Horizontal Earthquake Research Articles

Seismic behavior of lightweight steel frame with thin-walled steel skeleton-lightweight concrete wall

In this study, an innovative prefabricated lightweight steel frame with thin-walled steel skeleton-lightweight concrete composite wall structure (LSF-TSLC) is proposed. The proposed LSF-TSLC has the lightweight steel frame (LSF) as the vertical load-bearing system, whereas the thin-walled steel skeleton-lightweight concrete composite wall (TSLC) acts as the main component for horizontal earthquake resistance. A full-scale LSF specimen and three full-scale LSF-TSLC specimens were prepared considering the variables of wall installation method (embedded, external) and thin-walled steel skeleton distribution (frame type, truss type). The corresponding seismic behavior was experimentally investigated by evaluating the hysteretic characteristics, failure mode, ultimate bearing capacity, deformation performance, stiffness degradation, energy dissipation, and strain characteristics. The results showed that the plastic hinges appeared at the beam ends and column bases of LSF. Due to the shear failure, the embedded and external TSLC exhibited grid cracks and diagonal cracks, respectively. The LSF and TSLC had a good coordinating deformation capacity, while the LSF-TSLC structure had two seismic fortification lines. Compared with LSF, the ultimate bearing capacity and stiffness of LSF-TSLC were increased by 2.1 times and 5.1 times, respectively. The deformation capacity and energy dissipation of LSF-TSLC were significantly improved compared to LSF. The self-tapping nail joint of the embedded wall and the high-strength bolt joint of the external wall had reliable connectivity performance. The numerical simulation of LSF were conducted to verify the plastic analysis model for LSF. And the ultimate bearing capacity calculation method for the LSF-TSLC structure was proposed based on the Strut-and-Tie model.

Study on the damage cause of tunnel junction under different component earthquakes based on on-site investigation and numerical simulation

The Shengli tunnel sustained significant damage during the 2022 Luding earthquake (Mw 6.6), with numerous circumferential and inclined cracks observed in the tunnel lining. This paper develops a three-dimensional numerical model to examine the tunnel junction's dynamic responses to three seismic components: east-west (EW), north-south (NS), and up-down (UD). It also analyzes the causes of tunnel damage. A comparison between the numerical simulation results and the on-site investigation findings shows a high degree of agreement, with damages predominantly concentrated at the junction between the right tunnel and the branch tunnel. The tunnel cross sections' plastic damage areas, damage parameters, K values, and convergent deformation are significantly larger during horizontal vibrations (EW and NS components) than during vertical vibrations (UD component). The stiffness differential between the right and branch tunnels results in varying dynamic responses, leading to geometric incompatibility at the junction as the primary cause of damage. Under horizontal earthquakes, tunnels aligned perpendicular to the vibration direction exhibit significant lateral deformations. Consequently, the extent of damage development in the right tunnel is greater than in the branch tunnel under an EW component earthquake, and the extent of damage development in the branch tunnel is greater than that in the right tunnel under an NS component earthquake. In contrast, damage under the UD component is confined near the junction, without extending into the right or branch tunnels. From an energy perspective, the tunnel system accumulates the least inelastic strain energy during UD component earthquakes, resulting in minimal damage despite the highest Peak Ground Acceleration in the UD direction.

A Classification Method of Earthquake Ground Motion Records Based on the Results of K-Means Clustering Analysis

This paper presents a classification method for earthquake ground motion records utilizing the results of K-means cluster analysis. The moment magnitude and Joyner–Boore distance are utilized as the primary parameters for clustering the earthquake ground motion records. The classification boundaries are established through an examination of moment magnitude ranges, Joyner–Boore distance ranges, and spectral characteristics within each cluster. In this study, a comprehensive dataset comprising 7627 horizontal earthquake acceleration records was meticulously curated for analysis. The data were subjected to separate clustering and grouping procedures, allowing for insightful comparisons between the resultant clusters. Significant disparities in spectral characteristics across the classification groups were demonstrated. These differences become particularly pronounced when a moment magnitude threshold of 6 and a Joyner–Boore distance threshold of 140 km are employed to categorize the ground motion records. The approach underscores the substantial impact of classification based on earthquake ground motion spectral characteristics, while also mitigating the potential instabilities inherent in cluster analysis results. A refined and quantitatively robust framework for understanding and categorizing earthquake ground motions is provided, offering valuable insights for seismic data analysis and contributing to more accurate and reliable assessments of seismic activity.

