摘要:

AbstractIn this paper we extend the Lanczos algorithm for the dynamic analysis of structures7to systems with general matrix coefficients. The equations of dynamic equilibrium are first transformed to a system of first order differential equations. Then the unsymmetric Lanczos method is used to generate two sets of vectors. These vectors are used in a method of weighted residuals to reduce the equations of motion to a small unsymmetric tridiagonal system.The algorithm is further simplified for systems of equations with symmetric matrices. By appropriate choice of the starting vectors we obtain an implementation of the Lanczos method that is remarkably close to that in Reference 7, but generalized to the case with indefinite matrix coefficients. This simplification eliminates one of the sets of vectors generated by the unsymmetric Lanczos method and results in a symmetric tridiagonal, but indefinite, system. We identify the difficulties that may arise when this implementation is applied to problems with symmetric indefinite matrices such as vibration of structures with velocity feedback control forces which lead to symmetric damping matrices.This approach is used to evaluate the vibration response of a damped beam problem and a space mast structure with symmetric damping matrix arising from velocity feedback control forces. In both problems, accurate solutions were obtained with as few as 20 Lanczos vectors.

ISSN:0098-8847    

DOI:10.1002/eqe.4290180802

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe boundary element method is used to obtain dynamic stiffness functions of rigid cylindrical foundations embedded in a uniform or layered viscoelastic half‐space. Dynamic stiffness functions of hemispherical foundations embedded in a uniform half‐space are also computed. The direct integral equation formulation is used in combination with the complete space point load fundamental solution that is integrated numerically along the azimuthal coordinate. The approach is easy to implement because of the simplicity of the fundamental solution. The numerical results obtained by this method for cylindrical and hemispherical foundations are very close to corresponding published results obtained by different procedures. A parametric study shows the important effects of the Poisson's ratio on the dynamic stiffness functions of cylindrical foundations embedded in a uniform viscoelastic half‐space. The effect of the bedrock compliance on the stiffness functions is also shown in the case of cylindrical foundations embedded in a soil layer that rests on a be

ISSN:0098-8847    

DOI:10.1002/eqe.4290180803

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe response spectrum method has been widely used in earthquake engineering design, but cannot be directly applied to non‐linear systems such as the lead‐filled rubber bearing used in base isolation systems. An appraoch to determine the equivalent linearized stiffness and damping coefficient of the lead‐filled rubber bearing by use of the results of shaking table tests is developed. Comparisons of time histories for the equivalent linear systems and the actual model show the method gives accurate maxima for displacement and acceleration and at the appropriate times. It is found that the identified parameters vary with the maximum deformation and the simplified formulae that can optimally describe the variations are derived. Using these formulae, an iterative algorithm using the response spectrum method to calculate the dynamic response of buildings isolated by lead‐filled rubber bearings is also pr

ISSN:0098-8847    

DOI:10.1002/eqe.4290180804

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractBased on the results of an extensive parametric study of elastic and inelastic response of SDOF systems, in which the most important structural parameters were varied and ground motions of very different characteristics were taken into account, simple formulae for determining the seismic demand in SDOF systems with natural periods in the medium‐ and long‐period range are proposed. Seismic demand is expressed in terms of the mean values of maximum relative displacements and maximum input energy. These results can be used to provide rough estimates of structural behaviour when different damage models are applied. As well as this, the proposed formulae can be used to construct design spectra of the Newmark‐Hall

ISSN:0098-8847    

DOI:10.1002/eqe.4290180805

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper presents a centrifuge model that is capable of realistically representing soil‐structure systems subjected to earthquake‐like excitation. The model is validated by performing (i) free field soil tests, (ii) dynamic soil‐structure interaction tests and (iii) a numerical analysis of the experimental results. The free field experiments show that the simulated earthquake, which is generated by the hammer‐exciter plate method, is similar in amplitude and frequency content to a real earthquake. The experiments also demonstrate that a confined soil sample can satisfactorily model a horizontal soil stratum of infinite lateral extent when the containment walls are lined with an absorptive material to attenuate wave reflections that would otherwise occur. Measurements of the acceleration at different locations on the free soil surface indicate that the surface motion is fairly uniform over a relatively large area. This is further confirmed by a comparison made between the measured free and scattered field motions for a surface foundation. Next, a series of soil‐structure interaction tests are performed which examine the dependence of radiation damping on the natural frequencies of the structure relative to the fundamental frequency of the soil stratum. The experimental results are shown to be consistent with established theories. Finally, the experimental results are used to compute the stiffness and damping parameters of a two degree of freedom numerical model of the soil‐structure system. The experimental parameters are shown to be in good agreement with calssical text book formulae. This study demonstrates that the centrifuge model consistently behaves as expected for simple, but realistic, dynamic soil and soil‐structure systems, and can, therefore, be used with confidence to examine more complicated systems that are not yet ful

