Characteristics Of Earthquake Ground Motion In Mountainous Area And Their Impact On Seismic Response Of Frame Structure Supported By Stepped Foundation

The earthquake ground motion in mountainous area is affected by the local site effect significantly, which amplitude, phase and frequency vary because of the local irregular topography and soil condition. It’s worthy of studying on characteristics of earthquake ground motion in mountainous area. Mountain building is supported by the foundations of different level. Considering the local site effect, the difference of ground motions on foundations of different level arises, which may adversely affect the structure. Based on understanding the characteristics of earthquake ground motion in mountainous area, study on seismic performance of structure in mountainous area is provided with important application in engineering when considering the differential characteristics of ground motion.In use of four groups of ground motion recorded by mountainous area arrays at home and abroad, the impact of mountain topography on ground motion is comparatively analyzed through analysis of characteristics of time history amplitude, fourier spectrum, response spectrum and differential characteristics of ground motion. Based on ground motion records from ZG Xishan array, example of frame structure supported by stepped foundation is designed depending on the topography, the impact of ground motion in mountainous area on seismic response of structures is comparatively analyzed under uniform excitation from up foundation or off foundation, and multi-support excitations from both up foundation and off foundation. Based on the finite element analysis model, the impact of horizontal and vertical multi-support excitations on seismic response of frame structure supported by stepped foundation is analyzed in detail.The main conclusions of the thesis are as follows:Based on the analysis of characteristics of ground motion recorded by four mountainous area arrays, find: Difference of ground motion from different stations exists in the local topography of bedrock or Soil. Relatively speaking, the difference of ground motion in soil is greater. The differential motion of acceleration, velocity and displacement exists in adjacent stations from mountainous array. The ground motion input difference should be considered in seismic response analysis of structure in mountainous area.The amplification effect of displacement and shear force is mainly concentrated on the part of structure below the scarp under multi-support excitations compared with uniform excitations when horizontal earthquake acts. The seismic response of the part of structure below the scarp is less securable under uniform excitation, whether the ground motion is from up foundation or off foundation.The amplification effect exists in the moment in columns under multi-support excitations compared with uniform excitation when vertical earthquake acts. The moment in columns near the storey above the scarp(the height direction of structure), the moment and axial force in columns near scarp edge(the horizontal direction of structure) require particular attention. The more storeys of the part of structure below the scarp exist, the more evident the amplification effect is. The vertical earthquake action needs to be considered in seismic analysis of structure. The seismic response of frame structure supported by stepped foundation should not be neglected when vertical earthquake acts.