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1.
The problem of the dynamic response of rigid embedded foundations subjected to the action of external forces and seismic excitation is analysed. It is shown that to calculate the response of rigid embedded foundations, or the response of flat rigid foundations subjected to non-vertically incident seismic waves, it is necessary to obtain not only the impedance matrix for the foundation, but also the forces induced by the incident seismic waves. Under these general conditions, rocking and torsional motion of the foundation is generated in addition to translation. The case of a two-dimensional rigid foundation of semi-elliptical cross-section is used as an example to illustrate the effects of the embedment depth and angle of incidence of the seismic waves on the response of the foundation. 相似文献
2.
大跨度空间网格结构多维多点随机地震反应分析 总被引：4，自引：0，他引：4
本文建立了三维正交地震动多点激励下大跨度空间网格结构的随机地震反应分析方法,依据现行抗震设计规范的有关规定,确定了平稳随机地震动功率谱密度的模型参数。数值仿真分析了一柱距80m的正方形平板网架分别在一维地震动或三维地震动的一致激励、行波激励和考虑部分相干效应的随机激励下的地震反应。结果表明:考虑地震动的空间效应会很大程度地改变结构杆件的内力,其中控制杆件的内力增幅达到30%;地震动的行波效应对结构杆件内力的影响比随机地震动的部分相干效应的影响更大;三维地震作用比一维地震作用下结构杆件的内力大。由此得出结论,对于大跨度空间网格结构,必须进行多维多点地震激励下的随机地震反应分析。 相似文献
3.
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
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5.
A study is made of the harmonic response of a rigid massless rectangular foundation bonded to an elastic half-space and subjected to the action of both external forces and obliquely incident plane seismic waves. The associated mixed boundary value problem is discretized and solved numerically. The results obtained indicate that the angle of incidence of the seismic wave has a marked effect on the nature and magnitude of the foundation response. 相似文献
6.
In this paper a comprehensive investigation on the dynamic characteristics of turbine–generator–foundation systems is performed. All the major components of the system, including turbine–generator casing, shaft, rotors, journal bearings, deck, piers, foundation mat, piles, and soil medium, have been included. Full interaction between the turbine–generator set, the foundation superstructure, and the soil medium, is considered. A hybrid method is used to establish the mathematical model for the turbine–generator-foundation system. The analysis is conducted in the frequency domain through complex frequency response analysis. The response in the time domain is obtained by Fourier transform. The seismic excitation is represented as the control motion on the ground surface, which is generated as an artificial earthquake. A 300 MW turbine-generator-foundation system is analysed under excitations from rotor unbalances and earthquakes. The influence of turbine-generator casing and soil anisotropy on the response of the system is explored. It is found that the presence of casing and soil anisotropy strongly influences the displacements and internal forces of the system under rotor unbalance excitation. Under seismic excitation, however, although the presence of casing and soil anisotropy does affect the displacements of the system, their effect on the internal forces of the system is minimal. 相似文献
7.
This paper presents the results of an experimental work in order to evaluate the performance of a novel proposed retrofitting technique on a typical dome‐roof adobe building by shaking table tests. For this purpose, two specimens, scaled 2:3, were subjected to a total of nine shaking table tests. The unretrofitted specimen, constructed by common practice, is designed to evaluate seismic performance and vulnerability of dome‐roof adobe houses. The retrofitted specimen, exactly duplicating the first specimen, is retrofitted based on the results obtained from unretrofitted specimen tests, and the improvement in seismic behavior of the structure is investigated. Zarand earthquake (2005) Chatrood Station is selected as the input ground motion that was applied consecutively at 25, 100, 125, 150 and 175% of the design‐level excitation. At 125% excitation level, the roof of the unretofitted specimen collapsed due to the walls' out‐of‐plane action and imbalanced forces. The retrofitting elements consist of eight horizontal steel rods drilled into the walls, passed through the specimen and bolted on the opposite wall surfaces. To improve walls in‐plane seismic performance, welded steel mesh without using mortar, covered less than half area of walls on the external face of the walls, is used. In addition to strain gauges for recording steel rod responses, several instrumentations including acceleration and displacement transducers are implemented to capture response time histories of different parts of the specimens. The corresponding full‐scaled retrofitted prototype tolerated peak acceleration of 0.62 g almost without any serious damage. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
8.
