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1.
An approximate method for linear analysis of asymmetric‐plan, multistorey buildings is specialized for a single‐storey, base‐isolated structure. To find the mode shapes of the torsionally coupled system, the Rayleigh–Ritz procedure is applied using the torsionally uncoupled modes as Ritz vectors. This approach reduces to analysis of two single‐storey systems, each with vibration properties and eccentricities (labelled ‘effective eccentricities’) similar to corresponding properties of the isolation system or the fixed‐base structure. With certain assumptions, the vibration properties of the coupled system can be expressed explicitly in terms of these single‐storey system properties. Three different methods are developed: the first is a direct application of the Rayleigh–Ritz procedure; the second and third use simplifications for the effective eccentricities, assuming a relatively stiff superstructure. The accuracy of these proposed methods and the rigid structure method in determining responses are assessed for a range of system parameters including eccentricity and structure flexibility. For a subset of systems with equal isolation and structural eccentricities, two of the methods are exact and the third is sufficiently accurate; all three are preferred to the rigid structure method. For systems with zero isolation eccentricity, however, all approximate methods considered are inconsistent and should be applied with caution, only to systems with small structural eccentricities or stiff structures. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
2.
This paper presents an efficient procedure to determine the natural frequencies, modal damping ratios and mode shapes for torsionally coupled shear buildings using earthquake response records. It is shown that the responses recorded at the top and first floor levels are sufficient to identify the dominant modal properties of a multistoried torsionally coupled shear building with uniform mass and constant eccentricity even when the input excitation is not known. The procedure applies eigenrealization algorithm to generate the state‐space model of the structure using the cross‐correlations among the measured responses. The dynamic characteristics of the structure are determined from the state‐space realization matrices. Since the mode shapes are obtained only at the instrumented floor (top and first floors) levels, a new mode shape interpolation technique has been proposed to estimate the mode shape coefficients at the remaining floor levels. The application of the procedure has been demonstrated through a numerical experiment on an eight‐storied torsionally coupled shear building subjected to earthquake base excitation. The results show that the proposed parameter identification technique is capable of identifying dominant modal parameters and responses even with significant noise contamination of the response records. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
3.
An Erratum has been published for this article in Earthquake Engng. Struct. Dyn. 2004; 33:1429. Based on structural dynamics theory, the modal pushover analysis (MPA) procedure retains the conceptual simplicity of current procedures with invariant force distribution, now common in structural engineering practice. The MPA procedure for estimating seismic demands is extended to unsymmetric‐plan buildings. In the MPA procedure, the seismic demand due to individual terms in the modal expansion of the effective earthquake forces is determined by non‐linear static analysis using the inertia force distribution for each mode, which for unsymmetric buildings includes two lateral forces and torque at each floor level. These ‘modal’ demands due to the first few terms of the modal expansion are then combined by the CQC rule to obtain an estimate of the total seismic demand for inelastic systems. When applied to elastic systems, the MPA procedure is equivalent to standard response spectrum analysis (RSA). The MPA estimates of seismic demand for torsionally‐stiff and torsionally‐flexible unsymmetric systems are shown to be similarly accurate as they are for the symmetric building; however, the results deteriorate for a torsionally‐similarly‐stiff unsymmetric‐plan system and the ground motion considered because (a) elastic modes are strongly coupled, and (b) roof displacement is underestimated by the CQC modal combination rule (which would also limit accuracy of RSA for linearly elastic systems). Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
4.
A generalized multi‐mode pushover analysis procedure was developed for estimating the maximum inelastic seismic response of symmetrical plan structures under earthquake ground excitations. Pushover analyses are conducted with story‐specific generalized force vectors in this procedure, with contributions from all effective modes. Generalized pushover analysis procedure is extended to three‐dimensional torsionally coupled systems in the presented study. Generalized force distributions are expressed as the combination of modal forces to simulate the instantaneous force distribution acting on the system when the interstory drift at a story reaches its maximum value during seismic response. Modal contributions to the generalized force vectors are calculated by a modal scaling rule, which is based on the complete quadratic combination. Generalized forces are applied to the mass centers of each story incrementally for producing nonlinear static response. Maximum response quantities are obtained when the individual frames attain their own target interstory drift values in each story. The developed procedure is tested on an eight‐story frame under 15 ground motions, and assessed by comparing the results obtained from nonlinear time history analysis. The method is successful in predicting the torsionally coupled inelastic response of frames responding to large interstory drift demands. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
5.
A method to determine the approximate normal modes and the modal damping for torsionally coupled buildings on an elastic foundation is presented. The modal damping is determined by an iterative procedure which matches the approximate normal mode solution with the rigorous solution. The response quantity to be matched is selected in a consistent and logical manner. The normal modes and the damping ratios thus found are then used to determine the seismic response of the interaction system by the response spectrum technique. 相似文献
6.
