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1.
A stochastic approach has been formulated for the linear analysis of suspension bridges subjected to earthquake excitations. The transfer functions of various responses have been formulated while including the effects of dynamic Soil–Structure Interaction (SSI) via the use of the fixed-base modes of the structure. The excitation has been characterized by the ‘equivalent stationary’ processes corresponding to the free-field motions at each support and by an assumed coherency function between these motions. The proposed formulation considers the non-stationarity in the structural response due to sudden application of excitation by considering (i) the time-dependent frequency response functions, and (ii) the order statistics formulation for the peak factors in evolutionary response processes. The formulation has been illustrated by analysing the seismic response of the Golden Gate Bridge at San Francisco for two example excitations conforming to USNRC-specified design spectra. The significance of various governing parameters on the dynamic soil–structure interaction effects on the seismic response of suspension bridges has also been studied. It has been found that the contribution of the vertical component of ground motion to the bridge response increases with increasing soil compliance. Also, the extent to which the spatial variation of ground motion affects the bridge response depends on how significant the SSI effects are. Copyright © 1999 John Wiley & Sons Ltd. 相似文献
2.
本文推导了基于位移激励计算单自由度体系拟速度谱公式,通过构造的脉冲位移时程对公式精度进行了验证;之后利用小波变换去除强震记录噪声而保留地震动永久位移,再基于去趋势项方法和滤波方法去除永久位移后,计算拟速度谱。算例结果表明:短周期段内,不保留永久位移的位移激励拟速度谱值与保留永久位移的位移激励拟速度谱值相差很小;中长周期段内,不保留永久位移的位移激励拟速度谱值总体上小于保留永久位移的位移激励拟速度谱值,且不保留永久位移时,滤波方法引起的拟速度谱降幅大于去趋势项方法所引起的拟速度谱降幅。因此,基于位移激励计算中长周期结构的地震反应时,应保留地震动永久位移,或基于去趋势项方法去除永久位移。 相似文献
3.
考虑土-结构相互作用双层柱面网壳在多点输入下的地震反应分析 总被引：3，自引：0，他引：3
目前对于网壳结构的地震反应研究大部分仍然采用一致输入,特别是没有考虑土-结构相互作用对网壳结构的影响。本文通过对大型有限元分析软件MSC.Nastran的二次开发,用等效线性化方法考虑土体的非线性,对土体采用三维实体单元建模,并对土体在基岩面上采用地震动的多点输入,计算分析了大跨度双层柱面网壳的动力反应,并且与一致地震动输入下网壳结构的地震反应进行了对比,考察了两者之间的差异,深入分析了考虑土-结构相互作用下,双层柱面网壳结构在多点输入和一致输入下的地震反应规律,并得出了一些重要结论。 相似文献
4.
A 40-m thick clay deposit was subjected to sinusoidal excitations using a foundation block and an eccentric mass type vibrator. The response of the foundation block and the surrounding soil was measured using geophones inside the soil and on the surface. The phase shift between the excitation signal and the response signal, the accelerations of the foundation block and the particle velocities in the soil are compared with those obtained from a frequency-dependent numerical model based on the exact analytical solution for the boundary value problem of a rectangular foundation resting on a linear elastic halfspace. 相似文献
5.
Seismic performance and dynamic response of bridge–embankments during strong or moderate ground excitations are investigated through finite element (FE) modelling and detailed dynamic analysis. Previous research studies have established that bridge–embankments exhibit increasingly flexible performance under high‐shear deformation levels and that soil displacements at bridge abutment supports may be significant particularly in the transverse direction. The 2D equation of motion is solved for the embankment, in order to evaluate the dynamic characteristics and to describe explicitly the seismic performance and dynamic response under transverse excitations accounting for soil nonlinearities, soil–structure interaction and imposed boundary conditions (BCs). Using the proposed model, equivalent elastic analysis was performed so as to evaluate the dynamic response of approach embankments while accounting for soil–structure interaction. The analytical procedures were applied in the case of a well‐documented bridge with monolithic supports (Painter Street Overcrossing, PSO) which had been instrumented and embankment participation was identified from its response records after the 1971 San Fernando earthquake. The dynamic characteristics and dynamic response of the PSO embankments were evaluated for alternative BCs accounting for soil–structure interaction. Explicit expressions for the evaluation of the critical embankment length Lc are provided in order to quantify soil contribution to the overall bridge system under strong intensity ground excitations. The dynamic response of the entire bridge system (deck–abutments–embankments) was also evaluated through simplified models that considered soil–structure interaction. Results obtained from this analysis are correlated with those of detailed 3D FE models and field data with good agreement. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
6.