地震动差动作用下大跨度空间网壳结构的反应分析 总被引：1，自引：0，他引：1
选取100m跨度的双层柱面网壳结构为研究对象,采用时程分析法,分别进行了结构在单向和三向地震行波输入作用下的反应分析,并针对多种视波速情况进行了研究,考查了地震动不同输入情况下结构杆件内力的分布特点,对其进行了对比分析,为大跨网壳结构的抗震设计提供了理论依据。研究表明,考虑行波效应会使结构部分构件内力有一定程度的提高,多维地震作用比单维地震作用下结构的杆件内力大。由此得出结论：对于大跨度空间网壳结构,应该进行多维非一致输入下的地震反应分析;为保证抗震安全,应对可能出现的地面视波速进行全面分析。 相似文献
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10.
拱桥在竖向地震波输入下的行波共振现象 总被引：1，自引：0，他引：1
以某大跨公路拱桥为例讨论了行波作用对拱桥地震反应的影响机理.采用有限元程序计算分析了该拱桥在竖向地震动行波输入和一致输入下的动力反应,通过结果对比反映出行波地震反应并不简单随波速单调变化的现象.经过分析进一步提出了行波共振的概念,阐述了行波共振效应的产生机理.数值分析结果表明了考虑行波效应对大跨拱桥地震反应分析的重要性. 相似文献
11.
A generalized pushover analysis (GPA) procedure is developed for estimating the inelastic seismic response of structures under earthquake ground excitations. The procedure comprises applying different generalized force vectors separately to the structure in an incremental form with increasing amplitude until a prescribed seismic demand is attained for each generalized force vector. A generalized force vector is expressed as a combination of modal forces, and simulates the instantaneous force distribution acting on the system when a given response parameter reaches its maximum value during dynamic response to a seismic excitation. While any response parameter can be selected arbitrarily, generalized force vectors in the presented study are derived for maximum interstory drift parameters. The maximum value of any other response parameter is then obtained from the envelope of GPAs results. Each nonlinear static analysis under a generalized force vector activates the entire multi‐degree of freedom effects simultaneously. Accordingly, inelastic actions develop in members with the contribution of all ‘instantaneous modes’ in the nonlinear response range. Target seismic demands for interstory drifts at the selected stories are calculated from the associated drift expressions. The implementation of the proposed GPA is simpler compared with nonlinear response history analysis, whereas it is less demanding in computational effort when compared with several multi‐mode adaptive nonlinear static procedures. Moreover, it does not suffer from the statistical combination of inelastic modal responses obtained separately. The results obtained from building frames have demonstrated that GPA is successful in estimating maximum member deformations and member forces with reference to the response history analysis. When the response is linear elastic, GPA and response spectrum analysis produce identical results. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
12.
The possibility of controlling the seismic response of tall buildings by use of a structural system consisting of a stiff and lightly damped external structure and a very flexible and moderately damped internal structure connected by stiff links at a few elevations is explored. Optimal damping values for the internal structure are obtained by consideration of the response on the composite structure in the vicinity of its fundamental mode. The resulting optimal damping values depend on the relative stiffness of both structures. Numerical results in the frequency and time domain are used to illustrate the advantages of such a system for seismic excitation. The possibility of using flexible links between the internal and external structures to moderate the required reduction of stiffness in the internal structure is also explored. © 1998 John Wiley & Sons, Ltd. 相似文献
13.
