| With the development of transportation and architectural structure,the burden of road is growing. For the reason of heavy traffic, accidental event and terrorist attack,the case that vehicle hits the surrounding structure occurs frequently and the risk of surrounding structure collapsed under the impact of vehicle continuous improve. As the process of vehicle hits structure involves contact,dynamic,the failure and fracture of material and so on.The accurate modeling analysis need precise structure and vehicle model and cost large number of analytical time, which lead numerical analysis not widely used in the engineering design.Therefore, three aspects numerical researches of reinforced concrete frame under the impact of vehicle are carried out based on the finite element software LS-DYNA.(1) The sensitivity identification of the key parameters which influence the impact force and the structural dynamic responses is analysized.These factors include the velocity, mass and shape of the impactor,the longitudinal and transverse reinforcement ratios of the column, the strength of concrete and the strain rate of materiald. And based on this,the simplified impact time history curve of reinforced concrete column impacted by rigid body is advanced. Three typical damage modes of the column subjected to impact loading are found from the numerical analysis, including the local damage mode, the global bending failure mode and the local shear failure mode. The factors which influence the impact loading can be classified into three types, i.e. the impactor factor, the stiffness-related factor and the strength-related factor. The different effects of these factors on the peak load, average load and duration of the impact action are discussed which will provide a valuable reference to establish the simplified impact loading model for the collapse analysis of building structures subjected to impact action.(2)In order to guarantee the accuracy and improve the computational efficiency of numerical analysis on the progressive collapse of the RC frames under impact loading, detailed and multi-scale finite element model are established using the finite element software LS-DYNA. The structural progressive collapse response of a RC frame subjected to impact loading is analyzed using the alternative path(AP) analysis and the impact analysis respectively. The results show that the structural dynamic response is underestimated and the wrong collapse mode is obtained via the AP method in which the impact loading and its consequences, i.e. the initial damage, displacement and velocity of the structural members adjacent to the impacted column, are neglected. On the other hand, the dynamic response and the damage mode of the RC frame can be accurately simulated via the multi-scale finite element model with high computational efficiency. The computation time when using the multi-scale model is only about one third of that by using the detailed model which is suitable for the impact analysis for the entire structural systems.(3) Based on the simplified vehicle model consisted of mass-spring system advanced by AL-THAIRY, a computational formula to calculate the relationship of force and deformation of the spring when vehicle impacts a column in oblique direction is advanced. The rationality of the formula is verified by this way that rigid column, reinforce concrete column and reinforce concrete frame are impacted by vehicle. And based on this model,a simplified impact force time history curve of reinforced concrete column impacted by vehicle is advanced. The results show that the impact force have four stages: elastic collision stage, oscillating stage, steady stage and declined stage in which the last three stages are similar to the simplified impact force time history curve of reinforced concrete column impacted by rigid body. Therefore the the simplified impact force of a column impacted by vehicle can be divided into the elastic impacr force and rigid impact force of a column impacted by a rigid body. |
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