Structural Response And Damage And Ground Vibration Of Subway Station Under Internal Explosion

Recently, terrorist explosion in subway station happens more frequently than ever all over the world. Subway stations are of great crowd density and enclosure surrounding. Once accidental or terrorist explosion occurs inside them, not only causes casualties and damages to facilities nearby the explosive, but also induce strong vibration and damage of the structural components or even lead to the collapse of these structures due to the blast wave. Shock wave might also spread to the ground surface through the soil, causing vibration of the ground which is also a threat to the safety of persons, buildings and facilities on the ground. In order to improve the safety performance of subway station under internal explosion, in this dissertation, three main problems in research of blast wave propagation and damage mechanism of the structure under blast loading are systematically studied. They are (1) propagation progress and attenuation law of blast wave inside subway station; (2) dynamic response and damage of a subway station structure due to internal explosion; (3) ground vibration induced by internal explosion in subway station. The primary work and achievement are as follows:(1) Propagation law and overpressure load of blast wave inside subway station are studied. The current experiments and simulation research achievement in small regular underground structures may not be suitable for the large complicated underground structures like subway stations. Therefore, a new numerical model building method with bigger grid size based on overpressure calculating precision is established using the finite difference program AUTODYN. The propagation process of blast wave inside a subway station is numerical simulated using Euler method, the propagation and attenuation law of blast wave are investigated, safe distances to avoid human casualties are determined, and effects of height of structure and distances of exit from explosive on propagation of blast wave are analyzed. The results show that the blast wave in the subway station is of a longer propagating duration, a slower attenuation, and larger damaging effects on the structure. Different heights of structures not only affect the attenuation of blast wave, but also cause the difference of waveforms. The venting effect of the exit is related to the distance of the exit from the explosive, and the closer the exit from the explosive is, the more remarkable the venting effect is.(2) Dynamic response and damage of a subway station structure due to internal explosion are studied. Based on the nonlinear dynamic analysis software LS-DYNA, a method for simulating the dynamic response and damage of a subway station structure under internal explosion is established. The responses of the structure due to internal explosions from typical small explosive devices, such as suitcase bombs, are simulated. The dynamic displacement and strain of the typical columns, beams and floors are derived for estimating the safety of the structure. Parametric studies are also carried out to investigate the influences of TNT equivalent charge weight, reinforcement ratio of concrete members and soil-structure dynamic interaction on the dynamic responses of the structural members. The results show that the platform floor is the most seriously damaged member under the internal explosion, while minor damage such as small cracks might occur in the member nearby the explosion; Dynamic response of the structure will get stronger with the increase of the TNT equivalent charge weight, and weaker with the increase of reinforcement ratio; The soil-structure dynamic interaction cannot be considered since it has little effect on the dynamic response of the members near the explosion.(3) Blast resistance performance and optimization design of platform column for subway station are studied. Currently, there is no relative research on the blast resistance of platform column under its special explosion scenario available in the literature. In this dissertation, systematic researches are carried out, regarding to the selection of cross section, axial compression ratio, reinforcement form and ratio of stirrups, to propose optimization design methods for improving the blast resistance performance of typical subway station platform columns. The results show that, under the same explosion scenario and column section area, the circular RC column suffers less blast energy than the square one. And by increasing the stirrups ratio, blast resistance capability of circular column can be more significantly improved than the square one. Therefore, a circular cross section is suggested in blast-resistant design of subway station platform column. Reducing the stirrup spacing could significantly improve the blast resistant capability of the platform column, while increasing the diameter of the stirrups or the ratio of longitudinal reinforcement has little effect. Further, a new stirrup arrangement method for circular RC column is proposed to enhance its blast resistant capability. A safety protection distance can obviously reduce the blast pressure on the platform columns and further increase its blast resistance performance. Thus, a conception of reasonable safety protection distance for typical subway station platform columns is proposed with suggested values.(4) Ground vibration induced by internal explosion in subway station is studied. There is no relative research on stress propagation and ground vibration caused by internal explosion in underground structures available in the literature. A case study of typical subway station in Tianjin is carried out to analysis the responses of surrounding soil induced by internal explosion, including the propagation of shock wave in the soil, characteristics of ground vibration and its attenuation law. For typical subway station in China, parametric studies are carried out to investigate the influences of explosive weight and structure buried depth on ground vibration surrounding the subway station. Further, a series of formulas concerning scaled distance and structure buried depth are given to calculate the main parameters of ground vibration at typical positions surrounding the subway station. The results of the research can be used both to estimate the vibration safety of buildings surrounding the subway station under terrorist bombing attack, and to provide theoretical basis for the determination of structure buried depth in blast-resistant design of subway stations.