A convex model is used to estimate the maximum response of structural systems subjected to uncertain seismic excitations. The convex model is based on the assumption that the energy of the excitation is bounded . A reduction factor, defined in the modal domain by dividing the results obtained from the convex model by those from the time history of the actual record, is used to calibrate the convex model. An average reduction factor is also defined by averaging a set of excitation-specific reduction factors. The average reduction factor can be used for unknown excitations with an assumed energy bound and certain common earthquake characteristics. These common characteristics can be defined either by a set of previous earthquakes in the region or by regional earthquake spectra. The convex model using the average reduction factor yields acceptable predictions of the maximum response. 相似文献
7.
为了考察外部激励群延时对反应谱的影响,分别从确定性的角度和统计的角度分析了群延时对线性单自由度结构体系位移响应最大值的影响。推导出了对应于给定单自由度结构体系在任意外部激励作用下最大位移响应的群延时。据此可以利用任意外部激励的群延时与结构体系的最大位移响应群延时的关系评估体系在该外部激励作用下位移响应峰值的大小。统计分析的结果表明:激励群延时的均值和方差对结构体系位移响应最大值的影响具有明显的规律性;激励群延时的分布频数与结构体系最大位移响应之间也存在着显著的关系。 相似文献
8.
A stochastic critical excitation is defined as that excitation with a given variance that maximizes the variance in the dynamic response of a system. A non-stationary filtered shot noise is used to develop a stochastic critical excitation model of an earthquake ground motion process, and the response statistics for a linear system are determined in both time and frequency domains. The sensitivity of response to several assumed earthquake pulse arrival rate functions is examined. Responses to recorded strong ground motion and to stochastic critical excitations with the same total energy are compared to assess the degree of conservatism in the procedure. An application of the procedure to seismic qualification of equipment is presented. 相似文献
9.
Elias G. Dimitrakopoulos Nicos Makris Andreas J. Kappos 《Bulletin of Earthquake Engineering》2011,9(2):561-579
In this paper the seismic response of inelastic structures with unilateral contact is revisited with dimensional analysis.
All physically realizable contact types are captured via a non-smooth complementarity approach. The implementation of formal
dimensional analysis leads to a condensed presentation of the response and unveils remarkable order even though two different
types of non-linearity coexist in the response: the boundary non-linearity of unilateral contact and the inelastic behaviour
of the structure itself. It is shown that regardless the intensity and frequency content of the excitation, all response spectra
become self-similar when expressed in the appropriate dimensionless terms. The proposed approach hinges upon the notion of
the energetic length scale of an excitation which measures the persistence of ground shaking to impose deformation demands.
Using the concept of persistency which is defined for excitations with or without distinct pulses, the response is scaled
via meaningful novel intensity measures: the dimensionless gap and the dimensionless yield displacement. The study confirms
that contact may have a different effect on the response displacements of inelastic structures depending on the spectral region.
In adjacent inelastic structures, such as colliding buildings or interacting bridge segments, contact is likely to alter drastically
the excitation frequencies’ at which the system is most vulnerable. Finally, it is shown that the proposed approach yields
maximum response displacements which correlate very well with the persistency of real earthquakes for a bridge system with
considerably complex behaviour. 相似文献
10.
This paper presents a static equivalent approach to estimate the maximum kinematic interaction effects on piles subjected to lateral seismic excitation. Closed-form expressions are reported for the evaluation of the maximum free-field soil movements and for the computation of maximum pile shear force and bending moments. Firstly, modal analysis, combined with a suitable damped response spectrum, is used to evaluate the maximum free-field response. Secondly, the pile is schematised as a Winkler's beam subjected to equivalent static forces defined according to soil vibration modal shapes and amplitude. The method may be applied by using response spectra suggested by National Standards or those obtained with accelerograms. The procedure proposed may be conveniently implemented in simple spreadsheets or in commercial finite element programs and easily used by practicing engineers. Method accuracy is demonstrated by comparing the results with those obtained with a more rigorous model. Good results may be achieved by considering only the first soil vibration mode making the procedure straightforward for practical design purposes. 相似文献
11.
