Advanced Materials Research Vols. 243-249

Abstract: In earthquake engineering, the conventional wave motion analyses usually took the subsoil as only one layered soil, and treated the subsoil by using a single freedom system model. Moreover, these methods were often adopted in time domain. In fact, the subsoil are usually stratified due to its forming in different ages, so there exist multiple interfaces which leads to multiple repeated tracings of reflecting and refracting waves in time domain analysis. To avoid the difficulties, a frequency domain analysis method is carried out for linear soil system in this paper, which allows combining all the upward waves and downward waves to a single upward wave and a single downward wave, respectively, and therefore raises great efficiency. The stochastic response analysis of the displacement of layered soils is then performed. The result indicates that, there exists the essential difference in power spectral density (PSD) between stratified soils and single-layer soil, the former has multiple peak values, while the later has only one peak value, and stratified soils have strong filtering effect in high frequency ranges, which can be considered as a low-pass filter.

Abstract: Based on constitutive model of soil and reinforcement-soil, a numerical analysis program is compiled by finite difference method. Strength and deformation characteristics of double twisted hexagonal wire mesh retaining wall under seismic loading are analyzed by 3D finite difference method. The behaviors such as horizontal displacement, settlement of retaining wall, earth pressure of basement and distribution of lateral earth pressure along wall-back are obtained.

Abstract: The equivalent continuous processing is done to multi-element composite foundation by composite material mechanics method, and the composite foundation is studied as transversely isotropic body, the constitutive relation of equivalent complex is established at first time. On the ABAQUS platform, the three direction seismic responses of multi-element composite foundation are studied by finite-infinite element coupling method. The results shown that: (1) the model of equivalent complex can reflect the working mechanics of the multi-element composite foundation; (2) with the increase of the total stiffness of the multi-element composite foundation, the max absolute values of horizontal accelerations and displacements decrease gradually. (3) With the increase of reinforced depth, the horizontal accelerations in reinforced area became small, but the displacements became big. The results can provide reference to the seismic design of structure.

Abstract: Dynamic equations of pendulums in strong motion instrument are analyzed. The equations imply horizontal recordings may be significantly influenced by ground surface tilt while the effects can be ignored for vertical recordings. The difference causes anomaly of horizontal to vertical Fourier amplitude spectra ratio, which is used to identify affected low frequency range.. The low frequency filter based on spectral ratio was employed to estimate the coseismic ground surface tilts in Wenchuan Ms8.0 earthquake. Results show the ground surface tilts are generally less than 1 degree and mainly happened within 30 kilometers to fault surface rupture traces, while rarely discovered in area outside 100 km and squared horizontal peak accelerations less than 200 cm/s². Comparison of ground surface tilts under spectral ratio being 2 and 4, shows ground surface tilting amplitudes usually increased when spectral ratio is decreased, but residual ground surface tilts have small change.

Abstract: In order to understand fully the effect of strong ground motion containing velocity pulse on constant-ductility long-period inelastic spectra, we synthesize two time histories, not containing velocity pulse, whose elastic spectra are identical to that of original time history containing velocity pulse, and whose peak accelerations are as big as that of the original time history. The reason why we synthesize two time histories for one original time history is to avoid the effect of randomicity in selecting sample. We select two time histories of 1999 CHi-CHi earthquake as original time histories, one of which has two synthesized counterparts. It is found that although the elastic response spectra of original time histories are identical with those of their synthesized counterparts, their constant-ductility long-period inelastic spectra are different. We consider that the difference results from the velocity pulses which exist in the original time histories.

Abstract: The solution method for earthquake responses of non-proportion damping system based on Clough-Penzien three-step non-stationary seismic random model is investigated in this paper. Firstly, the unified motion equation of non-proportion damping system is set up and then decoupled by complex mode method. Secondly, the earthquake responses in time-frequency domain are calculated by taking Clough-Penzien three-step non-stationary seismic random model as excitation, which ground motion parameters consistent with that of design response spectrum in china seismic code, and then the non-stationary time-varying variance of earthquake responses can be obtained, subsequently, the variances of equivalent stationary responses are integraled in ground motion duration. At last, an example of base seismic-isolation system is given to show the application of the proposed method.

Abstract: Dynamic setting analysis of Tianchi Volcano future eruption is discussed by combining the analysis result of focal mechanism with that of structural geology. Analyzing anatectic earthquake focal mechanism shows that subduction of West Pacific Plate to the northeast of China makes the Tianchi Volcano region appear to press west-eastward. And analyzing focal mechanism of near-surface foci earthquake tells us that in the region, direction of the axis of the largest principal compression stress is NEE. The research result of structural geology displays that NWW faults around Tianchi is very active since Epipleistocene. Tianchi Volcano future eruption can be controlled by subduction of West Pacific Plate and strike-slip faulting along the NWW. In the end, the dynamic setting of Tianchi Volcano future eruption is put forward.

Abstract: In order to solve the problem of the analysis of seismic response for nonlinear pile-soil-structure interaction system with uncertain parameters subjected to stochastic external excitation, a simple and practical method was proposed in this paper, and the corresponding plug-in program was developed on the platform of universal software ANSYS. Firstly, the stochastic vibration analysis was converted into the definite harmonic vibration analysis accurately by means of the pseudo-excitation method. Secondly, perturbation theory of small parameter was introduced to consider the uncertain material parameters and direct interpolation equivalent linearization model was used to simulate the nonlinearity of material. Finally, the effects of the variability of shear modulus, damping ratio, density and Poisson’s ratio on the stochastic seismic response of the pile-soil-structure interaction system are studied. The results show that the variability coefficients of the response have the same magnitude as the input material parameters and the influence of the variability of material parameters on the response magnitude can’t be ignored.

Abstract: This paper presents the analysis of the dynamic response of a sedimentary valley subjected to incident plane waves. The sediment-filled valley is composed by a fluid layer over a soft soil deposit whose effect is of importance in the design of long span bridges with high piers. The method of analysis makes use of decomposing the problem into interior and exterior regions. In the exterior region, the scattered wave fields are constructed with two linearly independent sequences of Lamb’s singular solutions which satisfy the traction free conditions at ground surface and radiation conditions at infinity. For the interior regions, the wave fields for the fluid layer and soft soil deposit are expressed in terms of wave functions which satisfy the equation of motion. The continuity conditions at the interface of the media are satisfied in the least square sense. The effects of geometric topography, soil amplification and fluid layer under different types of incident harmonic plane waves are analyzed and discussed in detail.

Abstract: To help understand the ground motions of the topographic site, the workers of Seismic Bureau of Gansu province deployed a temporary array of seismometers around the Wenxian hill and recorded ground motions from Wenchuan aftershocks. Only 11 aftershocks were recorded on all stations across the hill, these data were collected to facilitate studies of site response, wave propagation effect, and correlations of mainshock damage with local site conditions. In this paper, we analyze the weak motion data as well as the strong-motion data, and conduct comparisons of peak ground accelerations, seismic spectra analysis, and spectral ratio analysis. A more complete description of the site’s amplification, its relationship to topography, and its relationship to earthquake source effects are provided. The result shows that the ground motion was consistently amplified at station at or near the top of the hill compared with stations at the base of the hill and the amplifications frequency dependent and has its maximum at the resonant frequency of the site.