Directionality characteristics of horizontal response spectra from the 2022 Mw 6.9 Chihshang, Taiwan earthquake

Horizontal earthquake ground motion intensity, and specifically response spectral ordinates, vary with orientation. This phenomenon is usually referred to as ground motion directionality and can be separated into two aspects: the orientation where the maximum spectral response occurs and the variation of response spectral ordinates as the orientation moves away from the orientation of maximum spectral response. This work studies both aspects using the recent 2022 Mw 6.9 Chihshang, Taiwan earthquake, which was recorded by a dense network of strong motion stations with various geological and topographical settings. The mean variation of response spectral ordinates with orientation is found to be slightly more significant than that of previous shallow crustal earthquakes in active tectonic regimes. Moreover, the orientation of maximum spectral response is found to be close to the transverse orientation, which is perpendicular to the orientation at a given site that points to the earthquake epicenter, confirming prior observations made for strike-slip earthquakes. These results suggest that the location of a site relative to the seismic source could be used to modify the outputs of ground motion models to estimate spectral responses at specific horizontal orientations.

Analytical solution for simplifying the pile-soil interaction to a spring-damping system under horizontal vibration

An analytical solution is developed to investigate the model of simplifying the pile-soil interaction to a spring-damping system when the horizontal earthquake input or the top of the model is subjected to horizontal dynamic load. Based on Euler-Bernoulli theory, the dynamic equilibrium equations of pile in soil and air are established, respectively. Then, utilizing the corresponding boundary conditions, potential function decomposition, and transfer matrix method, the analytical expression of impedance at the pile head whether the horizontal earthquake input or the top of the system is subjected to horizontal dynamic load can be presented. Furthermore, the model of the pile-soil complex interaction can be simplified as a spring-damping system according to the stress equilibrium at the pile bottom in the air. Moreover, the rationality of the present solution (without simplification) is verified by comparison with existing methods, and then the difference between the present solution (without simplification) and the spring-damping system (simplification) is also compared. Finally, the influence of the parameter variation in the pile buried in the soil and soil free-field on the simplified model are discussed. The research results will be instructive for the simplification of numerical model for pile-soil interaction.

Mitigating train-induced building vibrations with rubber bearings designed for horizontal earthquake isolation

As rail transportation, including high-speed railways and urban metros, rapidly expands, its proximity to residential areas decreases, raising concerns about ground-borne vibrations. This study investigates the main characteristics of ground-borne vibrations induced by high-speed railways and metros through substructure method based on 2.5D FEM-MFS (finite element method-the method of fundamental solutions). Besides, the study also delves into the vertical vibration behaviors of buildings caused by train operations, evaluating the effect of laminated rubber bearings designed for horizontal seismic isolation on the train-induced building vibration mitigation. Our findings highlight that the broadband vibrations from train operations might coincide with the natural vibration frequencies of buildings, potentially leading to resonance. Implementing isolators allows the natural frequencies of the vibration modes with larger effective masses to be significantly lower than the dominant frequencies of train-induced ground-borne vibration, reducing the high-frequency responses. Additionally, the vibration mitigation enhances with the increase in the thickness of rubber layer. This research not only aims to reduce vibration levels in buildings adjacent to railways, enhancing the living conditions and health of residents but also underscores the engineering innovations necessary for sustainable urban development.

