Vertical Earthquake Excitation Research Articles

The effect of high-speed railway train on the seismic response of bridge under earthquakes

This study aims to discuss the effect of high-speed railway train on the seismic response of bridge girder under earthquakes especially pay attention to the possible response reduction to the bridge caused by vehicle, utilizing experimental and simulation methods. A 1:10 scale model for the train-track-bridge system was built and a high-speed train running test platform based on shaking table array was constructed for the seismic loading test at varying running speed. To account the effects of different earthquake characteristics, earthquakes under the four types of site soil in the far-field and near-field were selected. The vehicle was modeled in two kinds of ways to distinguish the effects of spring-mass vehicle and additional mass which means a vehicle was set with spring suspension and mass, while another with additional mass only. Through a large amount of numerical simulation dates to determine the distribution interval of specific reduction value caused by the vehicle under the earthquake. Results in running tests and numerical simulation indicate that the lateral acceleration of the bridge girder can be effectively reduced when the train is stationary. The reduced ratios were about 4%− 8% compared without train on bridges. As the speed increases, the response of bridge is generally intense and the reduction is also weakened. Similar reduction was not observed in the response of vertical earthquake excitations, and high-frequency earthquakes have adversely affected this kind of reduction. The main reason for the reduction of lateral seismic response of bridge girder in the presence of static vehicle can be attributed to the phase difference between vehicle and bridge caused by a mass damper-like action, and the additional mass cannot cause similar changes alone.

Vehicle-bridge interaction and the tuned-mass damper effect on bridges during vertical earthquake excitation

Vehicle-bridge interaction and the tuned-mass damper effect on bridges during vertical earthquake excitation

Modeling and analysis of cable vibrations in cable-stayed bridges under near-fault ground motions

To represent the cable vibrations of cable-stayed bridges under earthquake actions, this study proposes to model each cable using the multiple nonlinear truss elements with an initial strain and an equivalent number of elastic beam-column elements with a zero cross-sectional area in parallel. The novel method facilitates the bridge model to reach the equilibrium state under the dead loads and enables to take into account the cable nonlinear vibrations as well as cable loosening under seismic events. Then the seismic responses of a case cable-stayed bridge are investigated under near-fault ground motions. It reveals that both the external vibrations and parametric vibrations might develop in the stay cables, depending on the cable locations and earthquake input directions. The traditional method, using one truss element to represent the cable, would for most cases overestimate the seismic responses of the cable, the tower and the deck. Especially, the overestimation is significant under the longitudinal and vertical earthquake excitations as the stiffening effect significantly reduces the nonlinear parametric vibrations of stay cables. The exception is when the bridge is subjected to the transverse seismic inputs only where the external vibrations increase the cable force vibration amplitudes. The present study highlights the importance of modelling the stay cables with multiple elements and including the bi-directional or tri-directional earthquake inputs when conducting seismic analyses of cable-stayed bridges.

Response of soil–pile–superstructure–quay wall system to lateral displacement under horizontal and vertical earthquake excitations

The excess pore water pressure generated under the combined vertical and horizontal earthquake excitations is generally greater than that under the unidirectional excitation, which may further affect the dynamic response of soil-pile-superstructure-quay wall (SPSQ) system. This study conducted a coupled effective-stress analysis for the response of SPSQ system to liquefaction-induced lateral displacement under horizontal and vertical earthquake excitations. To accurately describe the lateral displacement behind the quay wall, the liquefaction behavior of soils was described by a modified generalized plasticity model with parameters properly determined from laboratory tests. The numerical model of the SPSQ system was validated against the previously reported centrifuge model tests. The results show that the earthquake excitation with abundant low-frequency component causes greater residual lateral displacements of pile cap (ux,RC) and quay wall (ux,RQ) than that with abundant high-frequency component. The ux,RC and ux,RQ tend to increase as the peak vertical acceleration increases for both vertical and inclined piles. Increasing the fixity of the quay wall significantly reduces the influence of vertical ground motion on the ux,RC and ux,RQ. The polarity reversal of the vertical ground motion also has a significant effect on the ux,RC and ux,RQ and should be considered in the analyses. In addition, the lateral displacement of liquefied ground causes an amount of rotation of the cap of the inclined pile, probably leading to the potential shear failure at the head of piles. Special consideration should be given to the earthquake-induced shear force at deeper location because the shear force could be significantly greater than that at the head of both inclined and vertical piles in certain cases.

