances up to 500 km, magnitudes of 5.0–9.5, and spectral periods from 0 to 10 s. The Cascadia-specific model is applicable to distances of 800 km including the backarc region.

Study of the Target Earthquake-Induced Track Irregularity Spectrum under Transverse Random Earthquakes

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

An improved variational mode decomposition for seismic random noise attenuation using grasshopper optimization via shape dynamic time warping

In seismic signal processing, attenuation of noise is one of the most difficult challenges. Variational mode decomposition (VMD) is a recently developed adaptable signal processing technique that subdivides a signal into bandlimited intrinsic mode functions (BIMFs). In VMD, the key elements are the number of intrinsic modes and the quadratic penalty factor for better denoising. In this paper, we have applied the Grasshopper optimization algorithm (GOA) to determine the key elements of VMD and decomposes the signal into optimized BIMFs. Then, the Shape dynamic time warping (shapeDTW) is applied for determining the relevant modes. Finally, the relevant modes are deal with Wavelet thresholding (WT) to obtain a better result of signal to noise ratio (SNR). Initially, the analysis is made on the synthetic signals to represent the dominance of the new approaching method with Empirical mode decomposition (EMD) based and VMD based methods. We also applied new approaching method to a 1D real seismic signal from the Pacific Earthquake Engineering Research Center (PEER) ground motion database to suppress the random noise interferences. The proposed approach is also tested in a 2D synthetic seismic section corrupted by random noise, and also with a 2D real Forrest seismic survey in South Australia's resources information gateway. Application of the proposed GOA-VMD-shapeDTW-WT method on both the synthetic and the real seismic signal shows supremacy with other denoising techniques.

Failure Mode and Optimization for MSCSS with LRBs Based on IDA Method

The mega-sub controlled structure system with laminate rubber bearings is an emerging seismic control system for high-rise buildings. The system is high-order statically indeterminate with numerous failure modes. To study the failure modes of the structural system and further improve its seismic performance, the dynamic equations and the finite element model of the system were established. Ten different ground motions were selected from the Pacific Earthquake Engineering Research Center ground motion database for the incremental dynamic analysis (IDA). Based on the results of the IDA, the weakest failure mode of the system was identified, and its failure path was found. Two schemes were proposed to optimize the weakest failure mode of the system, and the optimization results were compared. The results show that although the IDA curves from different ground motion inputs are diverse, the plastic hinges are all formed on the sub-structures. Failures of the system are caused by either the excessive floor drift or the excessive shear deformation of rubber bearings. By adjusting the locations and parameters of dampers and rubber bearings, the seismic performance of the system can be improved.

Dynamic Responses of Liquid Storage Tank Under Near Fault Pulse-Like Earthquakes With Different Focal Mechanisms

A liquid storage tank has a very extensive role in the petrochemical industry, and earthquake damage will cause very serious consequences. Considering the fluid-solid coupling, material nonlinearity and liquid level shaking dynamic behavior, three-dimensional calculation models of non-isolated and isolated liquid storage tanks are established, respectively. 12 earthquake waves are selected from Pacific Earthquake Engineering Research Center (PEER), and there are three earthquake waves of reverse (R), strike slip (SS), reverse oblique (RO) and normal (N) focal mechanisms, respectively. The influence of the focal mechanism on the dynamic responses of the liquid storage tank is investigated. The effectiveness control of sliding isolation on a near fault earthquake is discussed. The influence of the diameter of the limiting device on the shock absorption effect is analyzed. The results show that the order of influence of four types of focal mechanisms on liquid sloshing wave height is as follows: RO$mathrm{>$R$mathrm{>$SS$mathrm{>$N. For the wall displacement, liquid pressure and effective stress of the tank wall, the response under N-type focal mechanism earthquake is generally larger than that of the other three types, and the difference of wall displacement, liquid pressure and wall effective stress under RO, R and SS focal mechanism earthquakes is small. The results show that the dynamic responses of the liquid storage tank under different focal mechanism earthquakes is quite different. Sliding isolation can significantly reduce the dynamic responses of the liquid storage tank under strong near-fault earthquakes, and the diameter of the limiting device will affect the shock absorption effect of sliding isolation.

Distributed Fiber-Optic Strain Sensing of an Innovative Reinforced Concrete Beam-Column Connection.

