| Progressive collapse of the structure is due to the failure of the locality,and then this local damage triggeres the transmission of structural breach between components,eventually leading to the collapse of the whole structure or the disproportionate partial structure relatived to the initial failure.The mechanism of steel framed structure resisting progressive collapse included the "beam mechanism" and "catenary mechanism".Between them,the development of the catenary mechanism was conducive to improve the ultimate bearing capacity of the structure through the axial tension in beams.And the performance of beam-column joints as the structural key part directly affected the development of catenary action and the performance of structural collapse resistance.However,due to the fine rotation performance and large stiffness,the structural catenary mechanism of top-seat angle with double web angles connection could be able to develop under large deformation.Based on the pseudo-static collapse resistance test of beam-column substructure with the top-seat angle with double web angles connection,this paper used the finite element analysis software ABAQUS to simulate nonlinear numerical simulation analysis.Simultaneously,the law of development and transformation mechanism of beam mechanism and catenary mechanism in the process of collapse had been reviewed,and the influencing factors of beam-column substructural collapse-resistant performance and the development of resistance mechanism were analyzed.Mainly,the following aspects of research work were carried out:(1)Based on the development of structural internal force and resistance mechanism transformation rules,this test selected a typical two-beam and three-column substructure model,which joint was simplified as hinge joints.And it designed three different span ratio beam-column substructures with the top-seat angle with double web angles connection and test loading device of simulating structural collapse process,in order to explore the collapse response of the structure under the condition of the middle column failure.(2)This paper carried out pseudo-static collapse tests on three different span ratio of beam-column substructures,drawing bearing capacity-load displacement curves,strain-load displacement curves,and beam's deformation curves,and analysing the structural deformation morphology,the failure characteristic,bearing capacity and the development rule of internal force of specimens,especially the resistance mechanism of beam-column substructure.The results showed that the failure characteristics of specimens were basically consistent,presenting as beam-column joint angle is failure because of fracturing,and the development rule of the bearing capacity of the three beam-column substructures with different span ratio was the similar,but the ultimate bearing capacity are typically different,that performance of the equal span substructure was the highest in the same conditions;the internal force of the beam mainly developed from bending moment to axial force.The resistance mechanism was gradually transformed from the beam mechanism to the catenary mechanism,and the catenary action of equal span beam-column substructure was the strongest.Because the least span ratio of substructure node early destroied,the development of beam axial force was smaller,and the catenary mechanism is the weakest.(3)In the light of beam-column substructure,numerical simulation analysis was carried out by considering the response of the material damage fracture.Through the comparison of the numerical analysis results and experimental phenomena,failure characteristics,bearing capacity and loading displacement curve and the development of the internal force,it showed that numerical simulation analysis results were good agreement with the experimental results,which verified the validity of the numerical simulation method.This paper discussed the influence of different parametric variation on ultimate bearing capacity,internal force development and resistance mechanism of beam-column substructure by the numerical simulation analysis,including beam's span-depth ratio,span ratio of double span beam,the thickness of top and seat angle,the thickness of web angle.The results showed that improvement of the beam span-depth ratio and span ratio led to the axial force in beams increase,and the catenary mechanism increased bearing capacity of structure,but the ultimate bearing capacity is reduced;with the top and seat angle thickness increasing,the bearing capacity of beam-column substructure was improved,and the axial force increased gradually,and the catenary mechanism reduced bearing capacity of structure;for the effect of web angle thickness on the bearing capacity,development of the internal force and the resistance mechanism of beam-column substructure was lesser.With the increase of the web angle thickness,the ultimate bearing capacity,axial force in beams slightly improved. |
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