Multi-support Excitation Research Articles

Improved Large Mass Method for Structural Base Excitation Analysis

To verify the precision and possible applicability of the large mass method (LMM) widely used in multiple-supported structures subjected to non-uniform base excitations, numerical simulations of a two-degrees-of-freedom (2-DOF) finite element model using the Rayleigh damping assumption are performed respectively according to the LMM and the relative motion method (RMM). Through comparisons with the RMM, the error origins and the applicability of the LMM are discussed. Then the improved LMM is presented herein based on the modification of ground motions considering the influences of Rayleigh damping coefficient α. It indicates that the LMM is not applicable to multi-support excitation analysis in the case of Rayleigh damping, which can cause significant errors. And the errors depend on the damping coefficient α. It’s also proved that the improved LMM is able to yield results that are identical to those of the RMM.

Tail-Equivalent Linearization Method in frequency domain and application to marine structures

An extension of the Tail-Equivalent Linearization Method (TELM) to the frequency domain is presented. The extension defines the Tail-Equivalent Linear System in terms of its frequency-response function. This function is obtained by matching the design point of the nonlinear response with that of the linearized response, thus guaranteeing the equivalence of the tail probability of the latter and the first-order approximation of the tail probability of the nonlinear response. The proposed approach is particularly suitable when the input and response processes are stationary, as is usually the case in the analysis of marine structures. When linear waves are considered, the Tail-Equivalent Linear System possesses a number of important properties, such as the capability to account for multi-support excitations and invariance with respect to scaling of the excitation. The latter property significantly enhances the computational efficiency of TELM for analysis with variable sea states. Additionally, the frequency-response function of the Tail-Equivalent Linear System offers insights into the geometry of random vibrations discretized in the frequency domain and into the physical nature of the response process. The proposed approach is applied to the analysis of point-in-time and first-passage statistics of the random sway displacement of a simplified jack-up rig model.

Comparative Study on Multi-Support Excitation Analysis and Actual Recorded Response of Superstructure of Suspension Bridge

Comparative Study on Multi-Support Excitation Analysis and Actual Recorded Response of Superstructure of Suspension Bridge

A Novel Method to Calculate the Dynamic Reliability of Space Structures Subjected to Multi-Dimensional Multi-Support Excitations

Extensively researches have been carried out on seismic analysis of space structures subjected to multi-dimensional multi-support excitations. However, the research on dynamic reliability of stochastic response is just little. Extreme value distribution (EVD) of dynamic response of stochastic space structures is so necessary to dynamic reliability. Nevertheless, there is no effective approach to obtain EVD as yet. Hence the recently formulated probability density evolution method (PDEM) is adopted to obtain the EVD and subsequently evaluate dynamic reliability of space structure subjected to multi-dimensional multi-support excitations. PDEM can effectively gain the EVD and calculate the dynamic reliability of stochastic structures. To demonstrate the accuracy and efficiency of the PDEM in space structures, a single-layer spherical reticulated dome is extensively researched and the EVD and dynamic reliability is observed and analyzed, respectively. In the present paper five apparent wave velocities and four displacement thresholds in vertical direction are taken into consideration. Compared with the results evaluated by conventional simulation method, the PDEM is of accuracy, efficiency and versatility in space structures.

Seismic wave passage effect on dynamic response of submerged floating tunnels

In this paper, a numerical analysis is performed to investigate the dynamic characteristics of submerged floating tunnels (SFTs) under seismic wave passage effect. The large mass method is examined firstly and then used to simulate numerically the dynamic response of SFTs. It is found that the dynamic response of SFTs is influenced remarkably by the multi-support excitation with the seismic wave passage effect and varies with the velocity of seismic waves in a non-monotone way. The numerical results show that the response under the multi-support excitation is much larger than that under the simultaneous excitation except for the displacement response in some velocities, and there exists a peak velocity of seismic waves that corresponds the maximum response of the structure. In addition, for every velocity, the most remarkable response appears near the shore connection corresponding to output end of the seismic wave. This finding reflects the unique behavior of SFTs under the multi-support excitations and is meaningful to the seismic design of SFTs as well as other periodic long-span structures.

