Multi-support Seismic Excitations Research Articles

A method for linear response analysis of long bridges under multi-support seismic excitation

A method for linear response analysis of long bridges under multi-support seismic excitation

Stochastic dynamic analysis of the train-track-bridge system under tridirectional spatially correlated ground motions

Due to seismic spatial variation and the correlation between tridirectional ground motions, the random vibrations of the train-track-bridge system are different from those under uniform seismic excitations. To study this difference, a high-speed train traversing a multi-span bridge under both track irregularities and tridirectional spatially correlated ground motions is investigated by using the pseudo-excitation method. Through calculating stochastic dynamic responses of the system, the influences of seismic spatial variation and the correlation between tridirectional ground motions are evaluated for the maximum standard deviations of bridge accelerations, train accelerations, the wheel-rail contact force, and the offload factor. The results show that these influences significantly affect the stochastic dynamic responses of the train-track-bridge system. Therefore, they cannot be ignored in the stochastic dynamic analysis of the train-track-bridge system under multi-support seismic excitations.

Exploring a generalized nonlinear multi-span bridge system subject to multi-support excitation using a Bouc-Wen hysteretic model

This paper presents a generalized reduced-order nonlinear model subjected to multi-support seismic excitation. The hysteretic, nonlinear, relationship of piers is phenomenologically captured by a calibrated Bouc-Wen model. This generalized reduced-order model is benchmarked against legacy physical experimental tests performed at the University of Bristol.A deterministic approach using real spatiotemporal ground motions recorded at the SMART-1 array, Taiwan, is employed as an alternative to a stochastic methodology used in current provision codes. This is so that the influence of nonlinearity and ground motion aleatory and epistemic effects are fully captured. Incremental Dynamic Analysis (IDA) is then performed to identify the performance levels at which this system transitions from elastic to inelastic behaviour. A parametric study is then performed to explore the effect of the spatial variability of the ground motion while bridge alignment, valley profile and ground motion intensity are modified. Results indicate that bridges over shallow valleys with a central rise are prone to significant analysis errors if multi-support excitation is not employed.

A theoretical and experimental exploration of the seismic dynamics of multi-span bridges

A generalized reduced-order model of a multi-span continuous bridge, on flexible discrete supports, that is subjected to multi-support seismic excitation is presented. This model highlights the key non-dimensional system parameters. Real spatiotemporal ground motion time-series (from the SMART-1 array, Taiwan) are used, as an alternative to employing artificial ground motion based on some spatial incoherence kernels. Benchmark experimental test data, using the multiple support excitation rig of a four-span bridge and SMART-1 array excitation, is used to validate/calibrate the proposed reduced-order model. An operational modal analysis is conducted to obtain least-square estimates of these key dynamic parameters using a Levenberg–Marquardt algorithm. The computationally efficient reduced-order model is then employed for a parametric study that explores the effect of spatial incoherence, bridge alignment and archetypal symmetrical and asymmetrical bridge geometries. A comparison of identical and multi-support excitation cases indicate the likely range of beneficial/adverse errors in neglecting the spatiotemporal nature of ground motions in design analyses.

Influence of Actual Site Soil Layers on Pounding of a High-Pier Bridge Occurred between Deck and Abutment

This study aims to determine the pounding probability of a continuous rigid bridge with high piers and long span at the actual site soil under the action of an earthquake. Finite element models of the bridge are built to analyze separation length. The effect of the actual site soil on seismic wave propagation from the bedrock to the pier and the abutment foundation is considered using DEEPSOIL software. A pounding probability analysis method under multi-support seismic excitations with bedrock peak acceleration as the strength index is proposed. The pounding probability of the continuous rigid bridge with high piers and long span under multi-support seismic excitations is analyzed using the proposed method. Meanwhile, a comparison analysis of the pounding probability results under uniform excitations without considering the influence of the actual site soil is performed. The study indicates that the required width of the expansion joint under uniform excitation is larger than the multi-support excitation with the increase in bedrock peak acceleration. With the increase in the width of expansion joint and the acceleration peak, the probability of pounding at a single abutment and at two abutments under multi-support excitation is gradually less than uniform excitation. Therefore, the actual site soil must be considered when determining the width of the expansion joint of a continuous rigid bridge with high piers and long span.

