The Dynamic Deformation Analysis Of Underground Structures And Its Influence On Seismic Response Of Adjacent Surface Buildings

With the development of modern society, the increasing cost and decreasing availability of surface land often results in the development of new space and transportation infrastructure placed underground.As a prevalent part of the infrastructure of modern cities,underground structures, such as subway transportation system and underground plaza, are used for a wide range of application and becoming an important part of urban lifeline in China. If underground structures were destroyed during the earthquake, they might result in more serious damage than the surface buildings for their characteristics:population concentration in the structures, space limitation, exit blockage and so on; in addition, it will be confronted with complex difficulties for the repairing. The failures of a number of underground structures in recent earthquake suggest that the seismic performance of underground structures is not safety as being expected; therefore, the seismic analysis of underground structures becomes an important research content and attracts much attention of civil engineering and urban disaster prevention and reduction. Generally, Underground transportation system will be throughout the modern cities, and subway stations may be built in commercial or residential areas where surface buildings already exist, or the presence of an underground transportation facility may attract new construction in its vicinity. As a result, the underground station may not only change the original site conditions, but also may have an effect on local ground motions. Clearly, it is necessary to investigate the interaction between underground structures and adjacent ground buildings since seismic design of surface buildings is commonly based on the assumption that there is no cavity in the foundation.Based on the above issues, the research emphasis in this dissertation are the dynamic deformaction of the underground structures and the influence of underground structures on adjacent surface buildings, and the major contents are concluded as follows:(1) The relationship between racking deformation of structure and wave length of input motion is investigated by pseudo-static interaction analysis when underground station is buried in drained and un-drained conditions separately. The principle and the adaptive conditions are described; The FEM models and a number of harmonious sinusoidal waves whose frequencies are calculated by the dimension of the underground structure are used to determine the variation of the racking coefficient with the excited wave length in both drained and un-drained condition; the adaptive issue which assumes that the static method can be used in dynamic analysis is discussed when the condition is changed from drained to un-drained; finally, the effect of two factors which means flexibility ratio and relative stiffness between ground and structure is also analyzed.(2) Seismic analysis of SDOF systems under near-fault ground motion with velocity pulse is investigated, and racking deformations of the underground structure with rectangle section subjected to far-field and near-fault ground motions are contrastively analyzed. Firstly, the near-fault ground motion with velocity pulse are decomposed into pulse-type component and high-frequency component by wavelet analysis method, and the effect of each component on the SDOF system is studied; Then, the racking coefficients of underground structure with different flexibility ratios and section dimensions are extensively calculated when the structures subjected to excitations with and without pulse, and the effect of near-fault ground motion on the underground structure is discussed and concluded; Finally, the influence of the flexibility ratios on the issue is also studied.(3) The simplified model and the principle of the generalized inter-story drift spectrum are introduced briefly, and the influence of high modes on the inter-story drifts and their distribution along the height of structures is analyzed. The range of areas in where the surface structures will be influenced by the subway station is extensively investgated when the station is buried in different types of homogeneous foundations. According to the Code for seismic design of buildings, the foundations where station is buried are assumed to be three types:soft site, medium soft site and stiff site. Simultaneously, the adjacent structures are equivalently simplified as flexural, shear and combined shear-flexural models. The variation tendency of the inter-story drift ratios of structures is investigated in the three foundations with and without subway station; the relationship between the dimension of the station and the position where the surface buildings exist is emphatically analyzed; the range of area in where the dynamic response of surface buildings will be effected by the subway station is studied and concluded; Finally, the influence of the underground structures on the seismic design patameters of ground motions for different site conditions is investigated and concluded statistically.(4) A subway station with two-story-three-span-island is considered to investigate the influence of the underground structure on the adjacent surface buildings, which is focused on relative stiffness, peak acceleration and deformation types of the structures. Firstly, generalized inter-story drift spectrum combined with two FEM models with and without subway station are used to analyze the change of the inter-story drift of the surface buildings because of the existence of a underground station; Then, the influence of two key factors, the fundamental period of the building and the distance between the building and the station, on the IDR distribution along the height of the structures is investigated; Following, the effect of two factors, the relative stiffness and the PGA of the input motion, on the seismic response of adjacent building is summarized and concluded; Finally, the deformation types for the structures with different foundational periods caused by the existence of a station are extensively analyzed.(5) A typical subway tunnel which is buried in the layered soil is selected to analyze the influence on the dynamic response of the surface adjacent structures. Firstly, based on the generalized inter-story drift spectrum, the variation of the response of the surface structures with the distance from the tunnel is investigated when there is a tunnel in the foundation and not; Secondly, as a characteristic of subway tunnel, it is possible that the surface structures exist on the top of the tunnel, therefore, the influence of subway tunnel on the buildings which stand on the top of the tunnel is investigated; Finally, the difference of IDR distribution along the height between when the tunnel exists and not is summarized, and the deformation types of the structures are analyzed.