Seismic performance of a wind turbine tower under near-field vertical earthquake excitation

For researching the influence of vertical component of near-field records on the seismic response of wind turbine towers, firstly, shaking table test of a 1/20 scaled 2.0 MW wind turbine is carried out. Second, the finite element (FE) model of the scaled tested model is established by ABAQUS. Finally, the dynamic stability is analysed based on the validated FE model. Moreover, the sensitivity of seismic response to different V/H ratios (peak vertical acceleration to horizontal acceleration) of near-field records is analysed through experimental and numerical studies. The results show that the near-field earthquakes have a greater effect on the acceleration and displacement response. The vertical acceleration, vertical displacement and the axial force of this tower are sensitive to the vertical ground motions and the V/H ratios. The larger contributions of vertical component of near-field ground motions lead to smaller safety factors, which is particularly more unfavourable for the dynamic stability of this tower. The middle and lower section of this tower is the dangerous position for local buckling. The influence of the near-field vertical ground motions and a reasonable value of V/H ratios should be better understood and studied, so as to provide guidance for structural seismic design.

Influence of Bearing on Pier Failure Considering the Separation Condition under Near-Fault Earthquake

To study the influence of the near-fault vertical earthquake, the beam-spring-damper-pier model is used to simulate the double-span continuous beam bridge. The transient wave function expansion method and the indirect mode function method are used to calculate the seismic response of the bridge. The theoretical solutions of the contact force and displacement response of the bridge under vertical earthquake excitation near-fault are derived. By using piers with three different heights, the influence of vertical separation on pier-bending failure is analyzed reasonably. The results show that under the near-fault earthquake action, the split has a certain influence on the pier failure. Moreover, the stiffness and damping of the bearing have an influence on the pier failure, and the change of the maximum pier height has different effects. Therefore, for bridges of different sizes, it is of great significance to select the appropriate stiffness and damping bearings to reduce pier failure.

Experimental investigation on the dynamic response of pile group foundation on liquefiable ground subjected to horizontal and vertical earthquake excitations

Experimental investigation on the dynamic response of pile group foundation on liquefiable ground subjected to horizontal and vertical earthquake excitations

Vibration control of bridges under simultaneous effects of earthquake and moving loads using steel pipe dampers

This study aims to develop a practical methodology based on the eigenfunction expansion method to assess the effects of simultaneous action of vertical earthquake excitation and moving vehicle loads in single-span and multi-span simply-supported bridges. While the effects of vertical earthquake ground motions are generally ignored in common design practice, it is shown that the influence of simultaneous vertical earthquake excitation and vehicle loads can considerably affect the structural response of the bridge, especially in near-field earthquakes with high amplitude vertical components. To address this issue, a novel vibration suppression system is proposed using steel pipe dampers and its reliability is investigated for a wide range of bridge flexural rigidity under seven different earthquake records. The results indicate that the proposed system can significantly (up to 75%) suppress the vertical vibrations generated in the bridge, especially for the systems with lower flexural rigidity. For the same maximum deflection limits, application of pipe dampers could reduce the required flexural rigidity of the bridge (up to 50%), and therefore, lead to more economic design solutions with lower structural weight.

Estimation of Seismic Response of R/C Frame Structures to Vertical Earthquake Motion Considering Fixed Support and Soil-Structure-Interaction (SSI)