Distributed fiber-optic sensing (DFOS) technologies have been used for decades to detect damage in infrastructure. One recent DFOS technology, Optical Frequency Domain Reflectometry (OFDR), has attracted attention from the structural engineering community because its high spatial resolution and refined accuracy could enable new monitoring possibilities and new insight regarding the behavior of reinforced concrete (RC) structures. The current research project explores the ability and potential of OFDR to measure distributed strain in RC structures through laboratory tests on an innovative beam–column connection, in which a partial slot joint was introduced between the beam and the column to control damage. In the test specimen, fiber-optic cables were embedded in both the steel reinforcement and concrete. The specimen was tested under quasi-static cyclic loading with increasing displacement demand at the structural laboratory of the Pacific Earthquake Engineering Research (PEER) Center of UC Berkeley. Different types of fiber-optic cables were embedded both in the concrete and the rebar. The influence of the cable coating and cable position are discussed. The DFOS results are compared with traditional measurements (DIC and LVDT). The high resolution of DFOS at small deformations provides new insights regarding the mechanical behavior of the slotted RC beam–column connection, including direct measurement of beam curvature, rebar deformation, and slot opening and closing. A major contribution of this work is the quantification of the performance and limitations of the DFOS system under large cyclic strains. Performance is quantified in terms of non-valid points (which occur in large strains when the DFOS analyzer does not return a strain value), maximum strain that can be reliably measured, crack width that causes cable rupture, and the effect of the cable coating on the measurements. Structural damage indices are also proposed based on the DFOS results. These damage indices correlate reasonably well with the maximum sustained drift, indicating the potential of using DFOS for RC structural damage assessment. The experimental data set is made publicly available.

Development of NGA-Sub ground-motion prediction equation of 5%-damped pseudo-spectral acceleration based on database of subduction earthquakes in Japan

We developed an empirical ground-motion model for subduction earthquakes in Japan. The model is based on the extensive, comprehensive subduction database for Japan by the Pacific Earthquake Engineering Research Center. The model predicts the RotD50 horizontal components of peak ground acceleration, peak ground velocity, and 5%-damped elastic pseudo-spectral acceleration ordinates in the selected periods ranging from 0.01 to 10 s. The model includes predictor variables considering tectonic setting (i.e. interplate and intraplate), the hypocentral depths, magnitude scaling, distance attenuation, shallow soil, and the basin responses. The magnitude scaling of interplate earthquakes is well constrained in Japan for different periods because the database includes the well-recorded large-magnitude events (i.e. the 2003 Tokachi-Oki and 2011 Tohoku earthquakes). The developed ground-motion prediction equation covers the subduction earthquakes that occurred in Japan for moment magnitudes ranging from 5.5 to 9.1 with closest distances to the fault of less than 300 km.

Wavelet-Based Stochastic Model for Jointly Simulating Three-Component Ground Motions

ABSTRACTA large number of ground motions are needed in performance-based earthquake engineering. To date, most existing stochastic models are limited to simulating a single horizontal component of earthquake motions. This study proposes a wavelet-based stochastic method for jointly simulating three-component accelerograms using earthquake magnitudes, source-to-site distances, and site conditions as input. Based on the Pacific Earthquake Engineering Research Center Next Generation Attenuation (NGA)-West2 database, prediction equations are developed for wavelet-packet parameters of two horizontal and one vertical components. Correlations among these components are obtained to jointly simulate three-component motions based on earthquake scenarios. The simulated ground motions are systematically compared with existing ground-motion attenuation equations. The model has the capability to simulate the different frequency content of horizontal and vertical motions. The simulated vertical-to-horizontal spectral ratios are found to be consistent with observed strong-motion data. The model is applicable to shallow crustal earthquakes in an active tectonic region with a moment magnitude between 5 and 8, source-to-site distance from 0 to 100 km, and shear-wave velocity in the top 30 m (VS30) in the range of 150–1000 m/s. It can find important applications in 3D time-history analyses in performance-based earthquake engineering.

Fragility-based seismic performance assessment of modular underground arch bridges

Seismic performance assessment of modular underground arch bridges (MUABs) can help mitigate structural damage to MUABs during earthquakes. This study proposed an efficient procedure to evaluate the seismic performance of a three-hinge MUAB by using fragility-based analysis. Firstly, a novel proposal for damage states was presented using the relationship between the crack depth and thickness of the arch component. The relationship between ground motion intensity and structural failure probability was then described using stratum-uncertainty characteristics. The multiple stripe analysis approach with the maximum likelihood function was introduced to detail the uncertainty characteristics of strata by allowing various ground motions at distinct seismic intensity levels. Finally, the collapse probability considering stratum-uncertainty characteristics was specified for seismic intensity and probability levels. The results revealed that the proposed procedure to randomly select ground motions from the strong-motion database of the Pacific Earthquake Engineering Research Center is feasible for evaluating the seismic vulnerability of MUABs. Therefore, the seismic performance of MUABs can be reasonably predicted under earthquakes.

