Study On The Input Motion For The Site And Nonlinear Site Response And Seismic Response Of Long-span Structures

The seismic response of long-span structures is a complicated scientific problem and it is related with the input motion, site response and structural seismic response. This thesis focuses on the three key factors. The study is helpful for establishing simple and practical site input motion, site response and structure response methods.This thesis focuses on the problems listed above and the research results are listed as follows.1. Based on geometric affine transformation, an efficient algorithm is proposed that transforms the overlap of the ellipse-polygon to an equivalent circle-polygon overlap situation by an affine transformation. Through this transformation, the original problem is transformed to a finite number of conceptually similar problems, which can be easily solved by single algorithm. This algorithm is programmed into seismic hazard analysis, which provides the input motion for the site or structure.2. For deep soft deposit site, the high frequency composites and peak acceleration values of the site response are underestimated if the traditional equivalent linear method is used.The frequency-dependent equivalent linear method considering the moving average and Parzen spectrum window theory and strain threshold theory is proposed in this thesis. With the comparison to the observed earthquake motions for the two methods,results show that the method proposed in this thesis is more effective than the traditional method in simulating wave propagation in the deep soft site. The method proposed in this thesis can be used to obtain the site response of the deep soft site.3. Based on the method to obtiain the site response for layered half-space under oblique incidence in frequency domain and equivalent linear theory, the formula for obtaining equivalent shear strain under oblique incidence is given and the two-dimensional equivalent linear method is developed in this thesis, which can be used to calculate the nonlinear seismic response of free field in layered half-space due to oblique incidence. The nonlinear seismic analysis for one layered half-space under oblique incidence (SH, SV and P) is performed in this thesis, and the effect of the incident angle on the seismic response is discussed.4. Based on equivalent linear method under oblique incidence and viscous-spring superposition artificial boundary, one method for calculating the seismic response of long-span structures considering the effects of nonlinear site, topography and soil-structure interaction with oblique incidence is established.5. Base on the method proposed above, the seismic response including a five-span continuous beam bridge and soil site is conducted under P and SV wave oblique incidence by using ANSYS software. Considering nonlinear site effect, the seismic response of bridge is analyzed with different incident angles, topographies and soil shear modulus. The effects of these parameters on the seismic response of long-span structures are studied. Also, the seismic response of bridge for considering nonlinear site effect and not considering nonlinear site effect is conducted and the results are analysized.