Seismic analysis of a SFT solution for the Messina Strait crossing

In this paper the seismic behaviour of a Submerged Floating Tunnel (SFT) solution for the Messina Strait Crossing is investigated. The Submerged Floating Tunnel (SFT) is an innovative structural solution for the realization of waterway crossings, which features several advantages from the structural, economic and environmental impact points of view. In particular, it seems to be a suitable system for waterway crossings in high seismicity zones, thanks to the deformability of the overall structure. Moreover the interaction with the water provides additional damping and inertia to the structural motion.In order to evaluate the SFT structural response to seismic events, time domain dynamic analyses are carried out considering a ground multi-support excitation scenario determined through the generation of synthetic accelerograms by simulating the fault breaking mechanism. This is important due to the distance among the tunnel supports, also because it can lead to significant excitation of tunnel vibration modes featuring a negligible participating mass, which would not be excited in case of synchronous ground motion. Moreover the propagation of the vertical ground motion into the water and the fluid-structure interaction are taken into account in the analyses. Different structural solutions are considered, mainly differing for the cable system configuration. The dynamic properties of the considered solutions and the main aspects of their structural response are illustrated. The obtained results, although they cannot lead to definitive conclusions, give useful indications about the seismic response of Submerged Floating Tunnels and confirm that such an innovative structural solution for waterway crossings feature great potentialities, in particular when large spans have to be surpassed, such as in the Messina Strait crossing.

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.

Vibration test and analysis of Laoshan bicycle gymnasium for the Olympic Games under multi-support excitations

The vibration tests of Laoshan bicycle gymnasium for the Olympic Games are performed under multi-support excitations in order to verify the effectiveness of multi-support time history method. The excitation sources come from the impact forces acting on the ring beam of the reticulated structure, on the basis of which the records of motions of each excited point and corresponding structural vibration responses are all collected. The theoretical analytical model of the structure is further established and the structural dynamic responses are obtained subjected to the same excitation case via multi-support time history method. The calculation results are generally in agreement with those of the test in both time domain and frequency domain, which verify the effectiveness of multi-support time history method. The vibration test can also provide references for long-span structures under multi-support excitations.

A new spatial coherence model and analytical coefficients for multi-support response spectrum combination

In this paper, a new spatial coherence model of seismic ground motions is proposed by a fitting procedure. The analytical expressions of modal combination (correlation) coefficients of structural response are developed for multi-support seismic excitations. The coefficients from both the numerical integration and analytical solutions are compared to verify the accuracy of the solutions. It is shown that the analytical expressions of numerical modal combination coefficients are of high accuracy. The results of random responses of an example bridge show that the analytical modal combination coefficients developed in this paper are accurate enough to meet the requirements needed in practice. In addition, the computational efficiency of the analytical solutions of the modal combination coefficients is demonstrated by the response computation of the example bridge. It is found that the time required for the structural response analysis by using the analytical modal combination coefficients is less than 1/20 of that using numerical integral methods.

Multi-support excitation of single span bridges, using real seismic ground motion recorded at the SMART-1 array

The real spatial heterogeneity of the ground accelerations in recorded events at the SMART-1 array in Taiwan show more random variation than is assumed by SVEGM type models. Rather than employing some exponential type best-fit for the absolute coherency between two dissimilar spatial locations, real multi-station data from SMART-1 is used to generate a more detailed picture of the spatial heterogeneity present. A novel correction scheme is employed to reprocess the SMART-1 data. This paper considers the errors, in seismically induced forces, that can be accrued if identical support excitation (ISE) analysis is used in place of a multi-support excitation (MSE) analysis. A spectrum of bridge spans and spatial horizontal alignments are investigated using contoured polar response spectra. The effect of structural mode coupling is investigated. The conditions under which an ISE analysis is not conservative are reported.

Seismic design for steel trussed arch to multi-support excitations

The behavior of steel trussed arch to multi-support excitations is studied. The spatial variation of ground motion is modeled by an empirical coherency loss function. Numerical results indicate that horizontal multi-support excitations have a quite large amplification effect on the seismic responses of the trussed arch. This amplification effect cannot be ignored in the seismic design of such structures. Vertical multi-support excitations reduce the seismic responses of the trussed arch. Therefore the assumption that vertical free-field ground motions are spatially uniform is available to assure the degree of seismic safety reliability of the trussed arch. An average response spectrum method is subsequently introduced to calculate the arch response to multi-support excitations. The advantage of the method is that the linear peak seismic response of the arch to multi-support excitations can be obtained as conveniently as the conventional response spectrum method does. The good agreement of results between the time-history method and the average response spectrum method shows the validity of the latter method.

A response spectrum method for seismic response analysis of structures under multi-support excitations

Based on the random vibration theory, a response spectrum method is developed for seismic response analysis of linear, multi-degree-of-freedom structures under multi-support excitations is developed. Various response quantities, including the mean and variance of the peak response, the response mean frequency, are obtained from proposed combination rules in terms of the mean response spectrum. This method makes it possible to apply the response spectrum to the seismic reliability analysis of structures subjected to multi-support excitations. Considering that the tedious numerical integration is required to compute the spectral parameters and correlation coefficients in above combination rules, this paper further offers simplified procedures for their computation, which enhance dramatically the computational efficiency of the suggested method. The proposed procedure is demonstrated for tow numerical examples: (1) two-span continuous beam; (2) two-tower cabled-stayed bridge by using Monte Carlo simulation (MC). For this purpose, this paper also presents an approach to simulation of ground motions, which can take into account both mean and variation properties of response spectrum. Computed results based on the response spectrum method are in good agreement with Monte Carlo simulation results. And compared with the MSRS method, a well-developed multi-support response spectrum method, the proposed method has an incomparable computational efficiency.

