| The horizontal flexural member of structure gradually become the cable to withstand the tension when the vertical load-bearing components of structure were destroyed;The residual structure rely on the torque formed by the tension and deflection to bear the vertical load through the "catenary mechanism" consists of node and beam.The transitional phase of the catenary is the last line to defense the progressive collapse of the structure,and it is also the key link of structural anti-collapse design.In this paper,the beam-column substructure connecting in minor-axis direction is used as the structural model,using the method of reserve load path,the anti-collapse performance based on catenary theory is studied systematically and the finite element analysis is carried out.(1)Through the three specimens with different span ratios studying under monotone static loads,the failure modes,deformation development,and load-displacement curves are obtained,the mechanism of beam pillar structure under large deformation condition is mainly analyzed and compared.The results show that the failure process of beam-column substructure is divided into the following three stages when the middle column is failed: beam mechanism,beam mechanism to the transition form of the catenary mechanism and catenary mechanism;After the failure of the column and the connection of a beam,the bearing capacity of the beam pillar structure is reduced,but by the internal force redistribution and the catenary mechanism of the contribution of resistance,beam pillar structure of the bearing capacity will be further improved,eventually the connection of beam and column is failed due to node damage failure.The beam-column substructure has played a very well catenary effect under largedeformation,in which the short beam catenary effect provides greater resistance than long beams and the catenary mechanism is played well in long–span beam-column substructure.(2)Based on the experimental study,ABAQUS finite element analysis software was used to quasi-static analysis of the beam-column substructure connecting in minor-axis direction,considering the ductile metal fracture and the double nonlinearity of material and deformation.(3)Based on the determination of the finite element model,the influence of the parameters on the anti-collapse performance of the beam-column substructure are analyzed by changing the span ratio of the beam-column substructure,the height of the beam section and the anti-lateral stiffness of the side column.The results show that with the increase of the span ratio,the initial fracture load of and the ultimate failure load are reduced;The initial fracture failure and failure damage occurred on the short beam;The failure load is affected by the short beam length.When the span ratio is less than 1,the length of the short beam varies with the span ratio,and the failure load increases obviously compared with the initial fracture failure load;When the span ratio is greater than 1,the length of the short beam is 1500 mm and the failure load is about 10% higher than the initial fracture failure load;As the span ratio increases,the contribution of the catenary mechanism to the total resistance increases significantly.Increasing the beam stiffness constraint has a great influence on the load-displacement curve of the beam-column structure with large span;Increasing the horizontal constraint stiffness of beam properly is benefited to the catenary mechanism of the beam-column substructure connecting in minor-axis direction;However,if the horizontal stiffness of the beam is too large,it will adversely affect the catenary mechanism of the beam-column substructure connecting in minor-axis direction. |
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