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1.
This paper proposes a method for the estimation of the seismic energy demands of two-way asymmetric-plan buildings under bi-directional
ground excitations. The modal absorbed energies of asymmetric-plan buildings are estimated by using the three-degree-of-freedom
(3DOF) modal systems. The 3DOF modal system represents the two roof translations versus the two base shears and the roof rotation
versus the base torque relationships of each vibration mode of two-way asymmetric-plan buildings. Not only the total absorbed
energy but also the portions of the total absorbed energy contributed from translational and rotational deformations can be
respectively estimated. This study verifies the relationship between the signs of modal eccentricities and the trend of uneven
distribution of modal absorbed energy on floor-plan edges of asymmetric-plan buildings. The accuracy of the proposed method
was verified by analyzing one 3-storey and one 20-storey two-way asymmetric-plan buildings subjected to bi-directional ground
motions. The computational efficiency of the proposed method is confirmed by comparing the computation time with that required
by using the nonlinear response history analysis. 相似文献
2.
David M. Lee 《地震工程与结构动力学》1980,8(4):349-359
This paper examines the effectiveness of a bilinear hysteretic base isolation system in lowering the shear forces and torques generated in a structure by two-way, translatory ground motions. The study is restricted to single-storey, three-dimensional structures having asymmetries in both horizontal directions and being excited by the El Centro (May 1940) earthquake motions. It is shown that with base isolation the structural torques are drastically reduced, even if the structural eccentricity is large. This reduction in structural torque is greatest when the isolation system's centre of stiffness coincides with the structure's centre of mass. The highly dissipative action of the isolation system provides strong modal decoupling which prevents the translational motions from resonantly driving the torsional motions. The maximum base displacements, due to both translation and rotation combined are less than 11 cm, which is well within the limits of currently available isolation system components. The dynamic action of the base isolation system is outlined and currently available isolation system components described. 相似文献
3.
多层钢结构基础隔震性能研究 总被引：1，自引：0，他引：1
本文用算例按基底剪力法,振型反应谱法和时程分析法分析了多层基础隔震钢结构和多层钢筋混凝土结构及其对应的非隔震结构的地震力和层间剪力。 相似文献
4.
The paper presents the first three natural frequencies and the corresponding mode shapes for fixed-base multistorey buildings which can be idealized as an equivalent planar coupled shear wall connected in series to an equivalent frame. The coupled wall is modelled as a continuum of uniform properties and the frame as a uniform shear beam, the connection between the two elements being taken as continuous. Solutions are obtained by treating the structure as a lumped parameter system with twenty equidistant discrete masses having only translational inertia. The relevant flexibility matrix is, however, generated from the exact solution of the governing differential equation for the continuum subjected to point loading. The results are presented for various combinations of the three non-dimensional parameters which are sufficient to describe all the geometric and material properties of the system. The mode shapes are presented in terms of the first three normal modes of a uniform slender cantilever. The non-dimensional base shears required for the response spectrum analysis of buildings of the type under consideration are also given for the three modes and for the various combinations of the three non-dimensional parameters mentioned above. The use of the results is illustrated by an example. 相似文献
5.
This paper examines higher mode effects in systems where the ductile mechanism for seismic design is the base moment‐rotation response. The modal properties of flexural and shear beams with uniform mass and elasticity and with a variable amount of base rotational restraint are derived. As the base fixity is released, the first mode becomes the rigid body rotation of the beam about the base, but the higher modes change much less, particularly for the shear beam model. Most response quantities that are of interest in the seismic design of typical mid‐rise buildings are controlled by the first two lateral modes, except at locations along the height where the second mode contributes little. However, the third and higher lateral modes are more significant for high‐rise buildings. Based on the theory of uniform cantilever shear beams, expressions are developed to avoid the need for a modal analysis to estimate the overturning moment, storey shear, and floor acceleration envelopes. Considering the measured response from the shake table testing of a large‐scale eight‐storey controlled rocking steel braced frame, the proposed expressions are shown to be of similar or better accuracy to a modified modal superposition technique, which combines the higher mode response from an elastic modal analysis with the response associated with achieving the maximum base overturning moment according to an inverted triangular load distribution. Because the proposed method uses only parameters that are available at the initial design stage, avoiding the analysis of a structural model, it is likely to be especially useful for preliminary design. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
6.