Horizontal ground-motion model for subduction slab earthquakes using offshore ground motions in the Japan Trench area

The S-net, a large-scale network of permanent ocean-bottom seismographs in the Japan Trench, consisting of 150 stations, has recorded a large number of offshore ground motions that can be used to establish the empirical attenuation relationship of offshore ground motions in the subduction zone. Due to the different attenuation characteristics among different earthquake types in subduction zones, the earthquakes are classified into four tectonic types of subduction slab, interface, shallow crustal, and upper-mantle earthquakes according to the classification scheme of Zhao et al. (2015). Predictive models and uncertainties in offshore ground motions were investigated for different earthquake types. This study establishes a horizontal offshore subduction slab earthquake ground-motion model (GMM) and compares the offshore and onshore slab earthquake GMMs. As the site conditions at ocean-bottom stations are different from those at land stations, the effects of water depth and sediment thickness are taken into account in the offshore slab earthquake GMM. Due to differences in the burial methods of ocean-bottom stations, stations were divided into buried and unburied to investigate the effects of the burial methods. Therefore, regression analysis was used to propose an offshore slab earthquake GMM considering the magnitude, focal depth, distance, water depth, sediment thickness, and burial method. By separating the within-event residuals, the single-station standard deviation is presented. Compared to the onshore GMM, the predicted spectra of the offshore GMM are significantly larger at long periods. For the attenuation rate, the offshore attenuation rate is lower than that of the onshore attenuation rate for short periods, but is basically consistent with the onshore attenuation rate for long periods. The proposed GMM can be used to predict the offshore ground motions for slab earthquakes with rupture distances less than 300 km, focal depths less than 110 km, and moment magnitude between 4 and 7.4.

Seismic Response Analysis of Multi Span Hyperbolic Brick Arch Thin Shell Structure

The research objective is to investigate the multi-span hyperbolic brick arch thin-shell structure located in Changleyuan, Baoji City, Shaanxi Province. The study utilizes on-site dynamic testing and finite element numerical simulation methods to analyze the dynamic characteristics of the thin-shell structure and its seismic response under various seismic waves and directions. The simulation results indicate the following findings: Vertical earthquakes cause more severe damage to structures compared to horizontal earthquakes. Bidirectional seismic excitation has a greater impact on the structure than unidirectional and three-dimensional seismic excitation. The obtained results provide a scientific basis for the seismic protection, reinforcement, and repair of this multi-span double-curved brick arch thin-shell structure.

Effects of Higher Sloshing Modes on the Response of Rectangular Concrete Water Storage Tanks with Different Aspect Ratios to Near-Field Earthquakes

Near-field earthquakes have been shown to have different effects on structures than far-field events. This study examines the dynamic response of a rectangular concrete liquid storage tank with tapered walls to near-field ground motions, with particular emphasis on the effect of higher sloshing modes. The tank’s numerical modeling, calibrated using experimental results, was performed considering the tank’s wall flexibility. Seven selected near-field records were applied in each case, and the effects of the first five sloshing modes on the tank response at three different locations, including the corner, middle of the long wall, and middle of the short wall, were investigated. The effect of the earthquake incident angle on the tank’s response was also studied by applying major and minor horizontal earthquake components once along the longer and shorter tank walls, respectively, and vice versa. Results show that the tank corner may have a sloshing height up to 50% greater than the middle of the walls and that the maximum sloshing response is substantially influenced by the spectral acceleration value at the first sloshing period. Higher sloshing modes are found to affect the sloshing response, with a maximum R2 score of 0.95, depending on the excitation’s incidence angle.

Evaluation of the effect of the vertical component of an earthquake on the seismic response of container cranes using the shake table test

In this study, the effect of the vertical component of earthquakes on the seismic response of a container crane was investigated by using the shake table test on a 1/20 scale container crane. The effect was investigated by comparing the seismic response of the container crane when subjected to the horizontal component of earthquakes versus the horizontal and vertical components of earthquakes. The seismic responses of the container crane were compared based on acceleration responses, displacements, and internal forces. The main findings of this study are as follows: (1) Vertical acceleration response increased when the vertical and horizontal components of earthquakes were used simultaneously. A maximum increase of 79% was observed for the vertical acceleration response at the trolley-boom girder. The horizontal acceleration response either increased or decreased. The maximum difference was 24% when the container crane was subjected to horizontal component earthquakes versus horizontal and vertical component earthquakes. (2) The horizontal displacements of the container crane increased or decreased under the simultaneous action of the horizontal and vertical components of the earthquakes. The maximum difference was 278% with regard to the derailment of the seaside legs. (3) The internal forces at the top of the lower legs were affected by adding the vertical component of the earthquakes. The maximum difference in the axial force response was 100%, while that of the bending moment was 24%. Therefore, the seismic response of container cranes should be analyzed with and without the vertical component of earthquakes to determine the most extreme case of the seismic response.

