Cumulative Damage Assessment Of Buildings Under Penetration And Explosion

Damage effects analysis and assessment of buildings subjected to multiple penetrating explosions are important issues to be studied urgently in the field of anti-terrorism attacks and military affairs.For the damage effect analysis of buildings subjected to single penetrating explosion,the common method is to combine the explosion test data analysis and the fine simulation of damage process to find out the corresponding relationship between the damage effect of building components and blast power.This is a complex and time-consuming task,highly dependent on a limited number of professionals.Thus,due to inefficiency,the existing method cannot meet the need for rapid damage assessment of buildings in anti-terrorism and military operations.In addition,for the damage assessment of buildings subjected to multiple penetrating explosions,the current method is to consider the mutual independence of each single attack and to calculate the cumulative damage based on mathematically conditional probability,instead of the real physical characteristics of the cumulative damage of the building.Therefore,there is an urgent need for a fast and effective method to realize the cumulative damage assessment of the building subjected to multiple penetrating explosions.Relevant research results can also be applied to the analysis of explosion accidents in production,construction and anti-explosion design of structures.This paper focuses on the cumulative damage assessment of the typical civil buildings of RC frame structure subjected to multiple penetrating explosions.The research consists of several parts,including the fast prediction of the penetration trajectory in the building,the analysis on the blast characteristic of the penetrating explosion,the cumulative damage features and assessment of the building components and the cumulative penetrating explosion damage assessment of the building structures.Research methods and results are applied in the fast assessment of the typical civil buildings of RC frame structure subjected to multiple penetrating explosions.The main research and its innovative achievements are listed as follows:1.Based on the idea of isolation between the projectile and the target and the assumption that the projectile is rigid,a fast algorithm is proposed and extended to predict penetration trajectory into building structures.Based on the description of the projectile's three-dimensional posture,the cavity expansion analysis is carried out and the multi-layer penetration algorithm and the reinforcement equivalent method for the RC were established respectively for the penetration into the building structure.Finally,the fast prediction algorithm of building penetration's trajectory is developed and verified.The research shows that fast prediction algorithm of the penetration trajectory proposed in this paper can effectively predict the penetration trajectory and the residual velocity of the projectile penetrating into the building structure.Compared with the commercial finite element software,the fast algorithm in this paper can greatly reduce computing time and predict effectively with reasonable accuracy.2.The blast load characteristics of buildings under multiple penetrating explosions are analyzed.Due to the reflection enhancement and pressure relief of implosion load in the buildings,an equivalent model of implosion load with the same peak pressure and the double impulse is proposed.The distribution model of the pressure on the components is established and the uniform distribution equivalent load is calculated based on the principle of equal work done by the explosive load and the equivalent load.3.Taking the RC beam as an example,the flexural resistance function characteristics and the damage mode of the RC components are studied.Based on the quasi-static transverse load test results of the RC beam,the flexural resistance functions of the RC members can be described by a three-stage model.Based on the blast tests and the numerical simulations,the damage characteristics and failure modes of RC beams are studied,and the failure modes of typical components such as the slabs and columns are discussed.The results show that the RC beams are prone to local spall failure under near-explosion,and with the aggravation of damage degree,the RC beams are damaged in breach failure and overall flexural failure.The cracks and slight spalls in the RC beams will turn into heavy spalls and even breaches after the secondary explosion.Besides,if the total explosives are the same,the damage caused by a large equivalent explosion is heavier than the cumulative damage caused by two small equivalent explosions.The failure modes of RC members can be divided into the overall flexural failure,the local breach failure and the coupling failure according to different scaled distances and load spatial distributions.4.The cumulative damage of building components such as the RC beams under explosion was studied.The flexural resistance function model for the RC components under multiple explosions is proposed,and the Pressure-Impulse(P-I)diagram for the cumulative explosion damage assessment of the RC components is established based on equivalent single degree of freedom(SDOF)method.As to the local breach failure of the RC members,the assessment criterion of the cumulative damage is proposed by considering the relative spall thickness of the RC components.A joint assessment criterion for the blast damage is proposed considering the overall and local failure modes of the RC members.Finally,the joint assessment criterions for the cumulative blast damage of the RC beams,plates,columns and other typical building components are established.5.The cumulative damage assessment of the civil building with the typical RC frame structure under multiple penetrating explosions is studied.Based on the characteristics of structural and functional damage of buildings,a target equivalent method of component damage to structural damage is proposed,and then the cumulative damage assessment criterion of the building subjected to the penetrating explosion is established.Based on the fast penetration trajectory prediction algorithm and cumulative damage assessment criterion,the fast cumulative damage assessment algorithm is developed for the building subjected to the multiple penetrating explosions.With the fast algorithm,the cumulative damage assessment for a typical civil building with four-story RC frame structure under multiple penetrating explosions is carried out.The research shows that structural and functional damage assessment criterion can both assess the damage of the building effectively,and the functional damage of the building is more serious than the structural damage.In addition,the anti-blast capacities of the beam and the column which are the important bearing components are strong.Reinforcement on the bottom columns can effectively improve the anti-blast and bearing capacity of the building.Due to the influence of the internal damage of buildings,the overall damage of the building is most serious when detonating the charge on the second layer of a four-story building.When the strike equivalent is the same,the damage of the building caused by single penetrating explosion with large equivalent is more serious than that caused by multiple penetrating explosions with small equivalents.