The application of perturbation analysis in torsionally coupled buildings makes it possible to obtain an approximation of the dynamic properties of the buildings in question by combining appropriately the dynamic properties of the corresponding torsionally uncoupled buildings. This note aims to clarify the results obtained from a second-order perturbation analysis of the mode shapes of torsionally coupled buildings. Numerical examples of building models are given to illustrate the theoretical points. 相似文献
7.
In most of the research work on structural vibration control only two‐dimensional plane structural modelling has been considered, although only a few practical building structures can be modelled as planar structures. Therefore, these methods are not directly applicable to the majority of the practical building structures. This paper discusses the design of a multiobjective optimal fuzzy logic controller (FLC) driven hybrid mass damper (HMD) system for seismically excited torsionally coupled building structures. Floor acceleration and velocity information have been used as feedback to the fuzzy logic controller. A three branch tournament Genetic Algorithm has been used for the multiobjective optimal design of the FLC driven HMD system, where the minimization of the non‐dimensionalized peak displacement, acceleration and rotation of the structure about its vertical axis, have been as the three objective functions. The proposed multiobjective optimal fuzzy logic controller has been verified for an example problem reported in the literature. This HMD system consists of four HMDs arranged in such a way that the system can control the torsional mode of vibration effectively in addition to the flexure modes of vibration. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
8.
Dynamic response behaviour of a simple torsionally coupled system with Multiple-Tuned Mass dampers (MTMDs) is investigated. The system is subjected to lateral excitation that is modelled as a broad-band stationary random process. MTMDs with uniformly distributed frequencies are considered for this purpose and they are arranged in a row covering the width of the system. A parametric study is conducted to investigate the effectiveness of MTMDs on reducing the response of torsionally coupled system. The parameters include the eccentricity of the main system, its uncoupled torsional to lateral frequency ratio and the damping of MTMDs. It is shown that the effectiveness of MTMDs in controlling the lateral response of the torsionally coupled system decreases with the increase in the degree of asymmetry. Further, the effectiveness of MTMDs, designed for an asymmetric system by ignoring the effect of the torsional coupling, is overestimated. © 1997 by John Wiley & Sons, Ltd. 相似文献
9.
A new parameter estimation algorithm is described for identifying the stiffness properties of torsionally coupled shear buildings from their linear response due to ambient excitations or during low-amplitude forced-vibration tests. The algorithm is based on the time-domain equations of motion, and yields estimates of the stiffness properties using a measure of the equilibrium of forces acting on each floor over a time interval. The banded structure of the stiffness matrix — a property intrinsic to torsion-shear buildings — is exploited to decompose the initial inverse problem into several problems of reduced size. This decomposition allows the identification of lateral and torsional stiffnesses of individual stories, independent of the others. The algorithm utilizes vibration data where input excitation is known/measured, which is typical for forced-vibration tests and earthquakes. If the ambient vibrations of the structure are adequately uncorrelated to the (unknown) external forces that induce such vibrations, then the algorithm can also be modified for output-only system identification. The proposed algorithm is verified — and its various attributes are investigated — using simulation data from the ‘Analytical Phase I’ of the IASC (International Association for Structural Control)-ASCE (American Society of Civil Engineers) benchmark studies. The companion article is devoted to the algorithm's application to experimental data, using data from the ‘Experimental Phase’ of the same benchmark studies. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
10.
An approach is formulated for the linear analysis of three-dimensional dynamic soil–structure interaction of asymmetric buildings in the time domain, in order to evaluate the seismic response behaviour of torsionally coupled buildings. The asymmetric building is idealized as a single-storey three-dimensional system resting on different soil conditions. The soil beneath the superstructure is modeled as linear elastic solid elements. The contact surface between foundation mat and solid elements of soil is discretised by linear plane interface elements with zero thickness. An interface element is further developed to function between the rigid foundation and soil. As an example, the response of soil–structure interaction of torsionally coupled system under two simultaneous lateral components of El Centro 1940 earthquake records has been evaluated and the effects of base flexibility on the response behaviour of the system are verified. 相似文献
11.
In order to carry out parametric analysis of eccentric structure–soil interaction system, an analytical model based on branch mode decoupling method is presented in this paper. The solution of system equations is implemented in the frequency domain by assuming that the superstructure maintains classic normal modes. The transfer functions of translational and torsional response are derived later. The influence of eccentricity ratio, torsional to translational frequency ratio, height-to-base ratio and foundation flexibility on the curve and peak value of transfer functions and torsionally coupled degree are analyzed and discussed systematically. Results of analysis indicate that the flexibility of foundation soil can weaken the torsional response of superstructure substantially, and the natural frequencies of interaction system reduce as the flexibility of foundation soil increase. The influence of eccentricity ratio on the peak values of transfer functions varies with the torsional to translational frequency ratio, which can be summarized as the decrease of translational component and the increase of torsional component. The translational displacement of SSI system is larger than that of fixed-base condition, while the deformation amplitude is notably reduced. The torsional response decreases as well. As the height-to-base ratio increase, the varying tendency of response is further enhanced. The torsionally coupled degree of eccentric structure is remarkably affected by the torsional to translational frequency ratio, which is significantly reduced under soft soil condition. 相似文献
12.