The present study aims to demonstrate the effects of vertical earthquake excitation on reinforced concrete frame structures (R/C) incorporating the approaches of Soil-Structure-Interaction (SSI) and rigid foundation. This effect is intended to be determined by making comparative study according to the engineering parameters of the base shear force, base axial force and overturning moment. Three earthquake time-histories currently used for the earthquake analysis of structure in literature are regarded to properly elucidate this effect. For the linear time-history analysis (LMTHA), finite element model (FEM) of a high-rise existing R/C structure designed according Turkish Seismic Code (TSC) is developed through frame, shell, solid, gap, link, linear damper elements. Similar modeling considerations are adopted for infinite soil zone. For the SSI analysis, the Direct Method (DM) is utilized, which enables to make an earthquake analysis of combined FEM (soil model+structure model) instead of separated FEM (the Substructure Method). The comparative study is carried out between the SSI and the fixed support (FS) model with fixed-supports under both only horizontal (H) and horizontal+vertical (HV) seismic motions. The difference between only H and H+V load cases for the engineering parameters that vertical earthquake motion is determined not to be effective on the base shear force, and the SSI model is recommended to be used for analysis due to resulting higher change than the FS. Therefore, no damages/failure resulting from the shear force is estimated under the vertical earthquake motion. Instead, the overturning moment is obtained with great change under H+V for all models; however, the SSI model yields to higher increase than the FS model; so, the SSI model is offered for more reliable analysis. Considerable increase in the overturning moment is predicted that vertical load bearing elements such as, columns and piers need to more strength capacity in terms of bending moment. The highest increase among the other parameters is obtained in the base axial force. However, the percentage increase is resulted as higher under H load than H+V, which means that vertical seismic motion treated as balancing effect. This lower change under H+V load case is directly pertinent to damping properties of the soil media. Therefore, design of columns and piers against axial force is recommended to be made for more safety according to the outcomes from the FS model.

Seismic performance of a resilient low-damage base isolation system under combined vertical and horizontal excitations

Traditional base isolation systems focus on isolating the seismic response of a structure in the horizontal direction. However, in regions where the vertical earthquake excitation is significant (such as near-fault region), a traditional base-isolated building exhibits a significant vertical vibration. To eliminate this shortcoming, a rocking-isolated system named Telescopic Column (TC) is proposed in this paper. Detailed rocking and isolation mechanism of the TC system is presented. The seismic performance of the TC is compared with the traditional elastomeric bearing (EB) and friction pendulum (FP) base-isolated systems. A 4-storey reinforced concrete moment-resisting frame (RC-MRF) is selected as the reference superstructure. The seismic response of the reference superstructure in terms of column axial forces, base shears, floor accelerations, inter-storey drift ratios (IDR) and collapse margin ratios (CMRs) are evaluated using OpenSees. The results of the nonlinear dynamic analysis subjected to multi-directional earthquake excitations show that the superstructure equipped with the newly proposed TC is more resilient and exhibits a superior response with higher margin of safety against collapse when compared with the same superstructure with the traditional base-isolation (BI) system.

Seismic considerations in design of offshore wind turbines

Interest in renewable and clean energy over the past decade has motivated immense research on wind energy. The main issues in design of offshore wind turbines in regions of recent development have been aero- and hydro-dynamic loads; however, earthquake is a design concern in seismic areas such as East Asia and Western United states. This paper reviews the state of practice in seismic design of offshore wind turbines. It is demonstrated that wind turbines are in particular vulnerable to vertical earthquake excitation due to their rather high natural frequencies in vertical direction; however, inclusion of the radiation damping could contribute considerably reduce the earthquake loads. Moreover, it is demonstrated how soil nonlinearity could lead to settlement and permanent tilting of offshore wind turbines on caisson foundations or tripods. Using these cases, the paper demonstrates that the design of offshore wind turbines for earthquake loading is driven by performance-based considerations.

Random Vibration Analysis of Urban Underground Tunnels Under Vertical Earthquake Excitations Based on Mass–Damper–Spring Model

In this paper, the vertical seismic effects on tunnels are studied based on a classic mass–damper–spring model. An analytical discrete model of urban underground tunnels subjected to vertical earthquake excitations is proposed by considering the first vertical vibration mode. Taking a light rail project in Tianjin as an example, this study uses the proposed discrete model to analyze the displacements of tunnel and soil under vertical earthquake excitations. The soil displacement responses at different tunnel locations are analyzed with linear random vibration theory. The computational cost is greatly reduced using the proposed model. It can be seen that different from the case of horizontal earthquakes, the displacement responses under vertical earthquake excitations keep growing after seismic acceleration reaches its peak for a short duration, and then, they begin to decay. The soils at different positions around the tunnels have large relative displacement under vertical earthquake excitations. Moreover, a finite-element model is also established for displacement responses using ABAQUS. The comparison with the results of the finite-element model shows that the results of the proposed discrete model are available.

