Research On Seismic Behavior Of Low Yield Replaceable Links For Eccentrically Braced Steel Frames

In the traditional eccentrically braced steel frame,the energy dissipation beam section and the cross beam are a whole.Under the action of moderate earthquake and strong earthquake,the energy dissipation beam section as the first seismic defense line of the structure first absorbs energy to yield,because the material of the energy dissipation beam section is the same as the other members.In order to achieve the first yield of the energy dissipation beam section under the action of moderate and strong earthquakes,the designed result is usually to reduce its size.However,the yield point of low yield point steel itself is lower,and it is used as energy dissipation member in steel plate shear wall,buckling bracing and damper.At present,it has not been used as energy dissipation member in eccentrically braced steel frame.For this reason,this paper presents a kind of eccentrically braced steel frame system with low yield and can be replaced by energy dissipation beam segment.On the premise of ensuring that the size of energy dissipation beam section is not reduced,the low yield point steel is first proposed to be used in the energy dissipation beam segment of eccentrically braced steel frame.To provide theoretical support for future engineering practice.The alternative form is web bolt connection to separate out the energy dissipation beam section in the crossbeam.Under the action of moderate and large earthquakes,the plastic failure is concentrated in the energy dissipation beam section,which greatly improves the difficulty of restoration after the disaster.In this paper,the finite element model of eccentrically braced steel frame of low-yield and replaceable energy-consuming beam is established by means of finite element method,and the seismic performance analysis is carried out.The main research contents and results are as follows :Firstly,the feasibility of eccentrically braced steel frame with low yield and energy dissipation is analyzed.The stress process of the low yield system under the action of no earthquake,small earthquake,moderate earthquake and strong earthquake is studied,and the index verification is carried out in combination with the relevant codes.The results show that each component of the low yield system is elastic under the action of no earthquake or small earthquake,and the web of the energy dissipation beam of the low yield system first enters the yield under the action of moderate earthquake.Then the plastic region developed rapidly along the web length,but not destroyed,while the rest of the components remained in the elastic stage,and the web of the energy-dissipating beam section first reached yield under the action of a large earthquake.The other members remained in an elastic state,and then the plastic hinge began to develop in the middle of the beam section,and the maximum stress bolt also entered the yield.The rest of the members still did not yield.Then the plastic hinge was fully developed in the web of the beam section,and the whole web was completely yielding.Finally,three plastic hinges were formed in the middle of the two columns and at the right end of the beam.The displacement angle between the lower layers of the low yield system does not exceed the specified limit value,which proves that the system is feasible under the action of no earthquake,small earthquake and moderate earthquake.Secondly,five groups of 15 components are used to analyze the parameters of shear low yield system.The parameter variables are: energy dissipation beam length,web thickness,stiffening rib spacing,low yield point steel grade and axial compression ratio.The results show that with the increase of the length of the beam section,the energy dissipation capacity and stiffness of the shear model decrease in varying degrees,and the bearing capacity tends to increase first,but the ductility and plastic rotation ability of the model are less affected.It is suggested that the length of shear energy dissipation beam should be in the range of 1.01~1.14MP/ VP.With the increase of the thickness of the web of shear type energy dissipation beam,the energy dissipation capacity of the model first increases and then decreases,the bearing capacity decreases first and then increases,and the thickness of the energy dissipation beam web should not be too thick.The ductility has little effect on stiffness and rotation capacity.Therefore,it is suggested that the web thickness of the energy dissipation beam section of the double channel steel should be taken as 0.78~1.0times of that of the cross beam,and the energy dissipation capacity of the model would first increase and then decrease,while the stiffness would not change,and the ductility and rotation capacity would be improved by increasing the spacing of the stiffening ribs of the energy dissipation beam section.The bearing capacity is reduced to some extent.Therefore,it is suggested that the distance between stiffening ribs should be 0.33~0.42 times the height of the energy dissipation beam section,and with the decrease of the yield point of the low yield point steel in the energy dissipation beam section,the energy dissipation capacity and rotation capacity of the model will be increased to varying degrees,and the bearing capacity and stiffness will decrease.Ductility decreases first and then increases.In a comprehensive comparison,it is suggested that 225 grade low yield point steel should be used for the material of the energy dissipation beam section.With the decrease of axial compression ratio,the energy dissipation capacity and the bearing capacity of the model decrease first and then increase,the stiffness decreases first and then remains the same,and the ductility increases.The rotation ability is reduced.To sum up,the suggested value range of axial compression ratio is 0.6~0.75.Finally,the dynamic performance of a four-layer shear low yield system is analyzed.The results show that the effect of seismic action on the first five modes of shear system first increases and then decreases,and under the loading of Tianjin wave,Tangshan wave and artificial wave,the maximum interlaminar displacement angle of shear low yield system appears in the second layer.The peak value of column bottom shear force and the positive and negative extreme value of interstory displacement appear in the 1.5s~5s band,and the elastic-plastic displacement angle is less than 1/50 required by the code,which indicates that the anti-lateral capability of the structure under these three waves can meet the requirements of the code.The maximum stress of the structure appears in the bolt part,and does not reach the yield stress of the bolt.Under the action of Tianjin wave,the middle of the web of the energy dissipation beam section enters into the yield state,and the whole web of the energy dissipation beam section enters the yield state under the action of Tangshan wave and artificial wave.The rest of the components are in elastic state,which is consistent with the conclusion in Chapter 3,which proves the reliability of the conclusion in Chapter 3.