The Load Distribution And Dynamic Response Of Walls And Columns Of Underground Structure Under Internal Explosion

Recently, more and more underground structures were built, such asunderground market and subway station. Once an explosion occurred inside theunderground structure which is caused by terrorist attacks or accidental factors, andinduced structural damage or even collapse, it will lead to serious casualties and hugeeconomic losses. So, it’s necessary to do further research on the overpressure fielddistribution, structural dynamic response and failure mechanism of the undergroundstructure under internal explosion, in order provide reference for blast resistant designand strengthening of underground buildings.Based on the verification of accuracy of ANASYS/LS-DYNA numericalsimulation method on studying the propagation law of the blast wave in confinedspace, this paper analyzed the overpressure distribution on the structural wall and sidecolumn of the underground structure under internal explosion,and studied thedynamic response and damage mechanisms of the wall and side column byestablishing the explosive-air-structure-soil coupling model with the ANASYS/LS-DYNA software. The primary work and achievements are as follows:(1) A separating model of a typical underground frame structure was establishedin this paper and the blast overpressure distribution characteristics of the closedunderground structure under internal explosion were studied. It is found that blastoverpressure on the inner wall surface distributes unevenly and in the intersection areaof inner wall surfaces the reflection overpressure will be enhanced because of thesuperposition and the convergence of the reflection wave while in certain areasaround the detonation point projection the reflection overpressure distributes moreevenly.(2) In this paper, the effect of the explosive weight and the explosive location onthe blast load distribution on the wall and the column surface and the dynamicresponse of the wall and the column were studied. The research shows with theincrement of the explosive weight, the blast load on the wall or the column surfacewill increase heavily but the blast load distribution characteristics are basically all thesame and the displacement and the curvature will rise gradually. For the effect of thedistance between the explosive location and the wall or the column, there is a conclusion that in a certain range the impulse load on the wall or the column surfacewill be strengthened with the increment of the distance, and the response displacementof the wall or the column members will also increase. As for explosive height, aconclusion can be drawn that the change of the explosive height have a significanteffect on the reflection overpressure peak and just have little effect on the impulse;when the explosive is in the middle area of the wall’s or the column’s height, thedisplacement response of the wall or the column is the largest.(3) In this paper, the effect of the soil thickness and the soil property on the blastload distribution on the wall and the column surface and on dynamic response of thewall and the column is also investigated. It is demonstrated that when the members ofthe underground structure have no cracks and no failure the change of the soilthickness will nearly have no effect on the blast load distribution on the wall or thecolumn surface. In addition, under the same explosive weight, the deformation of theunderground structure with covering soil is just1/10of that of the structure on theground with the same size. It shows that the constraint effect of the soil on thestructure’s displacement response is obvious.And in a certain range increasing soilthickness will effectively reduce the displacement response of the wall or the column.For sand, silt and clay, when the soil is clay, the displacement response is the largestand when the soil is sand, the displacement response is the least, the compressionstrength of the soil have an impact on the structural response.(4) This paper discussed preliminarily the simplified calculation model of theblast load on the wall of the closed structure under internal explosion. Based on theequal time centroid simplified model two simplified ideas for the wall’s internal blastloads were proposed which were called partition and no partition equal time centroidsimplified model. It is indicated that under no partition and partition equal timecentroid simplified blast loads the displacement response of the wall is close to theactual displacement response but there is a need to study the way to determining theparameters of the simplified blast load model.