Investigation On Anti-collapse Performance Of Steel Frame Beam-column Substructure Considering Surrounding Constraints

The progressive collapse of a building is a phenomenon in which the structure is partially damaged due to accidental load,which then causes the continuous failure of the connected components of the failure failure component,and finally leads to a larger range of collapse failure compared to the initial local failure.Many domestic and foreign scholars have studied the anti-collapse performance of frame structures,but only a few have studied the effect of different failure column positions on the anti-collapse performance ability of steel frames.The different position of failure column will lead to the different boundary conditions of beam-column substructure,which inevitably affects its anti-collapse performance.Therefore,it is necessary to carry out further in-depth research on it,so as to provide reference for the revision of structural collapse resistance design code and practical application in engineering.In order to study the influence of different peripheral constraints on the anti-collapse ability of the beam-column substructures,I select two kinds of beam-column substructures with different surrounding constraints to carry out the quasi-static tests under the failure of the middle column.The one is the fully constrained specimens with the failure column located in the middle of the structure.The other one is partially constrained specimens with the failure of the secondary side column.The results show that the form of surrounding constraints affects the deformation bearing capacity of the substructures and the rotational capacity of the joints.The resistance development of the two-span three-column substructure of composite beam goes through three stages: beam bending mechanism stage,beam mechanism to catenary mechanism transformation stage,catenary mechanism.Due to the lack of complete constraint,the catenary effect of some substructures can not be fully developed,which contributes only 15% mechanism resistance.This paper uses the finite element analysis software ABAQUS to establish the numerical analysis models of the fully constrained substructure and the partially constrained substructure.Finally,I have comparative analyzed with the test in load-displacement curve,failure mode,internal force development and mechanism resistance.The results show that the finite element numerical model has high accuracy which can accurately simulates the whole process of anti-collapse of beam-column substructure.The research content of this paper provides a theoretical basis for the parameter analysis of anti-collapse of beam-column substructure by finite element numerical analysis model.The change parameter analysis of the beam-column structure is carried out.First,take the remaining substructure under the failure of the secondary side column as the research object.The research shows that the value of n should be close to 1.5,which can ensure the maximum performance of the catenary mechanism inside the sub-structure.Secondly,based on the investigation of the collapse resistance capacity of the remaining substructures under the failure of the center column.The results show that the internal force of the composite beam on the rigidity side is not much different,and the internal force of the variable lateral rigidity side composite beam increases with the gradual increase of the lateral rigidity.With the gradual increase of the lateral stiffness of the beam ends on both sides,the catenary mechanism resistance of the substructure gradually increases,and the overall bearing capacity of the substructure gradually increases.Thirdly,the size of the side column of the sub-structure is used as the change parameter.The results show that too small size of side pillar is easy to cause the bending failure of column,which will reduce the ultimate bearing capacity of substructure in the later period.When the size of the side pillar is too large,the side pillar acts as a solid connection to the end of the beam,and the bending mechanism of the beam plays a limited role,so its total resistance is also limited.In other words,a substructure with a beam-column rigidity ratio of 0.6-1 is beneficial to improve the anti-collapse bearing capacity of the substructure as a whole.Finally,the influence of the axial compression ratio on the side column on the collapse resistance of the substructure was explored.The results show that the axial compression ratio has little influence on the collapse resistance of the substructure,and the value of the axial compression ratio is 0.3.