ASSESSMENT OF SEISMIC PERFORMANCE OF SUBMERGED FLOATING TUNNEL UNDER MULTI-SUPPORT SEISMIC EXCITATIONS

Submerged floating tunnel (SFT) is an innovative structural solution for the transportation infrastructure through sea straits, fjords, and inland waters and is an economical alternative to the long-span cable-supported bridge, immersed tunnel, or underground tunnel. An SFT is a massive cylindrical structure that floats at a certain depth below the water surface and subjected to extreme environmental conditions, such as waves, tsunamis and earthquakes. The seismic assessment of SFT supported by mooring cables, under multi-support seismic excitations needs to be evaluated in more detail. The time domain dynamic problem of SFT moored by inclined mooring cables/anchors is formulated and the geometric non-linear dynamic analysis of SFT subjected to hydrodynamic and seismic excitations is performed in this paper. The prototype of SFT to be constructed in Qindao Lake of China is analysed under multi-support seismic excitations. It was found that due to the fluid environment and flexible cables the effective seismic forces are dissipated well and SFT is stable under the spectrum compatible ground motions. However, the lateral component of seismic excitations produce larger responses compared to longitudinal one and may be critical for other case studies.

Simulation of spatially variable seismic underground motions in saturated double-phase media with overlying water excited by SV-wave and difference from P-wave incidence

The spatial seismic excitations affected by water-saturated soil, a double-phase medium, and overlying water are desirable to be considered for evaluating the seismic response of some typical structures such as large-span cross-sea bridges considering soil-structure interaction. This paper focuses on the study of a theoretical method and numerical simulation of multi-support seismic underground excitations in saturated soil with overlying water for obliquely incident SV waves that can produce P1, P2 and SV waves in saturated soil. First, the reflection coefficients (results are different from the case for P waves incidence) of three kinds of waves (P1, P2, SV) at the interface between saturated soil and overlying water are derived. Based on the reflection coefficients and the boundary conditions at the elastic solid-saturated soil interface, the transfer functions of soil layers with arbitrary depths are proposed to calculate the key elements (i.e., the underground power spectral density, response spectrum function and underground coherency function) for generating the multi-support seismic underground motions. Second, these three key elements are used to establish the underground power spectral matrix, and then the underground motions are generated by decomposing the matrix. Finally, the method is verified by numerical examples and the influences of overlying water depth and incident angle on ground motions are investigated. The effect of incident angle on transfer functions show great difference between the small-angle and large-angle case. Moreover, the phenomenon that is diffrent from P-waves incidence case is investigated,found and emphasized, and the reasons are given.

The effect of local topography on the seismic response of a coupled train-bridge system

The local topography has a significant effect on the characteristics of seismic ground motion. This paper investigates the influence of topographic effects on the seismic response of a train-bridge system. A 3-D finite element model with local absorbing boundary conditions is established for the local site. The time histories of seismic ground motion are converted into equivalent loads on the artificial boundary, to obtain the seismic input at the bridge supports. The analysis of the train-bridge system subjected to multi-support seismic excitations is performed, by applying the displacement time histories of the seismic ground motion to the bridge supports. In a case study considering a bridge with a span of 466 m crossing a valley, the seismic response of the train-bridge system is analyzed. The results show that the local topography and the incident angle of seismic waves have a significant effect on the seismic response of the train-bridge system. Leaving these effects out of consideration may lead to unsafe analysis results.

Seismic Response of Double Thin–Wall Continuous Rigid Frame Bridge Considering Traveling Wave Effect

A double thin-wall continuous rigid frame bridge with a span of (68 + 116 + 68)m is selected as the engineering background in this study. A full-bridge finite element model is established with the assistance of MIDAS software to analyze the seismic performance of double thin–wall continuous rigid frame bridge. The multi-support seismic excitation is applied to consider the traveling wave effect. The results show that the self-vibration period of the double-thin continuous rigid frame bridge decreases with the increase of the double-limb spacing. The seismic responses obtained by considering travelling effect tend to those obtained without considering travelling effect when the apparent velocity increases. The seismic responses of the substructure are reduced by considering the traveling wave effect, while the traveling wave effect has significant effect on the superstructure. The axial force of the girder with considering the traveling wave effect is 3 times greater than that with uniform excitation. Therefore, the preliminary design or seismic analysis of the double thin-walled structure should focus on the influence of the traveling wave effect on the superstructure.

Influence of Gap Size on the Dynamic Behavior of Perforated Tube under Seismic Excitation

Perforated tubes form a part of the reactor regulating and protection system in Indian Pressurized Heavy Water Reactors (IPHWRs). These tubes are being analyzed for design basis and beyond design basis seismic loading conditions. Experimental studies have been carried out on full scale shutdown system sub-assembly to evaluate the responses of the perforated tube under multi support seismic excitation. Dynamic characterization of the tube subjected to seismic excitation, simulating rock site and alluvium soil condition, has been carried out. In order to study the interaction of these tubes with the nearby structure/assemblies under beyond design basis seismic excitation, experimental studies have also been carried out to quantify the variation of impact forces with gap sizes, and their influence on the dynamic behavior of these tubes. Non-linear analytical calculations have been carried out simulating the above test conditions. Responses from experimental and analytical studies have been compared, and are found to be in good agreement.