Shaking table test and numerical simulation of a precast frame-shear wall structure with innovative untopped precast concrete floors

An innovative discretely connected precast concrete floor (DCPCF) was presented, in which the adjacent precast concrete hollow or sandwich flat slabs were connected by mechanical connectors embedded in the precast concrete slabs and beams. This paper summarized the seismic performance observed during the shaking table test of a precast frame-shear wall structure adopting DCPCF. A 1/4-scale model of a 4-storey 2-bay single-span frame-shear wall structure was designed and tested on the shaking table to evaluate the dynamic characteristics and seismic responses of building structures adopting DCPCF. In addition, a finite element model, including detailed modeling of beam-column joint and slab joint connections, was established using nonlinear dynamic modeling program. The predictions on the seismic performance using the finite element model agreed well with the test results for the designed frame-shear wall structure. The precast concrete frame-shear wall structure adopting DCPCF had satisfactory seismic performance during the test process. The in-plane deformation of DCPCF was observed under the horizontal earthquakes, and DCPCF could not satisfy the requirements of rigid diaphragm assumption in most cases under design basis seismic intensity. The seismic design method based on semi-rigid floor diaphragm had large error and safety risk in calculating the seismic shear force of building structure adopting DCPCF. Additionally, design suggestions for multi-storey and high-rise building structures using DCPCF were proposed based on the observed seismic responses.

Comment on “Effect of Style of Faulting on the Orientation of Maximum Horizontal Earthquake Response Spectra” by Alan Poulos and Eduardo Miranda

Comment on “Effect of Style of Faulting on the Orientation of Maximum Horizontal Earthquake Response Spectra” by Alan Poulos and Eduardo Miranda

Reply to “Comment on ‘Effect of Style of Faulting on the Orientation of Maximum Horizontal Earthquake Response Spectra’ by Alan Poulos and Eduardo Miranda” by Paul Somerville

Reply to “Comment on ‘Effect of Style of Faulting on the Orientation of Maximum Horizontal Earthquake Response Spectra’ by Alan Poulos and Eduardo Miranda” by Paul Somerville

Seismic responses and vibration control of offshore wind turbines considering hydrodynamic effects based on underwater shaking table tests

AbstractThe recent construction of numerous offshore wind turbines (OWTs) in seismically active areas worldwide has stimulated research on seismic evaluation and vibration control design for OWTs. Unlike the onshore counterparts, the hydrodynamic effects on the seismic responses of OWTs need to be studied. Besides, the equipment in the nacelle of an OWT is highly sensitive to acceleration. Significant dynamic amplification on the nacelle under horizontal earthquake excitation can cause the malfunction of power generation and even seriously threaten the safety of OWTs. As a promising solution, tuned mass dampers (TMDs) based on the first mode of OWTs need to be tested by various earthquake excitations. In this paper, the seismic amplification effect, the hydrodynamic effects, and the vibration control by a single TMD are investigated through a series of underwater shaking table tests based on a 1:20 scaled model of a 5 MW OWT. The “no water”, “with water”, and “with water and TMD” tests are evaluated and compared. The accelerations of OWTs can be amplified or reduced by the hydrodynamic effects, depending on the natural frequencies and vibration modes of the OWT and the frequency spectrum of the seismic excitation. The earthquake‐induced hydrodynamic damping ratio and hydrodynamic added mass are carefully measured. For the TMD's effect, the single TMD performs reasonably well in seismic vibration control in most cases. Finally, the interaction between hydrodynamic effects and TMD's effect is discussed, and the hydrodynamic damping effect is suggested to be ignored when designing TMDs for OWTs.

