Seismic Performance Analysis Of New Type Of Outsourcing Anchored Joint Steel Structure Adding Hybrid Structure

In the story-adding reconstruction of existing buildings,steel structures have been widely used due to their unique advantages.However,the hybrid structure formed has obvious vertical mass and stiffness mutation problems.The connection joints between the upper and lower structures have less constraint on the story-adding part,and there is obvious whiplash effect,which makes the overall collaborative seismic performance of the hybrid structure poor.In this regard,the new type of outsourcing anchored joint proposed by the research group is applied to the hybrid structure of steel structure.The seismic performance of the structure is studied by using the finite element method through unidirectional loading and horizontal cyclic loading.The specific research contents and results are as follows:(1)Verify the correctness of the finite element model of the new type of outsourcing anchored joint.The finite element model of the new type of outsourcing anchored joint was established by ABAQUS software.The force transmission path and failure mechanism of the joint under cyclic loading are analyzed and compared with the experimental results.The results indicate that the failure phenomenon of the join simulated by the finite element is basically consistent with that of the test,which is plastic hinge failure at the end of the beam.The load-displacement curve is in good agreement.The load and residual stiffness errors are less than 10%at each characteristic point,which are within a reasonable range.The finite element model has certain reliability.(2)Verify the correctness of the finite element model of the steel structure adding layer hybrid structure with traditional implanted reinforcement joint.The finite element model of the traditional implanted reinforcement joint hybrid structure was established,and the low cyclic reciprocating loading was carried out.Compared with the experimental results,it shows that the failure characteristics of the finite element model are basically the same as those of the test,which are all mixed hinge failure.The bearing capacity of the structure is lost due to the formation of the plastic hinge at the bottom column foot at last.The errors of the load at each characteristic point and the positive and negative stiffness degradation rate are less than 10%.Meanwhile,the sequence of the plastic hinge formation shows no difference with the test.The finite element model has certain accuracy and can be used for subsequent research.(3)Study on seismic performance of hybrid structure with new type of outsourcing anchored joint.Based on the above-mentioned correct finite element modeling method,a new type of outsourcing anchored joint for hybrid structure model is established.Unidirectional loading and horizontal cyclic loading are carried out on the structure to study its nonlinear mechanical performance,and a comparative study is carried out with the hybrid structure with traditional implanted reinforcement joint.It turns out that the failure mechanism of the two specimens was mixed hinge and the structural failures were caused by the plastic hinge of the middle column foot on the first story.The plastic hinge at end of the beam of hybrid joint on second story moves outward when the hybrid structure with new type of outsourcing anchored joint is damaged,which effectively protects the core area of the joint from damage.The plastic strain of the lower concrete frame is larger,and the stress of the steel column is significantly reduced.The initial stiffness,bearing capacity,energy dissipation capacity and collapse resistance of the structure are improved to varying degrees.The stiffness mutation at the added layer structure and the"whipping effect" at the top layer are smaller,which makes the overall cooperative work performance of the structure better and meets the seismic design requirements of "strong joints and weak components".(4)Study on the influence of relevant parameters on seismic performance of hybrid structure with new outsourcing anchored joint.The extended analysis is carried out by changing the mass ratio and stiffness ratio of the upper and lower structures.Results are as follows:①Increasing the upper and lower mass ratio of the hybrid structure has no impact on the position of the "weak layer",but it can slightly improve the overall stiffness of the structure.The larger the mass ratio,the faster the overall stiffness degradation,and the smaller the final residual stiffness,the lower the structural bearing capacity.When the mass ratio is greater than 0.333,the "whipping effect"of the top layer of the hybrid structure is significantly reduced and the overall deformation is more coordinated.However,without strengthening the substructure,the failure rate of the hybrid structure is accelerated,and the bearing capacity decreases rapidly after the plastic hinge appears in the structure.Moreover,there are more plastic hinges at the column end,which is not conducive to seismic resistance.②Compared with the H-shaped steel column hybrid structure,the hysteretic curve of the box-shaped steel column hybrid structure with better out-of-plane stability is more plump,and the bearing capacity,overall stiffness,ductility and energy dissipation capacity are improved to varying degrees.The overall lateral deformation of the structure is more coordinated,and it has better seismic performance.The upper stiffness is increased and the "whipping effect" of the top floor is obviously reduced by adding support.The bearing capacity,overall stiffness,residual stiffness,ductility and energy dissipation capacity of the hybrid structure are greatly improved.At the same time,it changes the internal force distribution of the structure and moves down the position of the "weak layer",which has a great adverse effect on the mechanical performance of the lower concrete frame structure and cannot improve the overall cooperative work performance of the hybrid structure.