Tail-Equivalent Linearization of Inelastic Multisupport Structures Subjected to Spatially Varying Stochastic Ground Motion

AbstractAfter a brief review of time- and frequency-domain tail-equivalent linearization methods (TELM) for uniform excitation problems, this paper extends TELM for application to nonlinear systems subjected to multisupport seismic excitations. The spatial variability of the ground motion is represented by a coherency function that characterizes the incoherence, wave-passage, and site-response effects. It is found that for multisupport excitation problems, it is most convenient to formulate TELM by using the ground displacement as input. The resulting tail-equivalent linear system (TELS) is defined by frequency-response functions relating the response quantity of interest to each support displacement. A method to reduce the number of random variables in the TELM analysis is introduced. The proposed method is demonstrated through numerical examples with varying structural properties and ground motion coherency in order to investigate various aspects of TELM and the major influences of differential support ...

Completeness Verification of Complex Response Spectrum Method for Underdamped and Overdamped Multiple-Support Systems Regarding the Decoupled Damping as Mathematical Parameter without Physical Meaning

The completeness of the complex response spectrum method for both formally underdamped and overdamped modes is theoretically proved, and the physical meanings of the decoupled modes as well as involved parameters are recognized and clarified in this paper. For the system with relatively large non-classical damping, the eigenvalue pairs generated by the complex mode decomposition method are real and the so-called modal damping ratios are larger than unity. In this paper, we firstly clarified that the decoupled modes are virtual and the so-called modal frequency and damping ratio are mathematical parameters that have no physical meaning. Then, the completeness of the complex response spectrum method for both formally underdamped and overdamped modes is rigorously proved by allowing the “damping frequency” to be an imaginary number. For the virtually overdamped modes, Duhamel integral involved in the calculation for formally underdamped modes automatically convert to hyperbolic Duhamel integral. A numerical example taken from the published literature is given to verify this method. Structural responses for the system with coupled damping under multi-support seismic excitations are further analyzed and numerical results indicate the accuracy of complex response spectrum method.

Seismic analysis of offshore wind turbine including fluid-structure-soil interaction

This paper presents the seismic response analysis of offshore wind turbines subjected to multi-support seismic excitation by using a three dimensional numerical finite element model considering viscous boundaries. The sea water-offshore wind turbine-soil interaction system is modeled by the Lagrangian (displacement-based) fluid and solid-quadrilateral-isoparametric finite elements. The research conducts a parametric study to estimate the effects of different foundation soil types on the seismic behavior of the offshore wind turbine coupled interaction system. The results obtained for different cases are compared with each other.

SEISMIC RESPONSE OF POWER TRANSMISSION TOWER-LINE SYSTEM UNDER MULTI-COMPONENT MULTI-SUPPORT EXCITATIONS

The effect of multi-component multi-support excitations on the response of power transmission tower-line system is analyzed in this paper, using three-dimensional finite element time-stepping analysis of a transmission tower-line system based on an actual project. Multi-component multi-support earthquake input waves are generated based on the Code for Design of Seismic of Electrical Installations. Geometric non-linearity was considered in the analysis. An extensive parametric study was conducted to investigate the behavior of the transmission tower-line system under multi-component multi-support seismic excitations. The parameters include single-component multi-support ground motions, multi-component multi-support ground motions, the correlations among the three-component of multi-component multi-support ground motions, the spatial correlation of multi-component multi-support ground motions, the incident angle of multi-component multi-support seismic waves, the ratio of the peak values of the three-component of multi-component multi-support ground motions, and site condition with apparent wave velocity of multi-component multi-support ground motions.

MR Damper Semiactive Control for Bridge under Multi-Support Seismic Excitation

For vibration control of long-span arch bridges under multi-support seismic excitation, this paper presents schemes of control to seismic responses of arch bridges with Magneto-Rheological dampers(MRD). In the semi-active control system of arch bridge-MRD, Linear Quadratic Gaussian (LQG)-based Sign function control algorithm is used to command MRD，and traveling wave effects on the responses of structure are considered. The Nimu arch bridge is used as a simulation example to verify the proposed control scheme. Numerical results show that traveling wave effects have no unfavorable influence on the control to response of arch bridge.

