International Journal of Soil Dynamics and Earthquake Engineering最新文献

In this paper, the method of Wong and Trifunac¹ for generating artificial strong motion accelerograms has been extended to generate synthetic torsional accelerograms and their response spectra. The torsional component of strong-motion is gaining attention as it is becoming evident that it may contribute significantly to the overall response of structures to earthquake motions². The synthetic translational component of acceleration is first constructed to have a given Fourier amplitude spectrum and a given duration at the site. It utilizes the characterization of strong shaking in terms of (1) earthquake magnitude and epicentral distance, or (2) Modified Mercalli Intensity at the site. The effects of geologic environment which goven the dispersive properties of ground motion are also included. The synthetic torsional accelerogram is then constructed from the translational component.

The use of parametric time series analysis to describe strong motion accelerograms has proven to be an efficient method requiring few modelling parameters. In this study, an ARMA model was used to represent accelerograms which were first processed using a variance-stabilizing transformation. By analyzing a large number of recorded accelerograms in the State of California, relationships were found between ARMA parameters and physical variables making it possible to simulate earthquake ground motions throughout the region. The validity of these results was tested by comparing the accelerograms and response spectra of the initial and simulated records.

This paper, is an extension of our work on peak statistics of single degree of freedom system, and summarizes new results which provide for computation of expected and most probable values of the first largest, second largest, third largest etc. peaks of response of linear, viscously damped $\text{n-}\text{degree}$ of freedom system. Comparisons with exact numerical simulation on a typical structure show good accuracy for short impulsive, intermediate and for long strong earthquake ground shaking.

Tables of horizontal, coupling, rocking, vertical and torsional impedance functions for a rigid massless square foundation resting on two types of layered viscoelastic soil models are presented. The first soil model corresponds to a uniform layer overlying a uniform half-space. The second soil model corresponds to a layer with linearly varying properties overlying a uniform half-space. The numerical values presented cover a wide range of frequencies and include two Poisson's ration combinations, three values for the contrast between layer and half-space and five values for the ratio of layer thickness to foundation width. The tabulated values should be of use in studies of soil-structure interaction and vibrations of machine foundations.

The response of three-dimensional linear elastic foundations of arbitrary shape placed on a homogeneous, isotropic and linear elastic soil medium to dynamic disturbances is numerically obtained. Both external forces and obliquely incident seismic waves of arbitrary time variation are considered. The numerical method employed is a combination of the time domain Boundary Element Method used for the soil medium and the Finite Element Method used for the flexural foundation plate. This method has advantages over frequency domain techniques in that it provides in a natural and direct way the time history of the response and forms the basis for extension to non-linear problems.

Theoretical and Experimental Analyses of a commercial Force Balance Accelerometer are presented. Through detailed analysis of the feedback logic and electrical low pass filters, differential equation of the overall system has been developed. It is found that, for the accelerometer type tested, the representation of the transducer response by means of a single degree of freedom viscously damped system is not adequate.

The fundamental criterion for stability analysis of an embankment dam is the factor of safety against sliding of a part of the dam slopes. Usually, the dam is treated as a safe structure if this factor of safety is greater than unity. In this case the dam body experiences elastic deformations only. But, if the dam is subjected to a strong earthquake motion its deformations far extend the elasticity limit, so permanent displacements take place. In such a case the factor of safety, as a stability criterion, becomes immaterial, and thus the character and magnitude of the permanent displacements become measures for estimating the overall stability of the dam as a structure. It is important too, that engineering judgement should be introduced in assessing the safety of any dam under consideration.

Having in mind all the above assumptions, an analytical procedure for estimation of permanent displacements has been developed, based upon the physical characteristics of the built-in material, as well as the nature of the ground motion and the response of the structure to that motion. Finally, the proposed procedure has been checked on a real case, where the Upper San Fernando Dam, damaged by the February 9, 1971 earthquake was taken as a pilot structure.