| In the lateral force resistant system of steel structure,the eccentrically braced frames(EBFs)are combined with the advantages of the concentrically braced frames(CBFs)and the moment resisting frames(MRFs),and have favorable ductility and lateral stiffness,which become the preferred structural system in high seismic region.As a common D-type eccentrically braced steel frame,the link-to-column connections are very similar in design and construction to MRFs,so the damage of the welded beam-column nodes in the Northridge and Kobe Earthquakes will be generated in the link-to-column connections,and link is utilized by D-type eccentrically braced steel frame for seismic energy dissipation,therefore,the overall structural system seismic performance will be affected by the destruction of link-to-column connections.In this paper,a kind of D-type eccentric braced steel frame with additional double cover plate improved shear link was proposed.Reinforcement of link-to-column connections by using additional double cover plates,the plastic deformation of the link was far away from the node,so as to avoid link-to-column connections brittle damage and guarantee the excellent performance of eccentrically braced frames.The primary researching contents and achievements were as follows:Firstly,the self-compiled heat source subroutine DFLUX was called by ABAQUS platform,combined with live-die unit technology,the welding process was realized at the link-to-column connections,and the welding temperature field of the node was obtained.By using the method of thermal-mechanical coupling the welding residual stress were calculated.The differences of performances between the new system with double cover plates and the traditional system under two load modes were compared.The results showed that the new system is superior to the traditional one in bearing capacity and energy dissipation capacity under the monotonic loading;the each seismic resistance index of the new system was better than the traditional system,at the same time,the new system could achieve the purpose of plastic hinge outward displacement,and avoid the damage of the beam end weld under the cyclic loading.C yclic loading was carried out for the new system considering and without considering the welding residual stress.The comparison results showed that the each seismic resistance index of the new system with considering the welding residual stress was lower,which was closer to the real situation.Secondly,through the three groups of 18 specimens with considering the welding residual stress of the new system for the effects of shear and bending shear link on the parameters were analyzed.The changes of the parameters focused on the thickness of additional double-cover,length of the strengthen district and the link beam.Analysis results showed that: with the addition of double cover plate thickening,for the shear link,the bearing capacity was increased,the ductility was decreased,and the stiffness was not changed,the energy dissipation performance and plastic rotation angle increased first and then decreased;for the bending shear link,the bearing capacity,energy dissipation performance,plastic rotation angle were improved,the stiffness was not affected,but less impacted on the ductility.Therefore,it is suggested that the range of thickness of additional double plate is 0.75~1.25 times of web thickness of link.Besides,the 25mm~35mm gap is arranged between the additional double cover plate and top and down flange of link beam,so that it is convenient to construct.With the increase of the strengthen district,the bearing capacity,ductility,stiffness,energy dissipation performance and plastic rotation angle of the shear and bending shear link are reduced with varying degrees.Therefore,it is suggested that the length of strengthen district is in the range of 0.45 to 0.55 times of height of link or taking the required spacing between the stiffeners.With the increase of the length of link beam,the ductility,stiffness,energy dissipation performance and plastic rotation angle of the shear link show various degree of descending,but the influence on the bearing capacity was not prominent;for the bending shear link,the ductility,stiffness,energy dissipation performance and plastic rotation angle were also reduced with varying degrees,the influence on the bearing capacity was less.Therefore,it is suggested that the range of the length of link,shear link is 0.81~0.94 /P PM V,and bending shear link is 1.61~2.02 /P PM V.Finally,the whole simulation on the basis of the new system with residual stress was carried out by considering the composite floor.The analysis results showed that under uniaxial loading,the composite floor had little effect on the mechanical properties of the new system considering the residual stress.Under cyclic loading,concrete cracks first appeared in the upper part of link beam reinforcement area which close to the region of column,as the loading continuing,cracks appeared in the upper concrete corresponding to the link beam,which could be used to determine the location of the replacement or repair of concrete.Under cyclic loading,for the shear link,beginning stiffness and bearing capacity were increased with varying degrees,ductility,energy dissipation and plastic angle were decreased after setting composite floor;for the bending shear link,bearing capacity and beginning stiffness were increased,and plastic angle,ductility and energy dissipation performance decreased little. |
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