A nonlinear static analysis methodology for the derivation of a set of pushover curves for any angle of incidence of the seismic action (multidirectional pushover curves) for bridges is developed, wherein the interaction between axial force and biaxial moments at critical pier sections or biaxial shear forces at the bearings is taken into account. Dynamic pushover curves (base shear vs. peak deck displacement) for arbitrary angle of incidence of the excitation, are derived for both unidirectional (single-component) and bidirectional (dual-component) ground motion. It is found that neglecting the minor horizontal component leads to underestimation of bridge response, especially along the bridge principal directions and that the angle of incidence of bidirectional excitation affects bridge response, but to a lesser extent than in the case of unidirectional excitation. The proposed procedure is then applied to a straight symmetric bridge, its results are checked against those from response-history analysis, and is found to be sufficiently accurate for practical application. Using the derived results it is also found that the design of the selected bridge is safe since for the design bidirectional earthquake the bridge starts to behave inelastically (the first plastic hinge forms), while its failure occurs for about four times the design seismic action. 相似文献
14.
Tunnels are commonly designed under seismic loading assuming “free field conditions”. However, in urban areas these structures pass beneath buildings, often high-rise ones, or are located close to them. During seismic excitation, above ground structures may cause complex interaction effects with the tunnel, altering its seismic response compared to the “free field conditions” case. The paper summarizes an attempt to identify and understand these interaction effects, focusing on the tunnel response. The problem is investigated in the transversal direction, by means of full dynamic time history analyses. Two structural configurations are studied and compared to the free field conditions case, consisting of one or two above ground structures, located over a circular tunnel. Above ground structures are modeled in a simplified way as equivalent single-degree of freedom oscillators, with proper mechanical properties. Several parameters that are significantly affecting the phenomenon are accounted for in this parametric study, namely the soil to tunnel relative flexibility, the tunnel dimensions, the tunnel burial depth and the soil properties and nonlinearities during shaking. Tunnels response characteristics are compared and discussed, in terms of acceleration, deformations and lining dynamic internal forces. Internal forces are also evaluated with analytical closed form solutions, commonly used in preliminary stages of design, and compared with the numerical predictions. The results indicate that the presence of the above ground structures may have a significant effect on the seismic response of the tunnel, especially when the latter is stiff and located in shallow depths. 相似文献
15.
《地震工程与工程振动(英文版)》2015,(3)
The pseudo excitation method(PEM) has been improved into a more practical form,on which the analytic formulae of seismic response power spectral density(PSD) of simplified large-span structural models have been derived.The analytic formulae and numerical computing results of seismic response PSD have been derived to study the mechanism of multi-support excitation effects,such as the wave-passage effect and incoherence effect,for the seismic response of multiand large-span structures.By using a multi-span truss as an example,the influence of multi-support excitation effects on the seismic response of such structures is studied. 相似文献
16.
Shehata E. Abdel Raheem 《Bulletin of Earthquake Engineering》2014,12(4):1705-1724
Post-earthquake damages investigation in past and recent earthquakes has illustrated that the building structures are vulnerable to severe damage and/or collapse during moderate to strong ground motion. Among the possible structural damages, seismic induced pounding has been commonly observed in several earthquakes. A parametric study on buildings pounding response as well as proper seismic hazard mitigation practice for adjacent buildings is carried out. Three categories of recorded earthquake excitation are used for input excitations. The effect of impact is studied using linear and nonlinear contact force model for different separation distances and compared with nominal model without pounding consideration. The severity of the impact depends on the dynamic characteristics of the adjacent buildings in combination with the earthquake characteristics. Pounding produces acceleration and shear forces/stresses at various story levels that are greater than those obtained from the no pounding case, while the peak drift depends on the input excitation characteristics. Also, increasing gap width is likely to be effective when the separation is sufficiently wide to eliminate contact. Furthermore, it is effective to provide a shock absorber device system for the mitigation of impact effects between adjacent buildings with relatively narrow seismic gaps, where the sudden changes of stiffness during poundings can be smoothed. This prevents, to some extent, the acceleration peaks due to impact. The pounding forces exerted on the adjacent buildings can be satisfactorily reduced. 相似文献
17.