A scheme is proposed to calculate the effect of torsion on each lateral load resisting element of asymmetrical buildings in the context of the response spectrum technique. The scheme consists of: (i) Obtain the modal shear and torque on the building by the response spectrum technique, (ii) Compute the total modal shear forces on each frame by resolving the modal shear and torque on the building according to principles of structural mechanics. The shears on each frame due to the lateral load effect and torsional effect are combined algebraically, (iii) Obtain the total shear force on each frame by combining the total modal shears on that frame in a root sum square manner. Since the proper phase relationship between the lateral load effect and torsional effect is accounted for on a modal basis, it is believed that the proposed scheme provides a more realistic load estimate on the frames than the conventional approach. An example of a simplified mono-symmetrical frame structure is chosen to illustrate the accuracy of the proposed scheme, using dynamic time-history analysis as a standard for comparison. 相似文献
7.
An approximation approach of seismic analysis of two‐way asymmetric building systems under bi‐directional seismic ground motions is proposed. The procedures of uncoupled modal response history analysis (UMRHA) are extended to two‐way asymmetric buildings simultaneously excited by two horizontal components of ground motion. Constructing the relationships of two‐way base shears versus two‐way roof translations and base torque versus roof rotation in ADRS format for a two‐way asymmetric building, each modal pushover curve bifurcates into three curves in an inelastic state. A three‐degree‐of‐freedom (3DOF) modal stick is developed to simulate the modal pushover curve with the stated bifurcating characteristic. It requires the calculation of the synthetic earthquake and angle β. It is confirmed that the 3DOF modal stick is consistent with single‐degree‐of‐freedom modal stick in an elastic state. A two‐way asymmetric three‐story building was analyzed by UMRHA procedure incorporating the proposed 3DOF modal sticks. The analytical results are compared with those obtained from nonlinear response history analysis. It is shown that the 3DOF modal sticks are more rational and effective in dealing with the assessment of two‐way asymmetric building systems under two‐directional seismic ground motions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
8.
Farhad Behnamfar Sayed Mehdi Taherian Arash Sahraei 《Bulletin of Earthquake Engineering》2016,14(11):3025-3046
In this study a new method for nonlinear static analysis based on the relative displacements of stories is proposed that is able to be implemented in a single stage analysis and considers the effects of an arbitrary number of higher modes. The method is called the extended drift pushover analysis procedure (EDPA). To define the lateral load pattern, values of the relative displacements of stories are calculated using the elastic modal analysis and the modal combination factors introduced. For determining the combination factors, six different approaches are examined. Buildings evaluated in this study consist of four special steel moment-resisting frames with 10–30 stories. Responses including relative displacements of stories, story shear forces and rotation of plastic hinges in each story are calculated using the proposed approaches in addition to modal pushover analysis and nonlinear dynamic time history analyses. The nonlinear dynamic analysis is implemented using ten consistent earthquake records that have been scaled with regard to ASCE7-10. Distribution of response errors of story shears and plastic hinge rotations show that a major part of error corresponds to the second half of the buildings studied. Thus, the mentioned responses are corrected systematically. The final results of this study show that implementing the EDPA procedure using the third approach of this research is able to effectively overcome the limitations of both the traditional and the modal pushover analyses methods and predict the seismic demands of tall buildings with good accuracy. 相似文献
9.
Lydell Wiebe Constantin Christopoulos Robert Tremblay Martin Leclerc 《地震工程与结构动力学》2013,42(7):1069-1086
This paper presents the results of 56 large‐amplitude shake table tests of a 30% scale eight‐storey controlled rocking steel frame. No significant damage or residual deformations were observed after any of the tests. The frame had four possible configurations on the basis of combinations of two higher mode mitigation mechanisms. The first mitigation mechanism was formed by allowing the upper section of the frame to rock, so as to better control the mid‐height overturning moment. The second mitigation mechanism was formed by replacing the conventional first‐storey brace with a self‐centering energy dissipative (SCED) brace, so as to better control the base shear. The mechanisms had little effect during records where higher mode effects were not apparent, but they substantially reduced the shear and overturning moment envelopes, as well as the peak floor accelerations, during more demanding records. The reduction in storey shears led to similarly reduced brace force demands. Although the peak force demands in the columns were not reduced by as much as the frame overturning moments, using an upper rocking joint allowed the column demands to be estimated without the need to assume a lateral force distribution. The tests demonstrated that multiple force‐limiting mechanisms can be used to provide better control of peak seismic forces without excessive increases in drift demands, thus enabling more reliable capacity design. These results are expected to be widely applicable to structures where the peak seismic forces are significantly influenced by higher mode effects. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
10.
