摘要:

AbstractIn order to achieve a low isolation frequency, elastomeric bearings used for base isolation of buildings usually have low shear rigidity which leads to a significant reduction in the buckling load. The effects of compression load on the bearing behaviour are therefore an important consideration. A study of seismic response of base isolated buildings is presented in this paper, fully accounting for theP‐Δ effects of isolation bearings. An analytical procedure is formulated that treats separately the superstructure and the supporting bearings and assembles the governing equations via the interaction forces at the base deck. The resulting equations are then solved step‐by‐step numerically. Numerical results obtained for a base isolated five‐storey shear building show that neglecting theP‐Δ effects can lead to considerable errors in the computed seismic response when the buckling safety factor of bear

ISSN:0098-8847    

DOI:10.1002/eqe.4290180402

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractIn the analysis of structural foundations for seismic loads, it is customary to distinguish two types of soil‐structure interaction effect: kinematic interaction (or wave passage), and inertial interaction. The former refers to the phenomenon of wave scattering, which occurs because the foundation is much stiffer than the surrounding soil and cannot accommodate to its distortions. Inertial interaction, on the other hand, is caused by feedback of kinetic energy of the structure into the soil. This paper is concerned only with the first phenomenon.The rigorous analysis of rigid, embedded foundations subjected to seismic disturbances requires, in general, substantial computational effort. Indeed, a typical analysis would normally require models with finite elements and/or boundary elements. Although such methods may be used to find an accurate solution to the problem of kinematic interaction, their use is not always warranted, given the many uncertainties involved and the multitude of assumptions that must be considered. Hence, approximate solutions are attractive for this problem. One such approximate method is the remarkably simple algorithm proposed by Iguchi.3This paper presents first an appraisal of this method by way of a comparison with accurate numerical solutions for cylindrical foundations; next the algorithm is applied to rectangular (prismatic) foundations. It is found that Iguchi's method gives results that are adequate for engineering purposes, even if not entirely accurat

ISSN:0098-8847    

DOI:10.1002/eqe.4290180403

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractIn an effort to study the dynamic characteristics of an arch dam system from the vibration test results, a systematic method of frequency‐domain system identification is developed. The governing equations for system identification are based on a non‐classical modal superposition method. The non‐classical model is shown to be derivable from a general matrix formulation of the dam system. The conventional classical modal formulation becomes a special case of the general non‐classical formulation. The modal parameters of the non‐classical and the classical formulation are to be identified.The system identification method includes a single‐mode sweep procedure for initial parameter estimation and a progressive multiple‐mode parameter identification scheme that contains an information criterion for the determination of the optimal number of modes to be included in the identification process. The method is applicable to data measured at more than one point on the dam and to data that include both the amplitude response and the phase response.The method is applied to the vibration test data of two dams. Based on the results of these applications, the adequacy of the classical model and the non‐classical model is compared and the effect of the phase data on the parameter determinati

ISSN:0098-8847    

DOI:10.1002/eqe.4290180404

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractIn this paper, a method is presented for forced vibration suppression of multi‐degree‐of‐freedom systems with damping. The technique pursued in this investigation is based on applying control forces at a certain number of the system's degrees of freedom. The problem is organized as an unconstrained, non‐linear optimization formulation so that the peak vibration amplitudes of a certain number of degrees of freedom would be minimized. An efficient mathematical programming algorithm is used to solve this optimization problem numerically. It will be shown that the scheme illustrated in this paper is remarkably effective in reducing the vibration of the system. In particular, the vibration amplitudes at selected degrees of freedom may be diminished substa