双向偏心结构扭转耦联地震反应的序列最优控制 总被引：1，自引：0，他引：1
本文分析了不对称建筑结构平移-扭转耦联振动的动力特性及地震作用下的响应;根据地震动输入结构的过程,推导出一种更为一般的最优控制算法,所获得的控制力表达式同时包括地震响应和地震激励。通过对一非规则四层框架结构的扭转耦联地震反应控制分析表明,该算法不仅能有效地控制结构的平移地震反应,而且更有效地抑制结构的扭转耦联地震反应。 相似文献
18.
地震动空间效应对大跨度桥梁非线性地震响应的影响 总被引：1，自引：1，他引：0
由于大跨度桥梁的桥墩间距离较大,其地震响应分析应考虑地震动输入的空间效应。本文建立了多点激励下大跨度桥梁地震响应分析方法,采用损伤塑性本构模型模拟混凝土材料特性,考虑地震动空间效应对大跨度连续刚构桥进行非线性地震响应分析,从而分析地震动空间效应对大跨度桥梁地震响应的影响。研究表明:考虑行波激励或多点激励时桥梁地震响应较一致激励而言有所差异,考虑地震动空间效应时可能会夸大或减小桥梁结构的动力响应;多点激励时桥梁地震响应会随视波速的改变而变化。由此得出结论,对于大跨度桥梁地震响应分析应合理的考虑地震动空间效应。 相似文献
19.
Two equivalent semi-discrete formulations are presented for the problem of the transient response of soil-structure interaction systems to seismic excitation, considering linear behaviour of the soil material and arbitrary non-linear structural properties. One formulation results in a direct method of analysis in which the motion in the structure and the entire soil medium, rendered finite by an artificial absorbing boundary, is determined simultaneously. The other represents a substructuring technique in which the structure and the soil are analysed separately. The forces induced in the discretized system by the incident seismic motion are obtained as part of the general formulation by using the free-field motion of the unaltered soil as the earthquake input. It is shown that these forces act within the soil region in the direct method, but only on the soil-structure interface in the substructure formulation. Both sets of forces, however, involve only the displacements and tractions acting on the fictitious surface in the unaltered (linear) soil which coincides with the soil-structure interface of the complete system. It is shown, further, that the free-field displacements alone define a minimal set of data for evaluating the seismic response of the structure, since the tractions and displacements on that surface are interrelated. In practice, the minimal set must be obtained by extrapolating the available information, as the free-field ground motion at a site is usually specified at a single reference point. 相似文献
20.
为研究卵石土场地地震反应特征,基于四川成都典型卵石土场地,通过振动台模型试验研究卵石土场地在不同地震波、不同地震强度激励下的加速度峰值放大系数、加速度频谱反应及动土压力反应,并且对其场地地震反应非线性效应及土体动剪应力-动剪应变关系进行分析。结果表明：卵石土场地表层土层对地震波具有明显的放大效应,加速度峰值放大系数介于1～1.4之间,下部土层放大效应较小,加速度峰值放大系数介于0.9～1.2之间。卵石土场地对地震波具有低频放大,高频滤波的作用,滤波频率上、下限随激励强度的增大逐渐向低频方向移动。激励强度较小时,土体尚未破坏,动土压力在地震过程中逐渐增大;随着激励强度的增大,动土压力反应明显增大,表现出骤减后逐渐增大的现象。在激励强度较小时(SN1),中部土体最先进入非线性反应阶段,地震波在中部土层能量损耗最大;激励强度较大时(EL3),土体均发生了较大变形,土体最大动剪应变达到1.7%,此时卵石土场地对地震波的放大作用明显减弱。 相似文献