Seismic shear force magnification in RC cantilever structural walls,designed according to Eurocode 8 总被引：3，自引：3，他引：0
Klemen Rejec Tatjana Isaković Matej Fischinger 《Bulletin of Earthquake Engineering》2012,10(2):567-586
The paper contains a discussion of the inelastic dynamic magnification of seismic shear forces in cantilever walls with rectangular
cross-sections. An extensive parametric study was performed in order to determine the reliability of the procedure in Eurocode
8 (EC8). A large number of single cantilever walls which are characteristic for the design practice in Europe and designed
to satisfy all the EC8 requirements were analysed. The results obtained with the (modified) code procedures were compared
with the results of inelastic response history analyses. If properly applied, the EC8 procedure for DCH walls usually yields
good results for the base shears. However, as presently formulated and understood in the EC8, it can yield significantly incorrect
results (overestimations of up to 40%). For this reason three modifications were introduced: (1) Keintzel’s formula, which
is adopted in EC8, should be used in combination with the seismic shears obtained by considering the first mode of the excitation
only; (2) the upper limit of the shear magnification factor should be related to the total shear force; and (3) a variable
shear magnification factor along the height of the wall should be applied. The present procedure in EC8 for DCM structures
(using a constant shear magnification factor of 1.5 for all walls) is non-conservative. For DCM walls it is strongly recommended
that the same procedure as required for DCH walls be used. 相似文献
11.
At the present time, there is a need for a rational approach for the analysis and design of three-dimensional structures subjected to multi-component earthquake motions. In this paper, a general design criterion for multi-component earthquake input is proposed. A new method for three-dimensional dynamic analysis is presented which estimates maximum displacements, forces or stresses for specified points within a structure. For each maximum value calculated, the corresponding critical angle of earthquake input is evaluated. The method is readily incorporated into existing computer programs for earthquake analysis, allowing one computer run to produce mean maximum response values for all possible angles of earthquake input. Combined axial and bending stresses are calculated at the modal level. It is shown that combining modal stresses yields lower estimates than if stresses are evaluated from maximum axial forces and moments. In addition, the method can be used without modifications to perform design checks for arbitrary blast or seawave spectra. 相似文献
12.
Four real buildings with three to six stories, strong irregularities in plan and little engineered earthquake resistance are subjected to inelastic response‐history analyses under 56 bidirectional EC8‐spectra‐compatible motions. The average chord rotation demand at each member end over the 56 response‐history analyses is compared to the chord rotation from elastic static analysis with inverted triangular lateral forces or modal response spectrum analysis. The storey‐average inelastic‐to‐elastic‐chord‐rotation‐ratio was found fairly constant in all stories, except when static elastic analysis is applied to buildings with large higher mode effects. Except for such buildings, static elastic analysis gives more uniform ratios of inelastic chord rotations to elastic ones within and among stories than modal response spectrum analysis, but generally lower than 1.0. With increasing EPA the building‐average inelastic‐to‐elastic‐chord‐rotation‐ratio decreases but scatter in the results increases. Static elastic analysis tends to overestimate the inelastic torsional effects at the flexible or central part of the torsionally flexible buildings and underestimate them at their stiff side. Modal response spectrum analysis tends to overestimate the inelastic torsional effects at the stiff or central part of the torsionally stiff buildings and underestimate them at the flexible side. Overall, for multistorey RC buildings that typically have fundamental periods in the velocity‐sensitive part of the spectrum, elastic modal response spectrum analysis with 5% damping gives on average unbiased and fairly accurate estimates of member inelastic chord rotations. If higher modes are not significant, elastic static analysis in general overestimates inelastic chord rotations of such buildings, even when torsional effects are present. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
13.
A study is made of the dynamic behaviour of multistorey steel rigid-frame buildings with set-back towers. The effects of set-backs upon the building frequencies and mode shapes are examined. Then the effects of set-backs on seismic response are investigated by analysing the response of a series of set-back building frame models to the El Centro ground motion. Finally, the computed responses to the El Centro earthquake are compared with some code provisions dealing with the seismic design of set-back buildings. The conclusions derived from the study include the following:
- 1. The higher modes of vibration of a set-back building can make a very substantial contribution to its total seismic response; this contribution increases with the slenderness of the tower.
- 2. Some of the important response parameters for the tower portion of a set-back building are substantially larger than for a related uniform building.
- 3. For very slender towers, the transition region between the tower and the base may be subjected to very large storey shears.
14.
A new modal pushover analysis procedure (VMPA-A) is developed and implemented in MATLAB code for three-dimensional buildings subjected to bidirectional ground motions. VMPA-A uses stepwise force patterns to represent changes in the dynamic characteristics because of the accumulated structural damages. The hybrid-spectrum concept is introduced to account for the bidirectional ground motion effects. Due to enactments of the equal displacement rule and the secant stiffness-based linearization process, nonlinear analysis is performed for specific displacement targets without stipulation of full modal capacity curves for each mode. Horizontal components of an earthquake record are considered simultaneously, and the consistency between the force and displacement vectors for each mode is provided. These are the main advantages of the proposed procedure against modal pushover analysis (MPA). An existing 21-story reinforced concrete building is analyzed to exemplify VMPA-A. The response parameters such as displacements, story drifts, internal forces, strains, etc. are discussed by comparing the results of VMPA-A with nonlinear time history analyses, which is accepted as the “exact solution”. Though consistent demand estimations are obtained for story drifts, displacements and deformations, some conservative results are obtained for story shears. 相似文献
15.