The effects of horizontal components of ground motion on the linear response of torsionally stiff and torsionally flexible systems, on soft and firm soil conditions, are examined. A one‐story, two‐way asymmetric structural system is used, subjected to uncorrelated ground motion components along their principal directions. Spectral densities for ground accelerations in firm and soft soils are modeled based on recorded data from large intensity Mexican earthquakes. It is shown that for firm soils, in general, these effects are important in the case of torsionally flexible systems that are stiff under translation, or for torsionally stiff systems that are flexible in translation. The percentage combination rules usually specified in seismic design codes are assessed against the dynamic response. Such combination rules can result in overly conservative design forces or underestimated design forces, particularly for torsionally flexible structures. Given the relative magnitude of the response to each ground motion component, it was found that using different percentage values in the combination rules has no significant effect on improving the estimation of the total response. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
13.
This paper aims to extend the consecutive modal pushover (CMP) procedure for estimating the seismic demands of two-way unsymmetric-plan tall buildings subjected to bi-directional seismic ground motions taking the effects of higher modes and torsion into account. Multi-stage and single-stage pushover analyses are carried out in both X and Y directions. Inelastic seismic responses obtained by multi-stage and single-stage pushover analyses for X and Y directions are combined using the SRSS combination scheme. The final seismic responses are determined by enveloping the combined results of multi-stage and single-stage pushover analyses. To evaluate the accuracy of the proposed procedure, it is applied to two-way unsymmetric-plan tall buildings which include torsionally stiff and torsionally flexible systems. The results derived from the CMP procedure are compared with those from nonlinear response history analysis (NL-RHA), as a benchmark solution. Moreover, the advantages of the proposed procedure are demonstrated by comparing the results derived from the CMP to those from pushover analysis with uniform and fundamental effective mode distributions. The proposed procedure is able to accurately predict amplification or de-amplification of the seismic displacements at the flexible and stiff edges of the two-way unsymmetric-plan tall buildings by considering the effects of higher modes and torsion. The extended CMP procedure can accurately estimate the peak inelastic responses, such as displacements and storey drifts. The CMP procedure features a higher potential in estimating plastic hinge rotations at both flexible and stiff sides of unsymmetric-plan tall buildings under bi-directional seismic excitation when compared to the uniform and fundamental effective mode force distributions. 相似文献
14.
This paper analyzes the soil–structure interaction (SSI) effect on vibration control effectiveness of active tendon systems for an irregular building, modeled as a torsionally coupled (TC) structure, subjected to base excitations such as those induced by earthquakes. An H∞ direct output feedback control algorithm through minimizing the entropy, a performance index measuring the trade-off between H∞ optimality and H2 optimality, is implemented to reduce the seismic responses of TC structures. The control forces are calculated directly from the multiplication of the output measurements by a pre-calculated frequency-independent and time-invariant feedback gain matrix, which is obtained based on a fixed-base model. Numerical simulation results show that the required numbers of sensors, controllers and their installation locations depend highly on the degree of floor eccentricity. For a large two-way eccentric building, a one-way active tendon system placed in one of two frames farthest away from the center of resistance (C.R.) can reduce both translational and torsional responses. The SSI effect is governed by the slenderness ratio of superstructure and by the stiffness ratio of soil to superstructure. When the SSI effect is significant, the proposed control system can still reduce the structural responses, however, with less effectiveness than that of the assumed fixed-base model. Therefore, the TC and SSI effects should be considered in the design of active control devices, especially for high-rise buildings located on soft site. 相似文献
15.
This paper develops an optimized procedure for the design of torsionally unbalanced structures subjected to earthquake loading, considering both the serviceability and the ultimate limit states. An optimal design eccentricity expression, in the form of design charts, and an optimal overstrength factor equation, are proposed. Results show that the recommended design procedure can result in nearly equal performance of both the rigid edge and the flexible edge elements. For a wide combination of primary system parameters, the responses of both edge elements are consistently lower than, or in the neighbourhood of, the response of the corresponding torsionally balanced reference model. The proposed procedure retains simplicity and can be easily implemented (with certain limitations) in design practice. It also has the added advantages of requiring the structure to be analysed only once for each limit state in each principal direction (as opposed to twice, in existing code torsional provisions), and results in a significantly lower overstrength factor, compared with the overstrength factors corresponding to the torsional provisions of seismic codes in the United States and Canada. The proposed procedure is also applicable to torsionally unbalanced structures with and without transverse resisting elements. © 1997 John Wiley & Sons, Ltd. 相似文献
16.