A three-dimensional numerical simulation method for seismic nonlinear response of underground structure in liquefiable site and analysis of structural damage

Considering the effect of dynamic interaction between liquefiable soil and underground structure, simulating the nonlinear seismic response of underground structures through simple, convenient, and reliable 3D numerical model is still a great challenge at present. A three-dimensional numerical simulation method for dynamic response of underground structure in liquefiable site is proposed based on the centrifuge shaking table test designed for a subway station buried in liquefiable interlayer site carried out in the previous period. The numerical model takes into account the characteristics of sand prone to large deformation after liquefaction and the nonlinear characteristics of the contact between saturated soil and structure. The typical numerical calculation results are compared with the experimental results to verify the correctness of the numerical model, and the extended analysis of the structural damage is carried out, which visually shows the damage distribution of structure under different functional states after earthquake. The analysis of structural damage shows that the junction position of middle column and longitudinal beam is more prone to tensile damage under the horizontal earthquake action; while after considering the horizontal-vertical seismic effect, the middle column will produce additional compressive damage due to the vertical inertia force, and the end of middle column should be paid attention to in seismic design.

Seismic response of subway station subjected to mainshock-aftershock sequences by centrifuge shaking table tests

During the 1995 Kobe earthquake, the Daikai Station suffered a severe collapse, drawing more attention to the earthquake damage response of underground structures. However, the performance of underground structures under the mainshock-aftershock sequences has yet to receive much attention. In this paper, the dynamic response and damage development process of the subway station under the mainshock-aftershock sequence were studied and explored through a series of centrifuge shaking table tests. The Selection-Adjustment-Generation method of artificial main aftershock sequence construction was introduced. Steel grits were mixed into the overlying soil to simulate the vertical inertia force. It is found that the Selection-Adjustment-Generation method is easily implemented, maintaining the local time-frequency characteristics of the original seismic waves as much as possible. The failure mechanism of the subway station subjected to mainshock-aftershock sequences can be summarized into two main aspects. One is the reduction of the horizontal deformation capacity of the columns due to the vertical inertial force induced by the overlying soil under the vertical seismic load. Sudden brittle failure will happen to the columns with higher axial pressure under horizontal earthquakes, which weakens their vertical support capacity. The other is the damage accumulation under mainshock-aftershock sequences. The station in the dry sand site is more susceptible to damage for the amplification effect. Both ends of the columns of the subway station experience crack with a strain exceeding 500 με during the mainshock. During the second aftershock, the bottom of the outer columns was crushed. In the liquefiable site, the liquefied layer weakens the upward propagation of horizontal seismic load and protects the structure to a certain extent. This series of tests illustrate the damage development process of underground structures under the main-aftershock and provides valuable experimental data for further study of the earthquake damage response of underground structures.

Transverse seismic responses of a shield tunnel considering the influence of segment joints

The segment joints of a shield tunnel are generally the weak components of the structure, and they can be considerably damaged under strong seismic loading, thus influencing the overall seismic behavior. In this study, Finite Element simulation analyses of centrifuge shaking table tests and a shield tunnel project are carried out to investigate the influences of the segment joints on the seismic responses and the associated mechanisms. First, the reliability of the numerical procedure is validated by using the centrifuge shaking table test results. The numerical procedure is then used, together with the refined simulation approach for segment joints, to carry out extensive numerical analyses of the seismic responses of a shield tunnel project under different horizontal earthquake loadings. The research results show that due to the influence of the segment joints, the peak value of the dynamic bending moment of each segment tends to be more uniform. When the stiffness reduction method is used to consider the influence of the segment joints, the peak values of the dynamic bending moments can be too large, while the peak values of the dynamic axial forces may be too small. In addition, the tunnel segment rotates during an earthquake, resulting in relatively large relative displacements of the segment joints.