12.
The seismic response of two fundamental mechanical configurations of earthquake engineering, the elastic–plastic system and the pounding oscillator, is revisited with the aid of dimensional analysis. Starting from the previous work of the authors which focused on pulse-type excitations, the paper offers an alternative, yet physically motivated, way to present the response of yielding and pounding structures under excitations with arbitrary time history. It is shown, that when the appropriate time and length scales are adopted, dimensional analysis can be implemented and remarkable order emerges in the response. Regardless of the acceleration level and frequency content of the excitation, all response spectra become self-similar and when expressed in dimensionless terms, resulting from dimensional analysis, follow a single master curve. The study proposes such scales together with the associated selection criteria among the available in literature strong ground motion parameters and shows that the proposed approach reduces drastically the scatter in the response. 相似文献
13.
Vertical earthquake response of megawatt‐sized wind turbine with soil‐structure interaction effects 
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下载免费PDF全文 The 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. 相似文献
14.
Two practical approaches, response spectrum and time-history methods, are developed to evaluate the response of flexible multi-degree-of-freedom (MDF) systems, notably long-span bridges, to multiple-support seismic excitations. For practical convenience, ground motions within a group of adjacent supports on continuous soil or rock are assumed to be uniform and synchronized, while those of different groups are treated as non-uniform and uncorrelated. The response spectrum analysis is extended to include the cross-correlation of modal responses, which prove important when closely spaced modal frequencies exist. An example of the significance of multiple-support excitations is illustrated by application to a suspension bridge. Qualitatively comparable effects can be expected for other bridges of similar type or dimensions. 相似文献
15.
Dynamic response of a flexible cantilever wall retaining elastic soil to harmonic transverse seismic excitations is determined with the aid of a modified Vlasov–Leontiev foundation model and on the assumption of vanishing vertical displacement of the soil medium. The soil–wall interaction is taken into consideration in the presented model. The governing equations and boundary conditions of the two unknown coupled functions in the model are derived in terms of Hamilton׳s principle. Solutions of the two unknown functions are obtained on the basis of an iterative algorithm. The present method is verified by comparing its results with those of the existing analytical solution. Moreover, a mechanical model is proposed to evaluate the presented method physically. A parametric study is performed to investigate the effects of the soil–wall system properties and the excitations on the dynamic response of the wall. 相似文献
16.
A simplified multisupport response spectrum method is presented.The structural response is a sum of two components of a structure with a first natural period less than 2 s.The first component is the pseudostatic response caused by the inconsistent motions of the structural supports,and the second is the structural dynamic response to ground motion accelerations.This method is formally consistent with the classical response spectrum method,and the effects of multisupport excitation are considered for any modal response spectrum or modal superposition.If the seismic inputs at each support are the same,the support displacements caused by the pseudostatic response become rigid body displacements.The response spectrum in the case of multisupport excitations then reduces to that for uniform excitations.In other words,this multisupport response spectrum method is a modification and extension of the existing response spectrum method under uniform excitation.Moreover,most of the coherency coefficients in this formulation are simplified by approximating the ground motion excitation as white noise.The results indicate that this simplification can reduce the calculation time while maintaining accuracy.Furthermore,the internal forces obtained by the multisupport response spectrum method are compared with those produced by the traditional response spectrum method in two case studies of existing long-span structures.Because the effects of inconsistent support displacements are not considered in the traditional response spectrum method,the values of internal forces near the supports are underestimated.These regions are important potential failure points and deserve special attention in the seismic design of reticulated structures. 相似文献
17.
