Study On Seismic Performance Of Linear Large Underground Space Structures

In March 2014, The State Council of the People’s Republic of China issued The National New Urbanization Planning (2014-2020) in which cities with the population of more than 10 million in our country are deemed to be megacities. As a result, there are now 6 megacities in China. With the increasingly larger scale, all cities would resort to underground space for the new development direction especially when the ground development becomes narrow. Not only in megacities but also in many medium-sized cities in China, the construction of underground space has been initiated at present.This paper is to study the narrow linear structures underground (for instance, commercial pedestrian streets built under the urban main roads). The vertical-horizontal ratio of these structures is usually larger than 10:1, resulting in a large stiffness difference between the vertical direction and horizontal direction. That means these structures will react very differently to the earthquake in different directions. In addition, when such a linear structure goes through crossroads and if there exists the underground structure under the crossroad in the horizontal direction with slight stiffness, such underground structures will affect the stiffness ratio of the whole linear structure and the seismic response of the whole structure at this time will be different. While constructing the underground structures, most major cities designed the fortification intensity of 7 degrees. However, such important lifeline engineering structures as narrow linear subways, underground common ditch, and underground commercial streets with of civil air defense effects will suffer devastating destruction and damage in front of the severe earthquake, which will adversely affect the normal urban order. Consequently, it is of great necessity to study the internal force and displacement laws of these lifeline engineering structures during the earthquake by comparing the differences of 9 degrees and 7 degrees for fortification intensity and by presenting the security of these structures under the fortification intensity of 9 degrees.Grounded on the above questions, this thesis focuses on three points. First of all, the narrow linear underground structures and the linear structure under the crossroads and local sunk plaza are built by using the finite element software SAP2000 and then their seismic performance analysis is made on the basis of their changes in terms of the stiffness. Secondly, the seismic response spectrum in such four directions as in X axis, in the direction of 45° to X axis, in Y axis, and in the direction between X axis and Y axis is respectively entered according to the change of stiffness by controlling earthquake direction and then the seismic response of the structure is analyzed. Thirdly, the fortification intensity of 7 degrees and 9 degrees are compared in terms of their seismic performance under severe earthquakes despite the actual engineering fortification in this thesis of 7 degrees. Finally, the analysis results are concluded from the above three ideas and hopefully can offer reference or suggestions for the design of such kind of structures in the future.