Influence of Traveling Wave Effect on Passive Seismic Control of Long-Span Bridge

The vibration control to responses of long-span bridges induced by seismic excitation is an important way to improve the safety of the structure. This paper deals with the analysis of the seismic behavior of bridge equipped with viscous dampers when subjected to multi-support seismic excitation, focusing on the traveling wave effect on seismic response. A scheme of passive control to long-span top-through arch bridges, on which the viscous dampers are arranged, is presented. A calculation method of passive control to bridge is derived considering multi-support seismic excitation, and nonlinear dynamic analysis by means of state variable equation integration is employed to examine the seismic behavior of arch bridge with the supplemental nonlinear viscous dampers. In order to study the influence of traveling wave effect on the seismic control of bridge, taking Nimu arch bridge in Tibet as an example, this paper analyzes the seismic response of bridge under multi-support seismic excitation with wave-velocity changing. Numerical results show that traveling wave effects have a major influence on the vibration-suppressed efficiency of passive control for the bridge. Generally, the effectiveness of control to displacement and internal force become better with wave-velocity increasing. As for internal force, the control of moment is superior to that of thrust.

Dynamic analysis of a train-bridge system under multi-support seismic excitations

A numerical solution for the dynamic responses of a train-bridge interaction system subjected to multi-support seismic loads was studied. The train vehicle was modeled by the rigid-body dynamics method, and the bridge was modeled by the finite element method. The vertical and lateral wheel-rail interaction forces were defined according to the wheel-rail corresponding assumption and the simplified Kalker creep theory. Three-dimensional seismic accelerations were incorporated using the large mass method. In a case study, the dynamic responses were simulated for a high-speed train traversing a steel truss cable-stayed bridge with different seismic intensities and different train speeds, and train safety was evaluated.

Seismic response analysis of continuous rigid frame bridge considering canyon topography effects under incident SV waves

To evaluate the importance of the canyon topography effects on large structures, based on a rigid frame bridge across a 137-m-deep and 600-m-wide canyon, the seismic response of the canyon site is analyzed using a two-dimensional finite element model under different seismic SV waves with the assumptions of vertical incidence and oblique incidence to obtain the ground motions, which are used as the excitation input on the pier foundations of the bridge with improved large mass method. The results indicate that canyon topography has significant influences on the ground motions in terms of incident angle. The peak ground acceleration values vary greatly from the bottom of the canyon to the upper corners. Under vertical incident SV waves, at the upper corners of canyon the peak ground accelerations greatly increase; whereas the peak ground accelerations diminish at the bottom corners of canyon. Under oblique incident SV waves, the shaking of the canyon slope perpendicular to the incidence direction is much more severe than that of the opposite side of canyon. And the ground surface has been characterized by larger deformations in the case of oblique incident waves. It is also concluded that the low piers and frame of the continuous rigid frame bridge are more sensitive to the multi-support seismic excitations than the flexible high piers. The canyon topography as well as the oblique incidence of the waves brings the continuous rigid frame bridge severe responses, which should be taken into account in bridge design.

Control mode selection for modal control of long-span arch bridge

For seismic control of arch bridge, a model reduction of long-span arch bridge was implemented based on modal analysis. As for the critical mode selection, an approach based on the maximum modal displacement was presented. This approach takes into consideration the effect of external seismic excitation and is more reasonable than only considering dynamic bridge characteristics based on a modal contribution ratio. The time domain and frequency domain analysis method were used to verify the simplified model of the Nimu arch bridge in Tibet as an example. The numerical results show that the method of maximal modal displacement better analyze long-span arch bridge when multisupport seismic excitation must be considered. The reduced-order system also is more in line with the performance of the original model.

The effects of ice cover on stochastic response of concrete gravity dams to multi-support seismic excitation

article i nfo Article history: Received 4 June 2008 Accepted 17 August 2008 In this study,the ice covereffects on stochasticseismicresponse of concrete gravity dams subjected tomulti- support seismic excitation are investigated including ice-dam-reservoir-foundation interaction. Ice-dam- reservoir-foundation interaction system is modeled by finite element method using ANSYS program. The ice-dam-reservoir interaction system is modeled using the Lagrangian (displacement-based) fluid and solid-quadrilateral-isoparametric finite elements. The ground motion is described by filtered white noise and applied to each support point of the two-dimensional finite element model of the dam reservoir- foundation system. The east-west component of Erzincan earthquake, which occurred on 13 March 1992, is taken into account for the stochastic dynamic analysis of Sariyar concrete gravity dam. Solutions are obtained for dam-reservoir-foundation and ice-dam-reservoir-foundation systems, separately. Parametric studies are conducted in order to investigate effects of the variation of the length, thickness, elasticity modulus and its density of the ice cover on the seismic dynamic response of the dam. It is observed that the variations of the values of the length, thickness, and elasticity modulus (except density) of the ice cover influences the stresses of the coupled system considerably.