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1.
When the finite element method is used to idealize a structure, its dynamic response can be determined from the governing matrix equation by the normal mode method or by one of the many approximate direct integration methods. In either method the approximate data of the finite element idealization are used, but further assumptions are introduced by the direct integration scheme. It is the purpose of this paper to study these errors for a simple structure. The transient flexural vibrations of a uniform cantilever beam, which is subjected to a transverse force at the free end are determined by the Laplace transform method. Comparable responses are obtained for a finite element idealization of the beam, using the normal mode and Newmark average acceleration methods; the errors associated with the approximate methods are studied. If accuracy has priority and the quantity of data is small, the normal mode method is recommended; however, if the quantity of data is large, the Newmark method is useful. 相似文献
2.
Structural identification of Egnatia Odos bridges based on ambient and earthquake induced vibrations
Evaggelos Ntotsios Christos Karakostas Vasilios Lekidis Panagiotis Panetsos Ioannis Nikolaou Costas Papadimitriou Thomas Salonikos 《Bulletin of Earthquake Engineering》2009,7(2):485-501
The dynamic characteristics of two representative R/C bridges on Egnatia Odos motorway in Greece are estimated based on low
amplitude ambient and earthquake-induced vibrations. The present work outlines the instrumentation details, algorithms for
computing modal characteristics (modal frequencies, damping ratios and modeshapes), modal-based finite element model (FEM)
updating methods for estimating structural parameters, and numerical results for the modal and structural dynamic characteristics
of the two bridges based on ambient and earthquake induced vibrations. Transverse, bending and longitudinal modes are reliably
identified and stiffness-related properties of the piers, deck and elastomeric bearings of the FEMs of the two bridges are
estimated. Results provide qualitative and quantitative information on the dynamic behavior of the bridge systems and their
components under low-amplitude vibrations. Modeling assumptions are discussed based on the differences in the characteristics
identified from ambient and earthquake vibration measurements. The sources of the differences observed between the identified
modal and structural characteristics of the bridges and those predicted by FEMs used for design are investigated and properly
justified. 相似文献
3.
H. Wada 《地震工程与结构动力学》1983,11(1):21-31
An analysis is presented of the transient flexural vibrations of an elastic column supported by an elastic half-space under the condition that an arbitrarily shaped free-field lateral acceleration and displacement are given as inputs. Applying Laplace transformations with respect to time and numerical inverse Laplace transformations, the time histories of the column acceleration at the interface and free end, and the column and half-space displacement distributions are obtained. After the input free-field acceleration terminates, slightly damped and almost harmonically variable acceleration is observed. The acceleration frequency after the disappearance of the input acceleration nearly coincides with the resonant frequency of the system. The slight damping with the first resonant frequency, even if the half-space is soft compared with the column, is characteristic of the transient flexural vibrations of a column supported by a half-space. Such a phenomenon is not typical of the transient longitudinal vibration problem. Therefore, it may be concluded: when buildings and structures are subjected to an earthquake or an explosive force, their flexural vibrations will continue with their first resonant frequencies, even if their foundations are soft. 相似文献
4.
The Fourier p-element method is an improvement to the finite element method, and is particularly suitable for vibration analysis due to the well-behaved Fourier series. In this paper, an iteration procedure is presented for solving the resulting nonlinear eigenvalue problem. Three types of Fourier version shape functions are constructed for analyzing the circular shaft torsional vibration, the plate in-plane vibration and annular plate flexural vibration modes, respectively.The numerical results show that this method can achieve higher accuracy and converge much faster than the FEM based on polynomial interpolation, especially for higher mode analysis. 相似文献
5.
本文所謂架空結構是指搁置在較高的支墩上的連續梁結構,例如高架橋梁或水電站的架空輸水管道等。這類結構在承受震動荷載（例如地震）時,常會引起較大的變形和应力。如支墩較粗矮,則在計算較低的頻率時,其作用可近似的以一彈簧支座代替之,而忽略支墩本身的結構震動影響。這是一個常用的假定,可以使計算工作充分簡化。本文首先對這一情况作了詳盡討論,給出较完整的解答,包括起始條件影響在内,並提出用“載常數”及“形常數”的觀念來進行計算。然后本文給出考虑支墩的震動影響時的精確解答,分別就縱横方向的震動進行討論,並指出近似計算公式和精確公式间的關係,近似公式只能在支墩較剛固和計算较低階的頻率時才適用。文中列出了結構作横向諧和震動時的特別解答,可見其計算工作量將比近似法增加不少。 相似文献
6.
H. Wada 《地震工程与结构动力学》1984,12(2):169-179
Transient flexural vibrations of an elastic column supported by an elastic half-space are investigated analytically under the condition that an arbitrarily shaped free-field lateral acceleration is given as an input. Applying the Timoshenko theory to the column and making use of Laplace transformations with respect to time and numerical inverse Laplace transformations, the time histories of the column free end acceleration are presented. Numerical results obtained from the Timoshenko theory are compared with those of a previous paper1 (applying the Bernoulli-Euler theory to the column), and the effects of column slenderness and foundation stiffness on the transient flexural vibrations of the column are clarified. 相似文献
7.
