Synergy Effect Study Of Multiple Damage In Beam-column Connections With Enlarged-scallop

Beam-column connections are vulnerable parts of steel structure,so the seismic performance evaluation is essential.After powerful earthquake,large plastic deformation may occur in beam-column connections which have good ductility.However,due to local buckling may occur in the steel beams which are designed base on the strong column-weak beam theory,meanwhile and generally speaking,there are essential welding lines and scallops near the beam end,there are still different extent cracking phenomena even though the steel beam-column connections have good ductility,so that the damage such as ductile cracking and local buckling will be coupled and coordinated.For now,scholars at home and abroad are mostly devoted to one aspect of local buckling or ductile cracking.However,it is clearly not enough to focus on one kind of damage germinating and developing when the synergy of multiple damage exist in beam-column connections.Therefore,it has a significant impact on performance-based seismic design to reveal the damage and failure mechanism of beam-column connections under the synergy effect of multiple damage such as local buckling and ductile cracking.In this thesis,according to the existed damage experiment of steel beam-column connections under cyclic loading,the three-dimensional finite element model is established by ABAQUS finite element software,moreover,the user material subroutine UMAT that consist of the mixed nonlinear hardening constitutive model and the cyclic void growth model(CVGM)is improved.And the simulation process of reflecting ductile cracking is achieved through the adoption of Activated-Deactivated element technology.Based on the simulation and experimental results,the relationships of mechanical behaviors in the damage process are systematically analyzed.The main work and conclusions are as follows:(1)The refined modeling and analyzing method are reflected in the numerical simulation,and the damage process of enlarged-scallop beam-column connections is predicted by adopting the Activated-Deactivated element technology and restart analysis technology.The numerical simulation is validated by experimental results.(2)According to the simulation results,the scientific discriminant methods are adopted to capture the occurrence of ductile cracking and local buckling,the relationships of mechanical behaviors in the damage process are analyzed systematically.The synergy effects of local buckling and ductile cracking are among them as the focus to accurately describe the cumulative damage mechanism of enlarged-scallop beam-column connections under powerful earthquake.(3)The analysis results show that the development of ductile cracking and local buckling relate with the load direction,in particular while it is the state of compression,the coupling of local buckling and ductile cracking may accelerate the development of equivalent plastic strain on strain concentration position of local buckling;Before the local buckling occur,cracking may promote the development of equivalent plastic strain of local buckling position;Excessive cracking will causes concentrated energy of the crack position,so that the development of deformation on local buckling part is restrained.Equivalent plastic strain and stress triaxiality both have contribution to the cracking,and they are divided into primary and secondary,but the primary and secondary status sometimes swap.