| Explosion,fire and other situations may cause progressive collapse of structures.Although such disasters and accidents rarely occur,they will cause serious losses once they occur.Therefore,it is an important subject that cannot be ignored to analyze the failure modes and collapse resistance mechanisms of various structures.When the column failure,the remaining structure can resist the continuous spread of progressive collapse by forming a resistance mechanism.On the other hand,the joint is the key component to transfer the load,and the collapse failure of the structure is mainly concentrated at the joint.Therefore,the mechanical properties of joints and the mechanism of structural resistance are the two key points in the analysis of progressive collapse resistance of structures,which are worthy of in-depth study and have great significance for disaster prevention and reduction of structures.In this thesis,beam-column structure with T-stub is taken as the research object,and the elastic-plastic material constitutive law and the initial equivalent plastic strain damage criterion are adopted.Through ABAQUS finite element simulation,the anti progressive collapse performance,failure mode and resistance mechanism under the demolition component method and the direct simulation method are investigated.The main research contents and innovation points are as follows:(1)The collapse resistance of substructure with T-stub under the failure condition of middle column,exterior column and corner column was evaluated,and the spatial effect,namely the influence of out-of-plane beam and column restraint on the collapse mechanism,was analyzed.The load-displacement curve,resistance mechanism and side column displacement of three kinds of beam-column substructures were mainly analyzed.(2)The parameter analysis of substructure with T-stub under the failure condition of corner column was carried out to study the span ratio effect,dynamic effect and loading condition effect,that is,the influence of span ratio on the collapse resistance of beam-column substructure,the influence of structural dynamic response and external load form on the vertical displacement of the failed column.(3)The impact load is applied to the single-story beam-column structure,and the effects of connection mode of minor axis,joint strengthening mode,impact block impulse on the progressive collapse resistance of beam-column substructure with T-stub were studied.By comparing the vertical displacement above the corner column and the internal force of beam section,and other data,the change law is summarized.And compare it with the method of dismantling components to analyze the differences between the method of dismantling components and the direct simulation method.(4)On the basis of single-story beam-column structure,considering the superstructure,the anti collapse performance of multi-story beam-column structure under impact load was investigated,and its parameters were analyzed.The effects of different beam span-depth ratio and impact displacement on the collapse performance of multi-story substructure were studied,and the dynamic response behavior of multi-story substructure impacted by a simplified vehicle model was explored.Systematic analysis and numerical results indicate that: The load borne by the middle column before failure will be transferred to the side column more through the beam connected to the major axis direction of the failed column in the small deformation stage after failure,while the load transfer capacity between the major axis and the minor axis direction in the large deformation stage after failure is similar.Under the condition of exterior column failure,catenary mechanism only occurs in the symmetrical direction.Comparing the three kinds of column failure conditions,corner column failure is the most dangerous,because there is no catenary mechanism in beam members.For three kinds of column failure beam-column structures,the plastic rotation angle limit in Do D specification is relatively conservative.Under the failure condition of corner column,the ultimate bearing capacity of beam-column substructure decreases gradually with the increase of span ratio.At the same displacement,the static bearing capacity is greater than the dynamic bearing capacity;The ultimate bearing capacity and ultimate dynamic displacement obtained by the energy balance method are greater than those obtained by the direct dynamic analysis method.The energy balance method overestimates the bearing capacity and deformation capacity of the structure.When the impact mass block impacts the corner column,and the minor axis is connected with traditional type of T-stub,the vertical displacement above the corner column of the beam-column structure is the smallest.When the initial kinetic energy is the same,small impact momentum(high-speed impact with small mass)can cause the collapse of the structure more;Small momentum can stimulate the resistance provided by the catenary mechanism of the beam connected to the major axis of the corner column,but it will make the flexural mechanism of the two span beam quit work in advance.The strengthening of joints has a certain impact on the progressive collapse resistance of the structure,but its impact is relatively small.The vertical displacement above the corner column of the beam-column substructure will be greatly reduced after considering the influence of the superstructure,mainly because the tension will be generated in the beams of the second and third floors to resist the falling of the joint.As the span-depth ratio of the beam and impact displacement increase,the vertical displacement of the joint gradually increases. |
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