D. G. Gorman 《地震工程与结构动力学》1983,11(6):843-855
This study sets out to analyse the effect of uniform temperature on the natural frequencies of transverse vibration of uniform polar orthotropic annular plates. The method employed is that of the annular finite element technique whereby the flexural and membrane components of the solution are separated. By close examination of the form of the resulting in-plane stress distribution due to the thermal loading, it has been possible to obtain results for a wide selection of specimens by way of one equation and three graphs. 相似文献
8.
Mihailo D. Trifunac 《地震工程与结构动力学》1972,1(2):133-150
The ambient and forced vibration techniques for testing full-scale structures are critically compared. Both methods, based on small level excitation, may be used to determine many mode shapes and frequencies of vibration and the corresponding damping values, with adequate accuracy for most purposes. The two techniques give mutually consistent results. The mode amplitudes determined by ambient and forced vibration tests show systematic departure for high modes and near the top levels of buildings tested. This phenomenon is attributed to the participation of all mode shapes and is a consequence of excitation by a concentrated force near the top of a building and at a frequency differing by only a few per cent from a natural frequency of vibrations. A new way of showing the effect of unwanted modes on the response near resonance of the mode being sought is developed. It is particularly useful for the analysis of steady, forced vibration tests of structures using eccentric mass vibration generators. 相似文献
9.
The purpose of this study is to investigate the effect of retrofitting dynamic characteristics of a damaged laboratory arch dam model, subsequently repaired with high-strength structural mortar and strengthened with composite carbon fiber reinforced polymer. This study constructed in laboratory conditions is a prototype arch dam–reservoir–foundation model. Five test cases of ambient vibration on the arch dam model illustrate the changes in dynamic characteristics: natural frequency, mode shape, and damping ratio, before and after retrofitting. The ambient vibration tests collected data from the dam body during vibrations by natural excitations which provided small impacts and response signals from sensitivity accelerometers placed at crest points. Enhanced Frequency Domain Decomposition Method in the frequency domain extracts the experimental dynamic characteristics. At the end of the study, experimentally identified dynamic characteristics obtained from all test cases have been compared with each other. Apparently, after the retrofitting, the natural frequencies of the dam body increased considerably, demonstrating that the retrofitting, including repairing and strengthening is very effective on the flashback of initial dynamic characteristics. 相似文献
10.
We analyse the problem of radiation of seismic waves by a vibroseis source when the baseplate is subject to flexure. A theoretical model is proposed to account for baseplate flexure, generalizing the well‐known model of the vibroseis source of Sallas and Weber, which was developed for a rigid plate. Using the model proposed, we analyse the effect of flexure on the properties of seismic waves. We show that the flexure does not contribute to the far‐field and mainly affects the readings of the reference accelerometer that is used to measure the force applied to the ground; these readings generally become dependent on the location of the sensor on the plate. For muddy and sandy soils, the effect of flexure on baseplate‐acceleration measurements is nonetheless pronounced at the high end of the vibroseis frequency band only (～100 Hz), and is negligible at all frequencies for stiffer soils. The corresponding phase lags introduced by the flexural vibrations at high frequencies lead to errors in the traveltime measurements (through the cross‐correlation function) of up to 0.6 ms for muddy soils and less for denser soils. We show the existence of an optimal position of the reference sensor on the baseplate and also propose a general method of eliminating the phase lag due to the baseplate flexure in acceleration measurements. 相似文献
11.
Finite element analyses were used to investigate the behavior of the building vibration induced by high-speed trains moving on bridges. The model includes the bridge, nearby building, soil and train. Finite element results indicate that trainload frequencies are more important than the natural frequencies of bridges and trains for building vibrations. If the building natural frequencies approach to the trainload frequencies, which equal an integer times the train speed over the compartment length, the resonance occurs and the building vibration will be large. Moreover, the vibration shape is similar to the mode shape of the resonance building frequency. To isolate the building vibration induced by moving trains, this paper investigates three common types of foundations, which include the extension of retaining walls, pile foundation and soil improvement around the building. Soil improvement around the building is the best way to reduce the building vibration both in horizontal and vertical directions. 相似文献
12.
This paper reports on a study of active vibration control of functionally graded beams with upper and lower surface-bonded piezoelectric layers. The model is based on higher-order shear deformation theory and implemented using the finite element method (FEM). The proprieties of the functionally graded beam (FGB) are graded along the thickness direction. The piezoelectric actuator provides a damping effect on the FGB by means of a velocity feedback control algorithm. A Matlab program has been developed for the FGB model and compared with ANSYS APDL. Using Newmark’s method numerical solutions are obtained for the dynamic equations of FGB with piezoelectric layers. Numerical results show the effects of the constituent volume fraction and the influence the feedback control gain on the frequency and dynamic response of FGBs. 相似文献
13.
