Study Of Ultimate Bearing Capacity And Failure Modes Of Symmetric And Asymmetric Self-resetting SMA Connections

Based on the "three-level,two-stage" seismic design method,the structure can meet the requirements of bearing capacity,normal use and safety.However,the structure may appear large residual deformation under rare earthquake.When major load-bearing components of the structure,such as beam and column joints,undergo irreparable plastic deformation,residual deformation will gradually accumulate in the structure.Some scholars have shown that when the residual displacement Angle of the structure exceeds 0.5%,it is more economical to demolish and rebuild the building than to repair it.SMA has the characteristics of super elasticity and shape memory effect,which can make the building structure realize self-reset and energy dissipation capacity in the earthquake,and has a good effect of energy dissipation and shock absorption.In steel frame structures,the seismic performance and self-resetting ability of steel frame structures can be effectively improved by using self-resetting beam-column joints and self-resetting supports.Therefore,according to the characteristics of SMA,a beam-column joint based on asymmetric self-resetting SMA connection is proposed in this paper,and combined with the brace based on self-resetting SMA connection proposed earlier,in order to further improve the seismic performance of steel frame structures.Based on this,this paper studies the ultimate bearing capacity,energy dissipation capacity and failure mode of the two connections respectively.The main research work is as follows:(1)Get familiar with the superelasticity and shape memory characteristics of SMA wire through literature.The characteristics of symmetric connection and asymmetric connection proposed by various scholars are studied,and the measures to avoid joint failure of symmetric connection and asymmetric connection in the current beam-column joints are sorted out.The problems existing in the current beam-column joints are proposed based on the above literature,and the technical roadmap is drawn.(2)Design an asymmetric self-resetting SMA connection and study its mechanical properties by taking advantage of the constant tension characteristic of SMA wires.The finite element method was used to fit the test curve and failure mode of the bolted joint of the end plate of the steel frame,and the accurate boundary conditions were obtained.Eight bundles of SMA wires were added to the beam-column joint with reaming bolts to verify the mechanical properties of SMA in the beam-column joint.(3)Limit analysis was carried out for asymmetric self-resetting SMA connections.Considering the influence of cross-sectional area of SMA wire,thickness of end plate and strength grade of sliding screw on the ultimate bearing capacity of the connection,three failure modes of SMA wire breaking,steel plate failure deformation and sliding screw bending were presented.The hysteretic properties,skeleton curves,strain changes and failure modes of the specimens under failure mode were studied by experiments and finite element studies.(4)Based on the results of the research group’s analysis of the mechanical properties of the self-resetting SMA support,this paper analyzes its ultimate bearing capacity,considering the same factors as the asymmetric connection.Through finite element parameterized simulation,the vulnerable region under loading was studied,and the difference between it and the asymmetric connection in mechanical properties and limit state was analyzed,and the different characteristics of the connection under failure were obtained.