Site-Specific Ground Response Analysis using the Geotechnical Dataset in Moderate Seismicity Region

An understanding of the soil response to dynamic waves from the earthquakes is an important aspect of engineering safety measures against tremors. This research presents the equivalent linear site response analysis of the Miri district by using a geotechnical dataset. The main objective of this paper is to study the amplification factor for the district of Miri. Analysis of site response is critical in determining the earthquake risk and harm allocation during earthquakes. The standard penetration test ‘N’ value (SPT-N) has been used in this study. A specific soil-type relationship has been used between shear wave velocity and SPT-N value to produce profiles of shear wave velocity in each borehole site in the Miri district. For all SPT-N borehole sites, site response parameters were interpolated to produce site response maps and shear wave velocity maps in the geographical information system (GIS) environment. The research showed that the Malaysian national annex to Eurocode 8 (MNA-EC8) site class C, D and E are dominant in the Miri district. Due to the inadequacy of records of input ground motions of low-to-moderate seismicity regions, this research used an earthquake record from other locations well-matched from a target response spectrum with similar characteristics obtained from the Pacific Earthquake Engineering Research Center (PEER) online database (PEER NGA). The equivalent linear method (EQL) using DEEPSOIL is an extensively researched numeric technique that is used for assessment of site response. From the results, it has been found that the amplification ratio varies from 2.1 to 4.79 and it suggests that it is vital to study the site effect in the seismic hazard assessment of the Miri district. The work also emphasizes the relationship between seismic microzonation and site response analysis in order to reduce the adverse effects of earthquakes in Miri city by planning a proper land use.

Predicting the Lateral Load Carrying Capacity of Reinforced Concrete Rectangular Columns: Gene Expression Programming.

This research presents a novel approach of artificial intelligence (AI) based gene expression programming (GEP) for predicting the lateral load carrying capacity of RC rectangular columns when subjected to earthquake loading. To achieve the desired research objective, an experimental database assembled by the Pacific Earthquake Engineering Research (PEER) center consisting of 250 cyclic tested samples of RC rectangular columns was employed. Seven input variables of these column samples were utilized to develop the coveted analytical models against the established capacity outputs. The selection of these input variables was based on the linear regression and cosine amplitude method. Based on the GEP modelling results, two analytical models were proposed for computing the flexural and shear capacity of RC rectangular columns. The performance of both these models was evaluated based on the four key fitness indicators, i.e., coefficient of determination (R2), root mean squared error (RMSE), mean absolute error (MAE), and root relative squared error (RRSE). From the performance evaluation results of these models, R2, RMSE, MAE, and RRSE were found to be 0.96, 53.41, 38.12, and 0.20, respectively, for the flexural capacity model, and 0.95, 39.47, 28.77, and 0.22, respectively, for the shear capacity model. In addition to these fitness criteria, the performance of the proposed models was also assessed by making a comparison with the American design code of concrete structures ACI 318-19. The ACI model reported R2, RMSE, MAE, and RRSE to be 0.88, 101.86, 51.74, and 0.39, respectively, for flexural capacity, and 0.87, 238.74, 183.66, and 1.35, respectively, for shear capacity outputs. The comparison depicted a better performance and higher accuracy of the proposed models as compared to that of ACI 318-19.

New conditional, scenario-based, and traditional peak ground velocity models for interface and intraslab subduction zone earthquakes