Dynamic vehicle–bridge interaction under simultaneous vertical earthquake excitation

Traditionally, the seismic response analysis of a bridge does not account for the concurrent vehicle–bridge dynamic interaction. However, the behavior of a seismically excited bridge can jeopardize the safety of the vehicles running on it, even if the bridge itself remains undamaged. This study examines the seismic response of a vehicle–bridge interacting (VBI) system under vertical earthquake excitation, modelling the truck vehicles as rigid body assemblies. An application of the proposed scheme to a realistic case of (highway) bridge—(truck) vehicles shows that the earthquake ground motion and the road surface conditions are the main sources of excitation. The results show that the road surface conditions influence strongly the dynamics of the VBI system, even when the vertical component of the earthquake excitation is significant. Also, the study brings forward the influence of traffic parameters (namely the speed, the number and the distance between the running vehicles) and underlines the need to consider different positions of the vehicle/s (on the deck) during the earthquake shaking. Finally, it examines the tendency of the wheels of a truck vehicle to detach (jump) from the deck during the seismic response of the VBI system. Detachment tends to be more frequent as the road surface conditions deteriorate and/or the peak ground acceleration increases. However, detachment is a complicated phenomenon which depends also on many other ground motion and VBI system parameters and deserves further study.

Vertical earthquake response of megawatt‐sized wind turbine with soil‐structure interaction effects

SummaryThe dynamic response of a wind turbine on monopile is studied under horizontal and vertical earthquake excitations. The analyses are carried out using the finite element program SAP2000. The finite element model of the structure is verified against the results of shake table tests, and the earthquake response of the soil model is verified against analytical solutions of the steady‐state response of homogeneous strata. The focus of the analyses in this paper is the vertical earthquake response of wind turbines including the soil‐structure interaction effects. The analyses are carried out for both a non‐homogeneous stratum and a deep soil using the three‐step method. In addition, a procedure is implemented which allows one to perform coupled soil‐structure interaction analyses by properly tuning the damping in the tower structure. The analyses show amplification of the ground surface acceleration to the top of the tower by a factor of two. These accelerations are capable of causing damage in the turbine and the tower structure, or malfunctioning of the turbine after the earthquake; therefore, vertical earthquake excitation is considered a potential critical loading in design of wind turbines even in low‐to‐moderate seismic areas. Copyright © 2015 John Wiley & Sons, Ltd.

Dynamic Response of a Pendulum Isolator System under Vertical and Horizontal Earthquake Excitation

The paper studies a pendulum isolator. This isolator has a spherical surface which is placed on the foundation and it has an arm which is connected to the column of the building as a hinge. When the height of the arm is less than the curvature radius of the spherical surface, and a small movement is applied on it, a restoring force will be applied to the isolator. In this paper the eect of horizontal and vertical component of seismic load was studied. The dynamic equation of motion was obtained for the pendulum isolator under horizontal and vertical accelerations of seismic loads. The equation was solved by step time integration method. The comparison of the results of horizontal component eect and the combined eect of horizontal and vertical components on the isolator showed that the vertical component eect increased the isolator horizontal displacement response and increased the isolator horizontal acceleration.

Vertical ground motion influence on seismically isolated & unisolated bridges

In this study, influences of vertical ground motion on seismically isolated bridges were investigated for seven different earthquake data. One assessment of bearing effect involves the calculation of vertical earthquake load on the seismically isolated bridges. This paper investigates the influence of vertical earthquake excitation on the response of briefly steel girder composite bridges (SCB) with and without seismic isolation through specifically selected earthquakes. In detail, the bridge is composed of 30m long three spans, concrete double piers at each axis supported by mat foundations with pile systems. At both end of the spans there exists concrete abutments to support superstructure of the bridge. SCBs which were seismically isolated with ten commonly preferred different lead-rubber bearings (LRB) under each steel girder were analyzed. Then, the comparisons were made with a SCB without seismic isolation. Initially, a preliminary design was made and reasonable sections for the bridge have been obtained. As a result of this, the steel girder bridge sections were checked with AASHTO provisions and analytical model was updated accordingly. Earthquake records were thought as the main loading sources. Hence both cases were exposed to tri-axial earthquake loads in order to understand the effects under such circumstances. Seven near fault earthquake data were selected by considering possession of directivity. Several runs using the chosen earthquakes were performed in order to be able to derive satisfactory comparisons between different types of isolators. Analytical calculations were conducted using well known structural analysis software (SAS) SAP2000. Nonlinear time history analysis was performed using the analytical model of the bridge with and without seismic isolation. Response data collected from SAS was used to determine the vertical load on the piers and middle span midspan moment on the steel girders due to the vertical and horizontal component of excitation. Comparisons dealing with the effects of horizontal only and horizontal plus vertical earthquake loads were introduced.

