Dynamic Response And Damage Mechanism Of Reinforced Concrete Structures Under Crash

In recent years, the traffic accidents and terrorisms that always involve crashes happen much more frequently than ever in the world, and have caused some economic loss and casualties. Crashes in the accidents and terrorisms often involve reinforced concrete (RC) structures. In order to reveal the dynamic response and damage mechanism of RC structures under crash, in this dissertation, a series of systematic studies is conducted based on computational dynamics. They are (1) dynamic response and failure modes of RC columns under crash; (2) damage evaluation and reinforcement of RC columns under impact; (3) changing laws of mechanics parameters in collisions between RC bridge structure and vessel. The primary work and achievement can be summarized as follows:(1) Numerical implementations of impact issues are discussed from the perspective of geometric nonlinearity, contact nonlinearity, and material nonlinearity. And the reliability and precision of LS-DYNA code to solve impact issues are verified through the study of elastic bars impact.(2) Dynamic response and failure modes of RC columns under impact are studied. A three-dimensional discrete model of one RC column, in which the connections of steel bar and concrete are treated as bond slip, is established using LS-DYNA code. And correctness of the bond-slip model is verified through comparing with nodes sharing algorithm and checking system energy relations. The effects of rigid ball's mass and initial velocity, concrete strength, longitudinal and transverse reinforcement ratio on the dynamic response of the RC column are analyzed through collision of a rigid ball with the RC column, and failure mode of the RC column under impact is discussed. The results indicate that: the increasing of rigid ball's mass and initial velocity will exacerbate the dynamic response and damage of the RC column; the lateral displacement of mid RC column can not be remarkably decreased by increasing concrete strength when the strain rate effect of concrete is considered; the increases of longitudinal reinforcement ratio and transverse reinforcement ratio can effectively improve the impact resistance capacity of the RC column; the failure modes of the RC column under impact include global and local failures.(3) Damage evaluation of RC columns under crash is studied. On the basis of the bond-slip model mentioned above, a damage criterion is put forward to determine the damage degree of the RC columns under impact based on the residual axial load-carrying capacity of the RC column. And correlativity between damage degree of the RC column and mass, initial velocity of rigid ball is studied qualitatively. The results indicate that: the damage degree increases faster than the mass and initial velocity of the rigid ball when the mass and initial velocity is in a low level, and the damage degree enhances fastest as the mass and initial velocity increase simultaneously; when the mass and initial velocity of rigid ball reach a certain value, the growth rate of damage degree will be lower than the mass and initial velocity's.(4) Reinforcement and protection of RC columns under crash are studied. Dynamic response and damage of RC columns before and after reinforcement are analyzed, and the protective effects of strengthening with externally bonded steel plate and foamed aluminum are compared. The results show that: the two methods can effectively reduce the mechanical response and damage degree of the RC columns; a steel plate 10mm thick has the same effect in decreasing displacement response as well as the foamed aluminum 40mm thick, while in reducing the damage degree, a steel plate 10mm thick is proved better than the foamed aluminum 40mm thick.(5) Changing laws of mechanics parameters in collisions between RC bridge substructure and vessel are studied. A collision between a 2600 DWT oil tanker and the substructure of one railway RC continuous beam bridge is simulated using LS-DYNA. In the simulation, the dynamic interaction between the soil and piles is considered through contact algorithm and nodes coupling algorithm. The time history of ship collision force, penetration and velocity of the ship for the two different algorithms are presented, and relations of them are given. In addition, energy dissipation in every part, deformation response and stress distribution of the substructure are analyzed. The results indicate that rules of ship-bridge collision given by the two algorithms are in good agreement.(6) Complication process of the material secondary development subroutine for LS-DYNA code is detailed taking bilinear elastic-plastic material with isotropic strengthening for example.