The Pacific Earthquake Engineering Research (PEER) Center next-generation attenuation relationships for subduction zone earthquakes (NGA-Sub) ground motion database is used to develop new conditional ground motion models (CGMMs), several scenario-based ground motion models (GMMs), and a traditional GMM to estimate the peak ground velocity ( PGV) for subduction zone (interface, intraslab) earthquakes. The PGV estimate in the CGMMs is conditioned on the rupture distance ( Rrup), magnitude ( Mw), time-averaged shear wave velocity in the top 30 m ( V s30) and pseudo-spectral acceleration PSA( T PGV). The period T PGV in the CGMMs is magnitude dependent to account for the magnitude dependence of the earthquake source corner frequency in the Fourier amplitude spectrum. Several scenario-based models are developed by combining the CGMM with PSA GMMs to directly estimate PGV given an earthquake scenario and site condition. Scenario-based models capture the complex ground motion effects in the underlying PSA GMMs and ensure the consistency with a design PSA spectrum, which is desired in engineering practice. In addition, a traditional PGV GMM is developed using Bayesian hierarchical regression. Finally, we compare all of these models and find that the scenario-based models are consistent with the traditional model developed in this study giving confidence to their use. The conditional and traditional PGV GMMs developed in this study benefit the performance-based design of engineering systems affected by subduction earthquakes when PGV is an important intensity measure.

A boundary element approach for the evaluation of SSI effects in presence of pile foundations under steady-state conditions

Simplified procedures, capable of predicting the main effects of soil-structure interaction (SSI), involving minimum computational effort are desired in engineering practice. Besides, user-friendly approaches can be incorporated into guidelines or practical recommended procedures. Nevertheless, approximate solutions need to be carefully validated through rigorous analytical or numerical methods, as well as by the comparison with experimental results or field measurements. In the case of piles, the flexibility of the soil-foundation system plays a fundamental role in structural design and the evaluation of the pile group effects still represents a crucial task in practical problem. In this paper, a Boundary Element approach based on the Stiffness Matrix Method (Kausel in Fundamental solutions in elastodynamics. A compendium, Cambridge University Press, England, 2006) is employed to investigate the key features of SSI, by comparison with the actual field data collected by Stewart et al. (Empirical evaluation of inertial soil-structure interaction effects. Rep. No. PEER-98/07, Pacific Earthquake Engineering Research Center, 1998) from instrumented sites and structures.

Vertical ground-motion prediction equation and the vertical-to-horizontal spectral ratio for crustal earthquakes in Taiwan

We develop a ground motion prediction equation (GMPE) for estimating the vertical ground motion amplitudes for crustal earthquakes in Taiwan. The data set used for the development includes strong-motion recordings mainly from Taiwan earthquakes (M3.5–7.6) and supplemented with large-magnitude earthquakes (M6.5–7.9) from other regions in the Pacific Earthquake Engineering Research Center (PEER) next generation attenuation (NGA)-West2 database. The functional form of the GMPE is similar to that of Phung et al. developed for the horizontal component (P20). The GMPE provides median and standard deviations of peak ground acceleration (PGA) and 5% damped pseudo spectral acceleration response ordinates of the orientation-independent average horizontal component of ground motion (RotD50) for the spectral period of 0.01–10 s. The vertical ground motion developed in this study can be paired with the P20 horizontal component model to estimate a vertical-to-horizontal (V/H) ratio that is unbiased. In the vertical component, we observe significant nonlinear site effects in the period of about 0.2–0.5 s, moderate nonlinear site effects in the period of about 0.01–0.04 s, and small nonlinear site effects in the period of about 0.05–0.075 s. Compared to our horizontal GMPE, anelastic attenuation is faster, VS30-scaling is reduced, and nonlinear site response is weaker for the vertical component.

Seismic analysis of high-speed railway irregular bridge\u2013track system considering V-shaped canyon effect

To explore the effect of canyon topography on the seismic response of railway irregular bridge–track system that crosses a V-shaped canyon, seismic ground motions of the horizontal site and V-shaped canyon site were simulated through theoretical analysis with 12 earthquake records selected from the Pacific Earthquake Engineering Research Center (PEER) Strong Ground Motion Database matching the site condition of the bridge. Nonlinear seismic response analyses of an existing 11-span irregular simply supported railway bridge–track system were performed under the simulated spatially varying ground motions. The effects of the V-shaped canyon topography on the peak ground acceleration at bridge foundations and seismic responses of the bridge–track system were analyzed. Comparisons between the results of horizontal and V-shaped canyon sites show that the top relative displacement between adjacent piers at the junction of the incident side and the back side of the V-shaped site is almost two times that of the horizontal site, which also determines the seismic response of the fastener. The maximum displacement of the fastener occurs in the V-shaped canyon site and is 1.4 times larger than that in the horizontal site. Neglecting the effect of V-shaped canyon leads to the inappropriate assessment of the maximum seismic response of the irregular high-speed railway bridge–track system. Moreover, engineers should focus on the girder end to the left or right of the two fasteners within the distance of track seismic damage.