A formulation has been proposed for the transfer function of a secondary system response while the primary system is supported on a compliant soil and the excitation comprises of translational ground motion at its base. For this purpose, the earlier formulation of the authors for the fixed-base case, which exactly considers the interaction between the two sub-systems and is based on the use of their individual modal properties, has been extended. Also, the concept of modifying the input excitation for the interaction accelerations (associated with the soil–structure interaction) has been used. An example P–S system and three example earthquake excitations have been considered to illustrate the proposed formulation and to estimate the expected response peak amplitudes in the secondary system. This study shows that ‘detuning’ of the tuned systems may occur in case of significant soil–structure interaction. Further, for the reasons of both safety and economy, ignoring the interaction effects in designing the secondary systems may not always be justified. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
18.
Soil effects on peak ground acceleration, velocity and elastic response spectra (5% damping) are expressed by simple approximate relations in terms of five key parameters: (a) the fundamental vibration period of the non‐linear soil, TS, (b) the period of a bedrock site of equal thickness, Tb, (c) the predominant excitation period, Te, (d) the peak seismic acceleration at outcropping bedrock, a, and (e) the number of significant excitation cycles, n. Furthermore, another relation is proposed for the estimation of TS in terms of the soil thickness H, the average shear wave velocity of the soil V?S,o and a. The aforementioned parameters were first identified through a simplified analytical simulation of the site excitation. The multivariable approximate relations were then formulated via a statistical analysis of relevant data from more than 700 one‐dimensional equivalent‐linear seismic ground response analyses, for actual seismic excitations and natural soil conditions. Use of these relations to back‐calculate the numerical results in the database gives an estimate of their error margin, which is found to be relatively small and unbiased. The proposed relations are also independently verified through a detailed comparison with strong motion recordings from seven well‐documented case studies: (a) two sites in the San Fernando valley during the Northridge earthquake, and (b) five different seismic events recorded at the SMART‐1 accelerometer array in Taiwan. It is deduced that the accuracy of the relations is comparable to that of the equivalent‐linear method. Hence, they can be readily used as a quick alternative for routine applications, as well as for spreadsheet computations (e.g. GIS‐aided seismic microzonation studies) where numerical methods are cumbersome to implement. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
19.
B. K. Maheshwari K. Z. Truman M. H. El Naggar P. L. Gould 《Soil Dynamics and Earthquake Engineering》2004,24(4):343-356
A three-dimensional method of analysis is presented for the seismic response of structures constructed on pile foundations. An analysis is formulated in the time domain and the effects of material nonlinearity of soil on the seismic response are investigated. A subsystem model consisting of a structure subsystem and a pile-foundation subsystem is used. Seismic response of the system is found using a successive-coupling incremental solution scheme. Both subsystems are assumed to be coupled at each time step. Material nonlinearity is accounted for by incorporating an advanced plasticity-based soil model, HiSS, in the finite element formulation. Both single piles and pile groups are considered and the effects of kinematic and inertial interaction on seismic response are investigated while considering harmonic and transient excitations. It is seen that nonlinearity significantly affects seismic response of pile foundations as well as that of structures. Effects of nonlinearity on response are dependent on the frequency of excitation with nonlinearity causing an increase in response at low frequencies of excitation. 相似文献
20.
Estimation of lateral displacement and acceleration responses is essential to assess safety and serviceability of high-rise buildings under dynamic loadings including earthquake excitations. However, the measurement information from the limited number of sensors installed in a building structure is often insufficient for the complete structural performance assessment. An integrated multi-type sensor placement and response reconstruction method has thus been proposed by the authors to tackle this problem. To validate the feasibility and effectiveness of the proposed method, an experimental investigation using a cantilever beam with multi-type sensors is performed and reported in this paper. The experimental setup is first introduced. The finite element modelling and model updating of the cantilever beam are then performed. The optimal sensor placement for the best response reconstruction is determined by the proposed method based on the updated FE model of the beam. After the sensors are installed on the physical cantilever beam, a number of experiments are carried out. The responses at key locations are reconstructed and compared with the measured ones. The reconstructed responses achieve a good match with the measured ones, manifesting the feasibility and effectiveness of the proposed method. Besides, the proposed method is also examined for the cases of different excitations and unknown excitation, and the results prove the proposed method to be robust and effective. The superiority of the optimized sensor placement scheme is finally demonstrated through comparison with two other different sensor placement schemes: the accelerometer-only scheme and non-optimal sensor placement scheme. The proposed method can be applied to high-rise buildings for seismic performance assessment. 相似文献