Analysis On Seismic Performance And Simplified Calculational Method Of Underground Construction

As a resource, underground space has been utilized widely in energy sources, traffic, communication, city construction, and national defending engineering, etc. The traditional concept that "underground structure does not need to undertake seismic design"was changed by the Kobe earthquake in 1995, and the ant-seismic research of underground structure has been gradually developed. As a special kind of underground structure, the seismic design of underground construction is different from others. At present, the ant-seismic research of the underground construction is not paid adequate attention; the study on the seismic performance of it is not enough. There is no calculational method or relevant code of seismic design which can be used in the ant-seismic design of underground construction. It is just against such a background that the topic studied in this essay is presented.Based on the characteristics and earthquake disasters of underground construction, the characteristics of underground construction which are different from that of other underground structure or structure on the earth's surface are presented; A 3-D dynamic finite element model that is applicable to underground construction is established and verified; Taking the 3-D underground construction as research object, the earthquake resistant behavior of underground construction is analyzed in detail by means of the nonlinear FEA software ABAQUS. The differences of seismic responses between the underground construction and ground structure are analyzed; the influence of soil thickness and rock sort on the ant-seismic performance of the underground construction is studied. In the paper, the rule of seismic response of underground construction is summarized and suggestions for ant-seismic design are proposed; based on it, the problem of 3-D finite element analysis simplified into 2-D finite element analysis model is discussed, the calculation results of several simplified calculational model are compared with that of the 3-D finite element model, some shortcomings the simplified calculational model of are expounded. the equivalent master frame-shear wall structure is modified on account of the longitudinal end-restrain of underground construction. Based on the research, conclusions are given as follows:①It is often assumed that earthquake disasters of ground structure is more serious than underground construction. However, for a same structure built on underground and ground, internal forces and peak interstory drift of underground structure is larger than the other. The main cause of it is dynamic soil pressure under earthquake caused by the surrounding rock. So the simple idea of underground structure is safer than ground structure is not appropriate, the design underground structure should pay attention to seismic resistance.②The buried depth for structure has great influence on seismic response of underground construction. With the augment of buried depth, the seismic response of underground construction first increases, than decreases. To a certain range of depth, the seismic response of underground construction increases with the augment of buried depth; however, over certain depth, the influence of buried depth will becomes little, the seismic response even decreases with the augment of buried depth. It can suggest that the buried depth has impact on the earthquake action of underground construction influenced by surrounding rock.③The rock sort directly affects the seismic response of underground construction. The wall rock softer, the weaker the restraint effects to the underground construction, the greater the deformation, the more dangerous the earthquake resistance of underground structures. Furthermore, with the rock changing from hard to soft, the internal force of the structure first increases and then decreases, the design of underground construction should consider that it is not the rock softer, the greater the structure internal force.④When the simplified model of"typical frame structure+ unit thickness sock"is used to simulate underground construction, peak interstory drift derived from the analysis is greater than the 3-Dmodel, and the trend is not same to that of 3-D model; moreover, the internal force of the structure can't envelope the result of the 3-D model, that is, sometimes internal force will be less than that of the 3-D model, the effects may lead to unsafe situations. So the underground construction model based on simplified plane model of linear underground structure such as metro tunnels is unscientific and unsafe.⑤When the simplified model of"typical frame considering the flange of shear wall + thickness sock in the load range of the frame"is used to simulate underground construction, peak interstory drift derived from the analysis is greater than the 3-D model, and the trend can not absolutely reflect that of the 3-D model; the internal force is greater than that of the 3-D model. So if this model is used, the result is safe, but is also conventional and diseconomy.⑥When the simplified model of"equivalent frame-shear wall+ thickness sock in the longitudinal range of the structure"is used to simulate the underground construction, the trend is similar to that of the 3-D model and the peak interstory drift is times to that of the 3-D model; the internal force of the equivalent frame-shear wall can envelope the result of the 3-D model well and the result is acceptable. Especially when the longitudinal end-restrain is considered, the stiffness of soil is modified by the amplification factor n = 1 + B /L, the interstory drift and internal force of the equivalent frame-shear wall can make better approach of the analysis result of the 3-d model. Therefore, using the equivalent frame-shear wall model can achieve perfect results.