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
16.
In conventional modal analysis procedures, usually only a few dominant modes are required to describe the dynamic behavior
of multi-degrees-of-freedom buildings. The number of modes needed in the dynamic analysis depends on the higher-mode contribution
to the structural response, which is called the higher-mode effect. The modal analysis approach, however, may not be directly
applied to the dynamic analysis of viscoelastically damped buildings. This is because the dynamic properties of the viscoelastic
dampers depend on their vibration frequency. Therefore, the structural stiffness and damping contributed from those dampers
would be different for each mode. In this study, the higher-mode effect is referred to as the response difference induced
by the frequency-dependent property of viscoelastic dampers at higher modes. Modal analysis procedures for buildings with
viscoelastic dampers distributed proportionally and non-proportionally to the stiffness of the buildings are developed to
consider the higher-mode effect. Numerical studies on shear-type viscoelastically damped building models are conducted to
examine the accuracy of the proposed procedures and to investigate the significance of the higher-mode effect on their seismic
response. Two damper models are used to estimate the peak damper forces in the proposed procedures. Study results reveal that
the higher-mode effect is significant for long-period viscoelastically damped buildings. The higher-mode effect on base shear
is less significant than on story acceleration response. Maximum difference of the seismic response usually occurs at the
top story. Also, the higher-mode effect may not be reduced by decreasing the damping ratio provided by the viscoelastic dampers.
For practical application, it is realized that the linear viscous damping model without considering the higher-mode effect
may predict larger damper forces and hence, is on the conservative side.
Supported by: Science Council, Chinese Taipei, grant no. 88-2625-2-002-006 相似文献
17.
张德文 《地震工程与工程振动》1995,15(4):62-66
本文利用改进Ｇｕｙａｎ减缩解逼近特征系统中的惯性力，然后引入普通模态型减缩法中的模态线性组合表达式。从而建立了一种新的组合型减缩技术。该技术的精度在常规情况下好于普通模态法，同时弥补了新近提出的、完备模态型减缩法不能保持原模型的刚体特性的不足。这样，在结构动力模型的减缩技术方面，本文为工程界提供了更多的选择。 相似文献
18.
The paper deals with the representation of dissipative effects by means of equivalent viscous forces. A brief review of the classical analytical treatment of the subject is first presented devoting particular attention to the topics of hysteretic and modal damping. The problem of forming viscous matrices in the case of systems which are non-homogeneous from the point of view of dissipation is then addressed; soil–structure systems are first considered and some accepted techniques for forming the structure contribution to the viscous matrix are reviewed. A different technique is then proposed which avoids some of the drawbacks of the previously quoted methods. In the final section of the paper it is shown how this technique is easily applicable also in the case of systems having internal concentrated dampers of viscous type, this being a situation which is difficult to tackle with usual criteria. 相似文献
19.
The paper presents a detailed reexamination of the effects of three damping models on the inelastic seismic response of structures with massless degrees of freedom. The models considered correspond to (a) Rayleigh damping based on current properties (tangent stiffness), (b) Rayleigh damping based on initial properties, and (c) modal damping. The results suggest that some nonzero damping forces/moments at massless DOFs obtained in multistory frames for the case of Rayleigh damping with tangent stiffness may be numerical artifacts rather than a deficiency of the damping model. The results also indicate that significant artificial numerical oscillations in the velocities of the secondary components of MDOF structures are introduced when modal damping or mass-proportional damping is used. 相似文献
20.
关于结构振型参与系数和振型贡献的分析 总被引：1，自引：0，他引：1
采用振型分解反应谱法求解多自由度弹性体系的地震反应时,为了在满足所需计算精度的前提下减少工作量,需要对振型数量进行合理的选择,而振型数的确定主要取决于结构各阶振型对总体反应的贡献。通过数学推导,对振型贡献及振型数量的选择问题进行了研究。首先,讨论了振型参与系数的性质,在此基础上给出了能够反映结构振型贡献参数的数学表达式,对这些参数的力学含义进行了解释,并给出了相关证明;其次,对有效质量法、振型位移控制法等基于不同振型贡献标准的确定振型数的方法进行了分析比较,指出了其合理性和不足。本文研究对进一步理解结构振型贡献和振型数的选择问题具有一定的理论意义。 相似文献