다중지점 가진 효과를 고려한 부유식 교량의 지진응답 해석

다중지점 가진 효과를 고려한 부유식 교량의 지진응답 해석

Raman characterization of Ar+ ion-implanted GaN

This paper carries out a parametrical study of the pounding phenomenon associated with the seismic response of multi-span simply supported bridges with base isolation devices. In particular, the analyses focus on the causal relationship between pounding and the properties of a spatially varying earthquake ground motion. In order to include the effect of the torsional component of pounding forces on the seismic response of the whole structure, a three-dimensional (3D) finite element model has been defined and 3D non-linear time-history analyses have been performed. A parametrical study on the size of the gaps between adjacent bridge decks has highlighted that the pounding effects are amplified when the spatially varying ground motion time histories at each support are considered. Because of a spatially varying input, the pounding forces can assume values 3–4 times larger than those derived by a conventional seismic analysis with uniform input or with spatial input but considering ground motion wave passage effect only. The numerical results show that in order to achieve an acceptably safe structural performance during seismic events, a correct design of the isolation devices should take into account the relative displacements calculated by means of a non-linear time-history analysis with multi-support excitation. Copyright © 2002 John Wiley & Sons, Ltd.

Seismic response of multi‐span simply supported bridges to a spatially varying earthquake ground motion

AbstractThis paper carries out a parametrical study of the pounding phenomenon associated with the seismic response of multi‐span simply supported bridges with base isolation devices. In particular, the analyses focus on the causal relationship between pounding and the properties of a spatially varying earthquake ground motion. In order to include the effect of the torsional component of pounding forces on the seismic response of the whole structure, a three‐dimensional (3D) finite element model has been defined and 3D non‐linear time‐history analyses have been performed. A parametrical study on the size of the gaps between adjacent bridge decks has highlighted that the pounding effects are amplified when the spatially varying ground motion time histories at each support are considered. Because of a spatially varying input, the pounding forces can assume values 3–4 times larger than those derived by a conventional seismic analysis with uniform input or with spatial input but considering ground motion wave passage effect only. The numerical results show that in order to achieve an acceptably safe structural performance during seismic events, a correct design of the isolation devices should take into account the relative displacements calculated by means of a non‐linear time‐history analysis with multi‐support excitation. Copyright © 2002 John Wiley & Sons, Ltd.

Nonlinear Response of Bridges under Multisupport Excitation

The authors present the results of an extensive numerical study on the nonlinear response of bridges subjected to multisupport seismic excitation. Bridges of varying stiffness and ductility have been designed for nonsynchronous and synchronous motion, and subsequently, have been analyzed in the nonlinear range under nonsynchronous input motion. The purpose of this investigation was to assess the effects on the peak inelastic response of bridge structures and the extent of validity of the force reduction factor (q-factor) approach for the design. Findings revealed that displacement ductility demands in bridges designed by the q-factor method for a multisupport excitation were in good agreement with the chosen value of q. The bridges designed for synchronous input and then examined for nonsynchronous motion displayed an excess of strength in the central piers, whereas the opposite happened for those near the abutments, which may have displacement ductility demands larger than those requested under synchronous motion.

An efficient analysis of structural response for multiple-support seismic excitations

A response spectrum method is proposed for the seismic analysis of a multisupport structure subjected to spatially varying ground motion. Based on theoretical results by Der Kiureghian and Hofer, an approximate and efficient analysis of the frequency integral of the cross-correlation function of multisupport excitation is presented. A two-span beam-like structure is studied to demonstrate the application of this proposed method and to characterize the influence of the differential support motion. Treatment of the various combinations of phase relationships between supports is also discussed.

Torsional Effect in Soil-Structure Interaction

A simplified method to evaluate the dynamic response of a building, including the wave propagation effects of ground motion is described. This method is based on a computer code that can calculate the dynamic response of buildings subject to multisupport excitation given impedance data calculated by other methods. Only linear systems and symmetrical structure are considered. The soil-structure interaction effect is accounted for by including in the dynamic model, the compliance functions of the soil medium. The computer capability required is widely available within the nuclear industry. The study concluded that within the assumptions made and analytical models considered, the practical solution scheme adopted in this study by applying earthquake input motion sequentially at nodal points on the foundations seems to be simple to use in the investigation of translational and torsional structure responses subjected to the traveling wave effect of seismic ground motion. Also, the soil-structure interaction effect may be important in calculating translational and torsional responses due to the traveling wave effect of earthquake excitation.