ROCKING AND SLIDING OF ANCIENT TEMPLE COLUMNS UNDER EARTHQUAKE EXCITATIONS

This paper deals with the rocking and sliding behavior of a monolithic stone block or a system of stone blocks under earthquakes, a problem commonly observed for ancient temples in Greece and Southern Italy. The analysis for the above monolithic or multi-drum columns is conducted by a simple process based on generally accepted simplifications. The effects of column geometry, earthquake characteristics and restitution ratio due to impact are also studied herein. Furthermore, an analytical approach for the solution of the complete nonlinear equations of motion (including the one for the vertical earthquake excitation) for the subject considered is proposed. Finally, characteristic representative examples are presented with useful conclusions drawn. It was found that the stability criteria based on static conditions are reliable, while the corresponding dynamic criteria may lead to erroneous results.

Earthquake Response Analysis with Travelling-Wave for a Long-Span Steel Truss-Arch Railway Bridge

In this paper, seismic response properties of a long-span steel truss-arch railway bridge are analyzed in consideration of the travelling-wave effect of multiple earthquake inputs. Vertical earthquake excitations are considered in the study. The internal forces and displacement responses at structurally critical sections under earthquake excitations at multiple supports are evaluated and compared with the emphasis on investigating the travelling-wave effect on the response properties of the bridge. Taft and El-Centro earthquake waves are adopted respectively to account for different earthquake-wave properties. The influence of wave velocity and earthquake property on the structural dynamic responses taking into account travelling-wave effect is discussed.

Seismic Response Analysis of LNG Storage Tank under the Vertical Earthquake Excitation

Use Adina finite element software, established the finite element model of the the volume 10000m3LNG storage tank, against the concrete outer tank of full containment type LNG storage tank vertical seismic action seismic response analysis. Take acceleration seismic input method, select the four categories venue seismic waves, LNG storage tank stress analysis of vertical seismic action, come in different earthquake LNG storage tank outer tank equivalent stress, hoop stress and axial stress distribution.

Fluid-Structure-Soil Interaction Effects on Seismic Behaviour of Elevated Water Tanks

Abstract The multiple base motion effect on hydrodynamic pressure, acceleration of tank and fluid surface elevation problem in Elevated water tank is understood as a Fluid-Structure-Soil Interaction problem. Where, Soil-Structure interaction causes rocking motion and Fluid Structure interaction causes the hydrodynamic behaviour of water tank. According to the available literature, substantial amount of study has been done on behaviour of elevated steel water tank under pure rocking, but no study is done on water tanks with horizontal and vertical earthquake excitation, along with rocking motion. An experimental investigation for a 1:4 scale model of cylindrical steel elevated water tank has been carried out on shake table facility at CSIR-SERC, Chennai. Test program on elevated steel water tank consisted of combined horizontal, vertical and rocking motions, for a synthetic earthquake excitation for 0.1 g and 0.2 g accelerations, with increasing angle of rocking motion. The impulsive base shear and impulsive base moment values increase with increase in earthquake acceleration. Whereas, the convective base shear and base moment values increase for increase in earthquake acceleration, but decrease with increasing angular motion. Hence, there is no considerable effect of rocking motion on sloshing of water. The non-linearity in structure is observed, when the impulsive pressure of tank decreases with increase in tank acceleration. The pressure variation along tank height due to vertical excitation increased with increasing acceleration, and increased furthermore with added rocking. Using various codes available on water tanks, the recorded experimental results were used to calculate and compare the base shear, base moment, pressure variation in the tank.