The continuous connection method of analysis is extended to deal with the free vibrations of a coupled shear wall structure. The natural modes and frequencies are determined from the Galerkin technique, and the dynamic response following an imposed lateral displacement is evaluated. A comparison is made between theoretical predictions of natural frequencies and the results from tests on model structures. 相似文献
14.
T. Yokoyama 《地震工程与结构动力学》1991,20(4):355-370
A finite element procedure is developed for analysing the flexural vibrations of a uniform Timoshenko beam-column on a two-parameter elastic foundation. The beam-column is discretized into a number of simple elements with four degrees of freedom each. The governing matrix equation for small-amplitude, free vibrations of the beam-column on the elastic foundation is derived from Hamilton's principle. Several numerical examples are provided to show the effects of axial force, foundation stiffness parameters, partial elastic foundation, shear deformation and rotatory inertia on the natural frequencies of the beam-column. 相似文献
15.
弦支穹顶结构动力反应分析 总被引：1，自引：0，他引：1
以天津开发区商务中心大堂的弦支穹顶为研究对象,分析了弦支穹顶结构体系的自振特性,分别运用随机模拟风振分析方法和时间历程分析方法,对其进行了风振和地震反应分析,得到了结构在动力荷载作用下的响应时程,并对分析结果进行了频谱分析和统计分析。研究发现弦支穹顶结构的自振频率呈密集型分布,且振型复杂;结构的风振响应基本以受迫振动为主,没有出现明显的峰值共振现象;结构的地震响应在前几阶基频处出现了较为明显的峰值共振现象;从振动的幅值角度看,风荷载的动力作用效应相对于地震荷载要显著。 相似文献
16.
17.
This paper gives exact Bernoulli–Euler dynamic flexural member equations for a uniform beam on an elastic foundation. These enable exact results to be obtained when the beam is included in free or sinusoidally forced vibration calculations for a plane or space frame, at any frequency. In addition, information is presented to ensure that no natural frequencies are missed in a free vibration analysis. 相似文献
18.
Lin Xiankun~ Zhang Lingmi~ Guo Qintao~ Zhang Yufeng~ .Institute of Vibration Engineering Nanjing University of Aeronautics Astronautics Nanjing China .College of Mechanical Electrical Engineering China .Jiangsu Transportation Research Institute Nanjing China PhD C idate Professor §Associate Professor *Senior Engineer 《地震工程与工程振动(英文版)》2009,8(3):399-407
The dynamic finite element model(FEM) of a prestressed concrete continuous box-girder bridge,called the Tongyang Canal Bridge,is built and updated based on the results of ambient vibration testing(AVT)using a real-coded accelerating genetic algorithm(RAGA).The objective functions are defined based on natural frequency and modal assurance criterion(MAC) metrics to evaluate the updated FEM.Two objective functions are defined to fully account for the relative errors and standard deviations of the natural fr... 相似文献
19.
The basic natural vibration property of the square-based single layer membranous latticed shell is analyzed using the subspace iteration method. Then, the seismic performances of the structure are studied in detail by the mode-superposition response spectrum method, and the reasonable combination number of vibration modes in seismic analysis by the mode-superposition response spectrum method is investigated. In addition, the formulas of seismic time-history response of a long-span spatial structure are deduced considering geometrical non-linearity, and the corresponding computer program is developed. The results by the response spectrum method and those by the time-history method are, then, compared. The researches show that, the seismic performance of the square-based membranous latticed shell is comparatively well, and the reasonable combination number of vibration modes is 15 in the vertical seismic analysis of this kind of structure by the mode-superposition response spectrum method, whereas, it is 60 in the horizontal seismic analysis. Moreover, the results of the vertical seismic analysis of the structure by the mode-superposition response spectrum method are on the safe side, whereas, in the horizontal seismic analysis of the structure, the results must be checked by the time-history method at the end. All this work will provide theoretical guidance to the actual engineering application of this structure. 相似文献
20.
G. B. Warburton 《地震工程与结构动力学》1982,10(3):381-401
In recent papers the author has shown that when determining optimum parameters for an absorber which minimizes the vibration response of a complex system, the latter may be treated as an equivalent single degree-of-freedom system if its natural frequencies are well separated. Emphasis was on minimizing the displacement response when the excitation was a harmonic force. In the present paper simple expressions for optimum absorber parameters are derived for undamped one degree-of-freedom main systems for harmonic and white noise random excitations with force and frame acceleration as input and minimization of various response parameters. These expressions can be used to obtain optimum parameters for absorbers attached to complex systems provided that optimization is with respect to an absolute, rather than a relative, quantity. The requirement that the natural frequencies should be well separated is investigated numerically for the different cases. The effect of damping in the main system on optimum absorber parameters is investigated also. 相似文献