Study On Characteristic Method For Site Nonlinear Seismic Response And The Property Of The Silt Soil

Seismic response analysis is one of the core issues of the Earthquake Engineering Research. The characteristic differential method is a nonlinear integral method in time-domain. This method can simulate the actual process of the wave propagation, and taking the dynamic nonlinear characteristics of soil into account. The accuracy of characteristic method can meet the practical requirements, it takes less time and memory than the finite element method, and it is more efficient. So the characteristic line differential method is a more potential method in Seismic response analysis.To take the dynamic nonlinear characteristics of soil into account, we explored the processing methods of the data of resonant column tests. We combined the linear and nonlinear fitting method, and applied the method to the research of the silt soil in Jiaozhou bay. The results show that:1. Compared with the recommended values of doctor YuanXiaoming and seismic safety evaluation code (1994), the Gd/Gdmax～yd curve drops more slowly. This indicates that the modulus of the soils in Jiaozhou bay changes little. These results are more closed to the results of Rune Dyvik and USGS2. Compared with the recommended values of doctor YuanXiaoming and seismic safety evaluation code (1994), the damping curve λd～γd increases also slowly.3. The characteristics of the modulus and damping of the soils in Jiaozhou bay may be affected by the dispersion degree of soil particles, the content of the clay minerals and the degree of the saturation,We computed a site which is composed by the silt by the method of characteristic differential. The results show that:the response spectrum characteristic period of this paper is about 1.3seconds, but the value of the94’s code is apparently larger, about1.8seconds. And the peak value of the response spectrum of the both is close. When we amplified the input to3times of the original, the nonlinear response is visible. Although all of the characteristic period is2.5seconds, the peak value of the response spectrum is different. The peak value of the code is much smaller than the value of this paper. Thus when we conduct a real project, we should do the real test to all the silt sites, then get the real nonlinear parameters of the corresponding silt.To make the results of the characteristic line differential method close to real, we changed the rigid boundary to the transmitting boundary. Thus the surface time history can fall off rapidly. To verify the correction of the transmitting boundary, we presume a single elastic soil layer and calculate the surface pulse wave under the influence of the pulse input. We compared the surface pulse with the theoretical solution, found that:the computed pulse wave conform the theoretical solution well. We changed the Ramberg-Osgood into the parabolic constitutive model. This can make the method combine the damping of resonant column tests.In order to conform the boundary and the constitutive model, we set the real rock record of KiK-net as the input, compared the computed surface time history with the real record history. Made cross-correlation analysis of the found that:1. The sum of the products of the computed time history with the real record history is above zero. This show that the phases are related.2. When the time history is short than30s, the correlation coefficient is above0.35, the computed history and the record are real correlated; When the time history is short than23.5s, the correlation coefficient is above0.5, the computed history and the record are significant correlated; When the time history is20s, the correlation coefficient is0.76, the computed history and the record are highly correlated.In the main energy range, the correlation coefficient is above0.5. This showed that the reaction of the surface can replace the real record on surface. This proved that the modified method is credible.At last, we applied the modified method into the seismic response analysis of the site of Yuxi. We compared the Fourier amplitude spectrum to get the peak magnification times of the velocity and the acceleration. We compared the response spectrum to get the magnification times of the peak value of the response spectrum. We analyzed the magnification of the velocity, acceleration and the peak value of the response spectrum, found that:the magnification times of the velocity becomes larger from west to east; the magnification times of the acceleration and the peak value of the response spectrum becomes litter from middle to two sides.