ISSN:0098-8847    

DOI:10.1002/eqe.4290180405

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractRotational components of seismic waves have been estimated using the strong motion array in Taiwan, SMART‐1. The inner rings of accelerographs, covering an approximately circular area of 3 km2, permit a decomposition of travelling waves with wavelengths in the range 0.5 to 5.0 km and frequencies from 0.1 to 5 Hz.Rotational components of the strain field, obtained from station pairs and averaged over the array using stacking techniques, were computed for five different earthquakes withMsmagnitude 5.7 to 7.8, and epicentral distances 6 to 84 km. The results indicate peak rotation values about a vertical axis on the order of 4 × 10−5rad at an approximately 2.5 s period. The measured values for pure rotation and rocking are in agreement with the spatial coherency structure observed in these earthquakes. For comparison, significant effects to engineered structures generally appear when curlu>10−4rad. The estimates are important for design of scaled engineered models for soil‐structure interaction exp

ISSN:0098-8847    

DOI:10.1002/eqe.4290180406

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractAn approximate analytical solution is presented for earthquake‐induced hydrodynamic pressures on rigid gravity dams with a finite reservoir and incompressible fluid. Using the Trefftz‐Mikhlin method, the solution is constructed with function expansions of solutions of the problem's governing equation which satisfy boundary conditions at the bottom and free surface. Unknown coefficients of the linear combinations are obtained from a continuous least‐squares treatment of the remaining boundary conditions at the upstream dam face and reservoir wall. Numerical results are presented for different geometries of the dam‐water and wall‐water interfaces. Out‐of‐phase motion at the end of the reservoir is considered. When the upstream dam face and reservoir wall are vertical, the known solution for in‐phase dam and wall moveme

ISSN:0098-8847    

DOI:10.1002/eqe.4290180407

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractBy use of the generalized least‐squares procedure, in conjunction with a finite element approximation in time, a simple three‐time‐level family of time integration schemes is derived. This results in fourth‐order accurate unconditionally stable algorithms and stable eighth‐order accurate non‐dissipative algorithms. Numerical examples show the accuracy of the proposed schemes in comparison with the Fox‐Goodwin formula and Newmark's average accele

ISSN:0098-8847    

DOI:10.1002/eqe.4290180408

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractBase isolation can be used both to protect the structure and simultaneously to reduce the response of internal equipment. The seismic response of a base‐isolated structure has been studied through the shaking table test or numerical calculation before. The object of this paper is to analyse a base‐isolated structure by a different analytical approach—perturbation analysis.Recognizing that the horizontal stiffness of an isolation system is much smaller than that of the superstructure, the mathematical expressions of the modal properties of base‐isolated structures are derived by the perturbation method in terms of the modal properties of the superstructure and used to study the dynamic response of superstructure and attached equipment in the base‐isolated building.This study shows that the first base‐isolated mode not only controls the superstructural response but also dominates the response of high‐frequency attachment. The contribution of higher modes to the response of base‐isolated structures, which is proportional to the horizontal stiffness of isolation system

ISSN:0098-8847    

DOI:10.1002/eqe.4290180409

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractA standard test of the Newmark method in structural dynamics is its application to the determination of the response of a damped or undamped single‐degree‐of‐freedom system to a prescribed initial displacement or velocity. In this paper formulae for the error,Δj, in the response, after applying the Newmark method forjtime‐steps each of duration Δt, are proposed and their acceptable accuracy is dem

ISSN:0098-8847    

DOI:10.1002/eqe.4290180410

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractTensile stresses exceeding the tensile strength of concrete can develop in concrete dams subjected to earthquake ground motion. This study examines the earthquake response of gravity dams including tensile cracking of the concrete. The interaction between the dam and compressible water is included in the analysis using a numerical procedure for computing the non‐linear dynamic response of fluid‐structure systems. The crack band theory is used to model tensile cracking with modifications to allow for the large finite elements necessary for dam analysis. The earthquake response of a typical gravity dam monolith shows that concrete cracking is an important non‐linear phenomenon. Cracking is concentrated near the base of the dam and near the discontinuities in the face slope. The extensive cracking, which develops due to ground motion typical of maximum credible earthquakes, may affect the stability of dams during and after strong earthq

ISSN:0098-8847    

DOI:10.1002/eqe.4290180411

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY