International Journal of Soil Dynamics and Earthquake Engineering最新文献

The dynamic properties of the pile foundation supporting the Imperial County Services Building in El Centro, California, USA, were determined by forced vibration testing. These test results are described in detail and are used to formulate a mathematical model of the foundation. The model is then employed in a study of the interaction between the foundation and building which occurred during the October 1979 earthquake. Differences between the ground motions recorded at the base of the building during the earthquake and those recorded at a free-field site are investigated. Some correlation is seen when these differences are compared to motions computed by applying the measured building base shear to the mathematical foundation model. The disturbances caused by the building at the free-field site is seen to be small.

Considering the fault as a crack in the infinite elastic space, the field of displacement and stress due to forces acting on the lateral surfaces of the crack are obtained. The use of Fourier and Laplace transform methods yield dual integral equations. The solution to these dual integral equations and the formal expressions for the displacements and stresses in terms of integrals are obtained. The forces acting on the lateral surfaces of the crack are assumed to have the following three forms: (a) compressive stress perpendicular to the surfaces of the crack; (b) shear stress along the dip-direction of the crack; (c) shear stress along the strike-direction of the crack. Numerical results are calculated for various values of frequency and Poisson's ratios.

Large deformation seismic analyses of vertical slopes have been performed by employing both the Drucker-Prager perfectly plastic model and the elliptic cap work-hardening model. A comparative study is made between these models and between the finite element method and the limit analysis method. Development and verification of the ‘pseudo-static’ method of the finite element analysis after the sliding as well as before the sliding of the slopes are also studied. Emphasis is placed here on the effect of large deformation of slopes on the evaluation of the overall slope stability problems. Of particular concern is the comparison of the elastic-plastic responses of slopes with different plasticity models for the entire range of earthquake loading including the post failure behavior after the sliding and collapse.

In almost all of the existing investigations on the earthquake response of buried pipelines, the slip between pipe and surrounding soil was overlooked. It is now known through bench-scale and field experiments that the slip phenomenon plays an important role during and after earthquakes. Numerous analytical modellings of very small vibrational amplitudes of the shear force acting at the soil-pipe interface were reported in the literature (for example, Toki and Takada,¹ Ugai² and Parnes³. However, no serious analytical modelling of large vibrational amplitudes for such system is possible until a good model of slipping is adopted.

This paper addresses the concept of large vibrational amplitudes in dealing with the interaction of imperfectly bonded soil-pipe system during earthquakes. The friction at the interface is assumed to be of Coulomb mechanism by a viscous friction model having a viscous coefficient developed by Miller⁴ and Akiyoshi⁵. Analysis is first made for steady-harmonic earthquakes (= plane P- and S-waves) and the slip displacement is represented in closed form which involves some earthquake parameters, soil and pipes in which the break-loose condition for slip is compared with Ugai's⁶ solution. The frequency response function is investigated for the earthquakes with the flat acceleration spectra, and then used for the formulation of pipe and soil strains subjected to randomly vibrating earthquakes.

In this study the following assumptions are adopted:

• 1.

  (1) Soil is linear, homogeneous and isotropic infinite medium, and pipes are long elastic rods without joints.

• 2.

  (2) Frictional stress distributes uniformly around the pipe, and slip occurs when the boundary shear stress equals the frictional one.

• 3.

  (3) Earthquake plane P- and S-waves are correlated with the same spectral distributions.

Simplified methods to evaluate the effects of saturated sandy soil liquefaction are needed for reasonable earthquake resistant design of structures considering the surrounding soil liquefaction. The authors, Iwasaki et al.,¹ proposed two simplified methods with use of a liquefaction resistance factor F_L and a liquefaction potential index I_L to evaluate the liquefaction potential of saturated sandy soils. Based on the proposed methods, the liquefaction potential can be estimated simply by using the fundamental properties of soils, i.e. N-values of the standard penetration test, unit weights, mean article diameters, and maximum acceleration at ground surface. In this paper, the two simplified methods are firstly introduced, and to prove the effectiveness of the proposed methods the values of both F_L and I_L at 64 liquefied sites and 23 non-liquefied sites during past six earthquakes are calculated according to the simplified methods. Also shaking table tests on soil liquefaction are carried out for the saturated sandy model ground. Furthermore, several application methods using the factor F_L, the excessive pore water pressure induced in the saturated sandy soils and the effects of soil liquefaction on the resistance properties of grounds surrounding structures are described.

In order to mitigate the losses induced by major earthquake, it is important to strengthen vulnerable existing structures. To identify this vulnerability, a probabilistic method is needed in which uncertainties from different sources are incorporated. based on seismic hazard evaluation for a site, a single peak power spectrum is used to represent the intensity and frequency content of the ground motion. Assuming a non-stationary Gaussian model for earthquake time history. Monte-Carlo simulation technique is used to generate a set of time histories. Since the input peaks occur at random time and at different random frequencies, the response of the structural system is also random. A statistical analysis of a suitable response parameter (such as ductility demand or moment demand) is conducted and the Gumble Extreme Value distribution is fitted. The ultimate ductility capacity is assumed to have a probability distribution. The reliability of the structure is evaluated by convolving the demand and capacity distributions. A numerical example is presented for illustration. It is shown that with further modification in the proposed method, one could obtain a reasonable estimation of structural safety based upon which a rational decision for strengthening policy can be made.

Seismic hazard has been evaluated at a number of locations in the northeastern United States using probabilistic methods. The analysis was carried out to examine the effects of significant variations in various seismic parameters, reflecting primarily the uncertainty in our knowledge of tectonic processes, inadequate historical data base, and absence of strong ground motion records. Seismic sources were considered in two ways:

• •

  - Using the tectonic province approach that is consistent with the procedure followed by the US Nuclear Regulatory Commission to evaluate nuclear power plants, and in which earthquakes not related to a particular geologic structure are assumed to be associated with a tectonic province.

• •

  - Using seismic zones that were identified solely from the analysis of patterns of historical seismicity.

The maximum earthquake for each province or zone was assumed to be either (a) the historical maximum intensity or (b) historical maximum intensity plus one unit. In both cases, several distant areas (in which earthquakes of intensity ⩾ VIII (MM) have occurred), were considered additional seismic sources. Several published attenuation relationships were also considered. The effects of uncertainty in activity rates were examined by computing rates for several time intervals.

The uncertainty in attenuation relationships contributed significantly to the variation in seismic hazard estimates in the northeastern United States. For the sites studied, there was less than half order of magnitude increase in seismic hazard when the maximum magnitude earthquake was assumed to be historical maximum plus one unit rather than the historical maximum at lower site intensities.