Whole Process Investigation Of Dynamic Characteristic And Response Assessment For Concrete-Filled Steel Tubular Members Subjected To Lateral Impact

Concrete-filled steel tubular(CFST)members are widely utilized as main load-bearing components in large-scale building structures due to their advantages of high strength and favorable ductility.Apart from the conventional static loads,CFST members may also be threatened by lateral dynamic loads caused by accidents such as vehicle collision and explosive blast during the whole service life-cycle.Therefore,it is of great significance to investigate the impact dynamic characteristics of CFST members.Since the local response,overall response and failure response are all important contents for evaluating the impact resistance of CFST members,thus,it is necessary to investigate the dynamic characteristic and the response assessment in the whole process for the improvement of anti-impact design theory of CFST members.In this thesis,the dynamic characteristic and the response assessment of the whole process for CFST members subjected to lateral impact are systematically investigated by means of theoretical analysis,numerical simulation and existing test.The main contents and conclusions are as follows:(1)Based on the results of drop weight impact tests,the energy absorption of CFST members was calculated and analyzed,and then the corresponding relationship between the energy absorption and the failure pattern of CFST members was revealed.It is found that the initial impact energy is mainly transformed into the energy absorption of local damage and overall deformation.In the local response phase,the overall deformation of CFST members is not obvious,but the impact force and inertia force are large,and the impact location area is at a high level of stress,thus,CFST members consume a certain amount of impact energy through causing local damage macroscopically.In the overall response phase,the plastic deformation of CFST members increases significantly,and the impact force presents a relatively stable loading process,thus,the CFST members absorb most of the impact energy by generating plastic hinges in the bending deformation pattern.(2)The efficient finite element(FE)model of CFST members was established and validated,and the improved FE model suitable for the analysis of whole process dynamic characteristics was proposed creatively to realize the simulation solution of inertia force distribution and energy absorption distribution of CFST members,which provided an effective way for the analysis of dynamic characteristics of CFST members in each response phase.Based on the improved FE model,the motion/stress state and the deformation/energy absorption of CFST members were investigated,the distribution characteristics of inertia force and its role in dynamic balance were explored,and the corresponding relationship between the evolution process of energy absorption distribution and the formation process of plastic hinges was clarified,then the key issues involved in the analysis of dynamic characteristics in each response phase were further revealed.(3)In the local response phase,the shear pattern of CFST members was theoretically investigated and its discrimination approach was further proposed.A simplified model of stress distribution in the local response phase was established,and the most unfavorable shear section of CFST members was determined accordingly.On the basis of revealing the distribution and evolution law of inertia force,the dynamic shear internal force was theoretically calculated in combination with the dynamic equilibrium equation,then the shear pattern of CFST members in the local response phase was quantitatively determined by comparing with the static shear resistance.According to the analysis results of the influencing factors for shear pattern,the regression formula of the shear degree coefficient was fitted,and the discrimination approach of the shear pattern in the local response phase was further proposed.(4)In the overall response phase,the bending pattern of CFST members was theoretically investigated and its discrimination approach was further proposed.According to the mechanical characteristics and the dynamic equilibrium equation of CFST members,the dynamic bending internal force was theoretically calculated,and the plastic bending state of CFST members in the overall response phase was quantitatively determined by comparing with the static plastic ultimate moment.On the basis of revealing the energy absorption distribution and its evolution process,a simplified model of energy absorption for CFST members under plastic bending was established,then the quantitative analysis of the bending stress and the plastic development of CFST members was determined accordingly.According to the analysis results of the influencing factors for bending state,the regression formula of the bending dynamic increase coefficient was fitted,and the discrimination approach of the bending pattern in the overall response phase was further proposed.(5)In the failure response phase,the critical cracking of CFST members was theoretically investigated and its assessment model was further proposed.On the basis of analyzing the critical cracking state and its evaluation factors,the assessment curve of critical cracking(i.e.m-v curve)of CFST members based on impact parameters was fitted through numerical simulation.Then the impact energy of critical cracking of CFST members was calculated and the assessment model of critical cracking was established.According to the geometric relationship between impact energy and assessment model,the cracking state of CFST members could be quickly identified.(6)The assessment method of the whole process dynamic response of CFST members subjected to lateral impact was proposed,and the joint assessment of the overall response degree and local response degree of CFST members was realized.The evaluation index formulas of the overall response and the local response of CFST members were established and its evaluation grades were quantified,then the joint assessment model of the whole process dynamic response of CFST members was proposed.According to the positional relationship between the(m,E)combination point of impact condition and the assessment curve and grade division,the rapid assessment of the whole process dynamic response of CFST members could be realized.Finally,the general construction method and general process of the joint assessment model of CFST members were proposed,in order to provide reference for the improvement of the anti-impact design theory of CFST members.