Numerical investigation of a proposed multidimensional isolator applied to large-scale domes subjected to earthquakes

A three-dimensional seismic isolation device that is effective in isolating both horizontal and vertical earthquake components has drawn the interest of researchers in recent years. This paper proposes a new three-dimensional isolator for large-scale dome structures, which is composed of a quintuple friction pendulum component and a stacked disc spring component in series in the vertical direction. The complex working characteristics of these components are investigated in detail. Numerical modeling methods are proposed to simulate this isolator for engineering application purposes, and the model accuracy is validated based on theory and experiments. Thus, the isolator is applied to a large-scale dome structure subjected to near- and far-fault ground motions. Numerical analysis shows that the proposed modeling methods can efficiently analyze the isolation performance of the isolator in a large-scale structure. The numerical results demonstrate that the isolator has excellent isolation performance not only for displacement and axial force demands but also for velocity and acceleration demands in all three directions. In addition, according to the comparative study of this paper, the isolation performance of the proposed isolator is better than that of other types of isolators under major earthquakes due to the adaptive sliding characteristics of the quintuple friction pendulum component and the flexibility of the stacked disc spring component prolonging the structural periods.

Experimental and analytical investigations on horizontal behavior of full-scale thick rubber bearings

Thick rubber bearings (TRBs) have been proven to be effective in mitigating both horizontal earthquakes and railway-induced vertical vibration. Due to their low first shape factor, the horizontal properties of TRBs should be carefully examined during isolation design. This study presents experimental and analytical investigations on the horizontal behavior of TRBs with different first and second shape factors (S1 and S2). Eight full-scale thick natural rubber bearings (TNRBs) and lead thick rubber bearings (LTRBs) specimens were designed and tested under shear loading. The effects of geometric parameters and loading conditions were explored. The test results showed that decreasing S1 slightly reduced the horizontal stiffness, whereas the reduction caused by the decrease of S2 was more pronounced. As the applied vertical pressure increased, the horizontal stiffness of both TNRBs and LTRBs reduced, while the yield strength and damping ratio of LTRBs increased. Besides, equations were developed to predict the variations in shear properties of TNRBs and LTRBs under varying shear strains. Then, the test results were used to assess the accuracy of existing formulations for the shear properties of rubber bearings. Accurate equations were determined for the effective stiffness of TNRBs, as well as the yield strength and post-yield stiffness of LTRBs. Moreover, this study validated accurate hysteretic models to predict the cyclic shear behavior of TNRBs and LTRBs.

Seismic design and performance analysis of perforated rubber buffer layer in tunnel

Tunnels may be damaged under earthquakes, which has been observed by many earthquake events, and the buffer layer is proposed and widely investigated as a damping measure. The rubber is considered as a qualified buffer layer material because of its small elastic modulus and super elasticity, but its high price makes it difficult to apply in practical engineering. Therefore, four types of rubber buffer layers are proposed in this study, including the common rubber buffer layer and three types of perforated rubber buffer layers (PRBL), which can reduce the seismic damage and cost of tunnels. A pseudo-static method for calculating the seismic response of tunnels under horizontal and vertical earthquake motions is proposed and verified. Based on proposed pseudo-static method, a seismic design method for the buffer layer is present, and the proposed seismic design process is used to study the seismic mitigation performance of buffer layers. The initial design of the buffer layer under earthquake action E1 is carried out by pseudo-static method, and then the seismic mitigation performance is verified through dynamic time history analysis method under earthquake action E2. The earthquake action E1 and earthquake action E2 are the earthquake actions with short and long return periods of the engineering site, respectively. The results show that the common rubber buffer layer has almost no seismic mitigation performance, and the three types of PRBLs have good seismic mitigation performance. The type IV buffer layer is strip-shaped PRBL and the holes are along the longitudinal direction of the tunnel, and it has optimal seismic mitigation performance. The effects of vertical earthquake motion and peak ground acceleration (PGA) on the seismic mitigation performance of the buffer layer are studied. The results show that vertical earthquake motion has little effect on the seismic mitigation performance of different types of buffer layers. For different PGAs, the type IV buffer layer is able to efficiently decrease the peak internal force of secondary lining. The results also prove the validity of design method.