It is shown that the method recommended by the Nuclear Regulatory Commission to be used to combine spectral response in the case of closely spaced modes is unnecessarily conservative for certain systems. Closely spaced modes arise in structures from symmetry and where there is a light appendage with a frequency close to one of the natural frequencies of the structure. In the former case, the closely spaced modes do not involve significant interaction between components of the system and the Nuclear Regulatory Commission Guide is reasonable. The latter case, that is when there are closely spaced modes where interaction of components occurs as in the examples of light appendages and torsionally unbalanced buildings, must be treated by consideration of the interacting components. The approach proposed here is that the modes that are not closely spaced be treated by modal analysis and the closely spaced modes, in the case of two closely spaced modes, be treated as a coupled two-degree-of-freedom system. If this is done, the beat phenomenon, the most important characteristic of the interaction, is evident, as is the associated result that the peak response of the coupled system is developed much later than the peak responses obtained in the individual modes. It is shown that the square root of the sum of the squares procedure underestimates, as expected, the response for undamped and very lightly damped systems, but for damped systems the square root of the sum of the squares method can be extremely conservative. It follows that the other methods specified by the Nuclear Regulatory Commission for closely spaced modes must be even more conservative. 相似文献
17.
A simple and general technique to obtain a six-component earthquake input motion of a rigid foundation using three-linear-components earthquake record is presented. Using the multicomponent input, the maximum structural response to an arbitrarily oriented earthquake is derived. The method is applied to determine the response spectrum for a two-d.o.f. laterally and torsionally coupled linear system. The effects of foundation geometry, structural properties and apparent wave velocity on the structural response are investigated. It is found that increasing the foundation size reduces the peak values of the input motion; this reduction is more pronounced for a square foundation than for a circular one. 相似文献
18.
The paper deals with the topic of analyses performed according to modern code provisions, in particular Eurocode 8 (EC8) rules. Non linear static and non linear dynamic analyses of a plan irregular multi-storey r/c frame building designed according to Eurocode 2 (EC2) and EC8 provisions are carried out.The extension of the N2 method to torsionally flexible structures, as applied in previous papers, does not consider the accidental eccentricity, which is prescribed by EC8 also in the case of non linear static analysis. In this paper, three methods combining the accidental eccentricity prescribed by EC8 to the procedure which extends the N2 method to torsionally flexible structures are proposed and discussed. Each of them provides four modal response spectrum analyses (one for each model, corresponding to each position of centre of mass) and eight non linear static analyses (two signs for four models). NLSA(meth. n.2) seems to be the more reliable method of the three proposed, because it better fits absolute displacements obtained by non linear dynamic analysis.In the paper it is also observed that the value of the behaviour factor assigned by EC8 to torsionally flexible systems seems too conservative. 相似文献
19.
An effective procedure is summarized without derivation for estimating the maximum response of a class of torsionally-coupled, multi-storey buildings due to earthquake ground motion characterized by response spectra. The analysis procedure is shown to be efficient and to provide insight into torsional coupling effects because the maximum response of such a torsionally-coupled, N-storey building in its njth mode of vibration is determined exactly by analysing (i) the response in the jth vibration mode (j = 1,2, N) of the corresponding torsionally-uncoupled, N-storey system; and (ii) the response in the nth vibration mode (n = 1, 2 for a one-way symmetric plan) of an associated torsionally-coupled, one-storey system. It is also demonstrated that an earlier, simpler approach in which the total (considering all vibration modes) response of the building is determined from the total response of the two simpler systems is strictly valid only under restrictive conditions, which are identified, but the simpler approach leads to results that are accurate to a useful degree. 相似文献
20.
Ioannis N. Psycharis 《地震工程与结构动力学》1990,19(4):555-575
The dynamic behaviour of systems consisting of two blocks, one placed on the top of the other, and free to rock without sliding, is examined in this analysis. The equations of motion for each ‘mode’ of vibration are derived and criteria for the initiation of rocking and the transition between modes are given. During vibration, the system continuously changes from one mode to another and this makes the response non-linear. This transition may be accompanied by impact, in which case dissipation of energy occurs, the amount of which depends on the relative velocities and the dimensions of the blocks. Also, redistribution of the kinetic energy of the system in the blocks happens. In most cases, the fractional contribution from the upper block to the system energy increases, which results in a larger and longer response of the top block, compared to the vibration of the lower one. 相似文献