Damage Effects On Underground Structures Caused By Accidental Internal Explosions

In recent years, a great number of buildings and structures are destroyed by terrorist blast attacks and accidental explosions, which highlights the importance to resist explosion disaster of buildings. Explosion occurred inside buildings is in an enclosed space and the shock wave flow field inside the structure and the damage of the structure caused by shock wave are different from the explosion occurred in open air. The damage effect of inner explosion on structures, the propagation characteristic of shock wave in the enclosed space and distribution of load on the structure and protective technologies of engineering are still worldwide hot issues to be studied. In this thesis, the damage effect of underground structure under inner explosion is studied by means of investigation of the actual explosion disasters, analysis of inner explosion test results and the numerical simulation analysis results. The primary research and results of this paper are as follows:(1) The damage phenomena and damage characteristics of structure in different explosion modes are acquired by analyzing the typical explosion hazards and the filed test results of explosion in a prototype tunnel. The damage mechanism of structure under blast is preliminarily understood. The results show that, when the explosive is close to the structure, the structures mainly have the local damage shown as blasting pit, material cracking, spallation, penetration damage and the progressive collapse of building owing to the damage of support member. The shock wave is the main factor of failure of the structure. The pressure of shock wave of inner explosion is higher than that of explosion in open air and the attenuation of the shock wave of inner explosion is slower than that of explosion in open air. In addition, although the fragments, ground motion, noise, dust, gas and fire from explosion may not cause serious damage of structure, but they can cause casualties and equipment damage.(2) Based on the explosion dynamics and the theory of finite element, the simulation arithmetic of the dynamic response of structure and the calculation method of shock wave flow field are studied. The applicability of similitude law of blast in the finite element method is analyzed and the necessary condition is given. The mesh generation method of FEM simulation of shock wave is discussed.(3) Aimming at the prototype tunnel tested as above, based on the test data, the damage mechanism of tunnel under the inner explosion is studied. the influence of the shape of explosive, the location of explosive and the explosive weight on the distribution of shock wave load in the tunnel are studied by the FEM, and the propagation of shock wave in a tunnel with and without end walls are analyzed. The formula to evaluate the attenuation of peak value of the reflected shock wave load on the inner surface of the tunnel versus the distance from the center of explosion is proposed and it can be widely applied. It can be expressed as: (?)(4) In order to meet the needs of protective design of the traffic shield tunnel to resist explosion disaster. A three dimensional FEM model of shield tunnel under internal explosion loading is proposed, which can simulate the contact effects of segment-segment, segment-bolt and segment-soil. The damage mechanism of shield tunnel under internal explosion loading is studied. The results indicate that segment joint is the frail part of shield tunnel to resist internal explosion loading and blast-resistant characteristics of shield tunnel is inferior to that of integral cast in-situ tunnel. The damage characteristics of shield tunnel under internal explosion are opening of circumferential segment joints, relative sliding of longitudinal segment joints, tensile damage of ring bolts and bending deformation of longitudinal bolts. Enhance of bolt strength and ductility can improve the blast-resistant characteristics of shield tunnel.(5) According to the need of protective design of underground structure or basement of tall building to resist explosion disaster. The propagation of shock wave in building through passage and room opening is studied. The calculation model and the mesh generation are validated by the result of correlative matrix test, then the blast load characteristics inside explosion chamber and the propagation process of air shock wave in the underground building are studied. The influence of the ratio (W/V) of charge weight(W) to chamber volume (V) and the ratio (A/V2/3) of opening area (A) of chamber to the parameters (V2/3)of chamber volume on the air shock wave, reflect wave,duration of shock wave and impulse are analyzed. The formula to evaluate the attenuation of peak pressure of the shock wave leaking from explosion chamber is proposed.