International Journal of Soil Dynamics and Earthquake Engineering最新文献

A shell model which takes into account the dynamic interaction terms for the earthquake behaviour of buried pipes is presented. A more realistic ground motion input for seismic waves is chosen in the analysis. Then a parametric study is conducted to investigate the effects of pipe radius, slenderness of the pipe, soil stiffness and wave propagation velocity on the modal amplitudes.

A device and its solid state logic are described which improve the uniformity of the optical density of recorded analog traces on film. An example is presented for the Light Control Module LM-8, designed to work in the SMA-1 strong motion accelerograph. Tests have been performed to determine the overall performance of LM-8. The results are very favorable and show that LM-8 improves significantly the overall quality of strong motion acceleration traces recorded on film.

The prescribed motion to be used as base excitation for shear wave propagation studies in soils is not well defined in the literature. This paper utilizes two methods to investigate the concept of utilizing one-half the rock surface velocity as the incident velocity at a transmitting boundary at the soil base. A range of material properties, thicknesses, and frequencies are used to explore the variation of the ratio: incident velocity to rock surface velocity. Although the ratio varies over a broad range recommendations are made to assist the analyst in selecting a conservative ratio suitable for engineering studies.

A statistical approach to design spectrum compatible generation of seismic motions is presented. This problem is addressed on a probabilistic basis, and an earthquake time history is considered as a realization of a nonstationary stochastic process which possesses an evolutionary power spectrum. Thus, the approach is based on relating the power spectrum of the stochastic seismic motion to the design spectrum. In determining the parameters which define the power spectrum, an approximate expression for the probability density of the response of a lightly damped linear structure to a broadband nonstationary stochastic excitation is used. For exemplification, the Newmark-Blume-Kapur (NBK) spectrum and the Housner (H) spectrum are considered. In this regard, analytical expressions of power spectra of stochastic processes which are statistically compatible with the (NBK) and the (H) spectra are derived. These expressions can prove quite useful not only for simulating acxelerograms, but for conducting, as well, stochastic dynamic analyses of structural systems exposed to seismic loads specified by regulatory agencies.

A boundary method is used to solve numerically the problem of scattering and diffraction of SH-waves by cylindrical canals of arbitrary shape in a homogeneous, linear, elastic, and isotropic half-space. A least-square technique has been employed to solve this problem. Results are obtained using a multiple expansion in terms of Henkel's functions. Displacements and stresses near and in the canal wall have been investigated and a comparison with known exact and approximate solutions for SH-wave motion has been studied. Numerical results for displacement and stress amplitudes for different geometries are presented.

The stress and displacement amplitudes in the canal wall and on nearby ground surface change rapidly from one point to another. The higher excitation frequencies lead to greater complexity of the computed motions. For grazing and nearly grazing incidences, a shadow zone is developed behind the canal.

A simple elastic-plastic constitutive model for cohesionless soils is proposed. The model retains the extreme versatility and accuracy of the simple multi-surface J₂-theory in describing observed shear nonlinear hysteretic behaviour, shear stress-induced anisotropy; and reflects the strong dilatancy dependency on the effective stress ratio. The theory is applicable to general three-dimensional stress-strain conditions, but its parameters can be derived entirely from the results of conventional laboratory soil tests. A number of examples are presented including an analysis of seismically induced liquefaction behind a retaining structure.

A numerical method for transmitting waves out of an artificial boundary is presented. It is applicable to linear two- or three-dimensional wave problems with a time-stepping algorithm and a convex artificial boundry. This numerical scheme, expressable in the form of an extrapolation formula, can be implemented easily in finite elements or finite differences. The values at the artificial boundary nodes are calculated with only interior nodal values from time steps past. Limitations of this method are approximately the same as those of the finite element method. The accuracy is controlled by the number of terms in the extrapolation series and can be further improved by decreasing the size of the time step.

The typical response calculation of a single-degree-of-freedom system uses a recursive algorithm for evaluating the relative displacement and velocity {$\text{x[n + 1],}\text{dot}\text{x}\text{[n + 1]}}$ from {$\text{x[n],}\text{dot}\text{x}\text{[n]}}$ and the acceleration values {a[n], a[n + 1]}. Each time step of the iteration requires eight multiplications and six additions. A new algorithm using the digital impulse invariant and step invariant simulation of a continuous system has been derived which requires only two multiplications and three additions. This amounts to a 75% saving in multiplication time and 50% saving in addition time. The accuracy of the new algorithm is guaranteed by the sampling theorem in digital signal analysis. Calculation of the response spectra using the new algorithm is as accurate as that using the old algorithm.