ISSN:0098-8847    

DOI:10.1002/eqe.4290180806

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractClosure of the gap at the abutment joints of bridges has been the source of extensive damage during the 1971 San Fernando and more recent earthquakes. In this paper a model for the investigation of the effects of this gap closure is presented and analysed. The focus of the model is the representation of the non‐linear response of the bridge abutments, the foundation and the columns. The model is used for the investigation of the response of a short bridge located in Californi

ISSN:0098-8847    

DOI:10.1002/eqe.4290180807

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe concept of reducing vibrations in steady‐state problems by introducing appropriately chosen additional or control forces, which have the same frequency and phase as the original excitation forces, has been the subject of some recent papers. In this paper the normal mode method is used to determine the magnitudes of the control forces. This method is simpler in concept than earlier approaches. It is demonstrated that with a single control force resonant response of multi‐degree‐of‐freedom systems can be reduced substantially, particularly for the fundamental resonance in lightly and moderately damped

ISSN:0098-8847    

DOI:10.1002/eqe.4290180808

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe recorded earthquake response of a base‐isolated building—the Foothill Communities Law and Justice Center in Rancho Cucamonga—shaken by the 1985 Redlands earthquake (ML4–8) is discussed and analysed by employing system identification techniques. The calculated response of one‐dimensional and three‐dimensional linear structural models is fitted to the recorded motions of the superstructure using the ‘modal minimization method’ for structural identification, in order to determine optimal estimates of the parameters of the dominant modes of the building. Simple one‐dimensional analyses are used to identify also the effective values of key parameters (e.g. damping) of the isolation system. Furthermore, the recorded motions obtained from the densely instrumented foundation (i.e. below the isolation bearings) of the structure and from the free‐field station located 330 ft1 ft =0.3048 m; 1 mile=1.609 km.from the building show how the presence of the structure affects the incoming seismic waves. It is observed that the transverse component of motion (i.e. the component which is perpendicular to the long dimension of the plan of the building) is affected by the presence of the structure considerably more than the longitudinal component. Factors contributing to this effect are the extreme length of the structure (414 ft) and the rotational motions of the superstructure caused by the spatial variability of ground motion. It is pointed out that, despite the fact that the shift in the effective frequency of the structure induced by the isolation was very small, the elastomeric bearings were very effective in reducing the accelerations transmitted to the structure. This is attributed to the damping capacity of the isolation. Based on the observed response of the building to this small earthquake it can be stated with confidence that the structure performed accord

ISSN:0098-8847    

DOI:10.1002/eqe.4290180809

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe response of base‐isolated buildings to gusting wind is analysed theoretically based on experimental data obtained in a boundary layer wind tunnel. A comparison is made with the response evaluated using existing codes. A special procedure, similar to that of current codes, for computing the alongwind and torsional responses of base‐isolated buildings is presen

ISSN:0098-8847    

DOI:10.1002/eqe.4290180810

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractA Galerkin Finite Element formulation for the dynamic stability analysis of liquid‐filled shells is given in this paper. The coupling among the axial and circumferential modes is investigated. The dynamic stability characteristics of two liquid‐filled storage tanks subjected to vertical, horizontal and rocking seismic excitations are presented. It is shown that a tall tank tends to buckle at distinct frequencies; and for cos θ‐type ground excitation, cos 2θ, cos 3θ and cos 4θ are the dominant modes of failure. On the other hand, in a broad tank, buckling regions overlap each other. In particular, for cos θ‐type ground excitation, the dominant buckling modes are cos 6θ to cos 9θ, and also cos

ISSN:0098-8847    

DOI:10.1002/eqe.4290180811

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY