Research On Seismic Behaviors Of Sub-frame Beams Of Buckling-restrained Braced RC Frame Based On Damage Conctrol

Earthquakes as a natural disaster will cause serious casualties and property losses,Buckling-restrained braces(BRB),as an energy dissipating brace,has become one of the important means of structural energy dissipation and vibration reduction.In recent years,it has been more and more widely used in new RC frame structures or retrofitted RC frame structure.The addition of BRB can significantly reduce the seismic response of the main frame structure,thereby effectively preventing the main frame structure from being severely damaged or collapsing under a severe earthquake.At present,the RC frame design mainly considers the adverse effect of brace additional axial force on the seismic performance of the sub-frame.However,under the severe earthquakes,the subframe also bears the influence of brace additional bending moment and frame action effect.As a result,the actual mechanical states of the sub-frame may be significantly different from that when only the additional axial force is considered,which may cause the sub-frame to destruction before the BRBs.In addition,when the traditional gusset plate connection method is adopted,the mechanical state of the sub-frame structure is relatively complicated,which makes its damage difficult to be accurately predicted and controlled.Therefore,this paper proposes a design concept of RC sub-frame based on damage controll,which is by the combination of sliding gusset plate connection and sub-frame beam-column damage control method.Then by three BRB RC beam-column subassemblage quasistatic experiments,corresponding numerical simulation and parameter analysis,verifying the effectiveness of the damage-controllable design idea of the sub-frame.The main contents and conclusions of this study are as follows:(1)When analyzing the traditional gusset plate connection method in Chapter 2,it is found that the sub-frame beams and columns are subjected to complex mechanical states.On this basis,a sliding gusset plate connection mothed is proposed to effectively simplify the mechanical states of the RC subframe beams and columns;In order to effectively control the sub-frame beamcolumn damage,based on the mechanical state of the sub-frame beam-column under different interactions between the gusset plate and the sub-frame beam-column,the mechanism of plastic hinges transfer in the adjacent beam section of the gusset plate is analyzed,and the design method of moving the plastic hinge to the end of the gusset plate is proposed under different connection structures,and proposing to strengthen the stirrups of the expected plastic hinge position to ensure that the plastic hinge has sufficient ductility;on this basis,the softened strut-and-tie model is adopted for the shear capacity design of the discontinuous area(zone D)of adjacent beams and columns of the gusset plate to ensure that zone D has good seismic performance.(2)In Chapters 3 and 4,in order to verify the effectiveness of the proposed sub-frame damage controllable design ideas,the full-scale beam-column subassemblage(one using traditional gusset plate connection and two using sliding gusset plate connection)were subjected to a quasistatic test.The test results showed that the sliding gusset plate connection can better release the deformation constraints of the RC beam and column,thereby effectively simplifying the mechanical states of the RC sub-frame beam,reducing the damage degree of the RC sub-frame beam,and effectively reducing the sub-frame difficulty in controlling beam-column damage;when the traditional gusset plate connection method and the sliding gusset plate connection method are used,improving the shear design of the anchor plate and the additional transfer plastic hinge longitudinal bars can effectively move the plastic hinge of the sub-frame beam to the gusset plate end,and the damage of the sub-frame beams is mainly concentrated on the plastic hinges of the beams outside the gusset plate;there is no shear failure and bending-shear failure in the D zone of the sub-frame beam,so the design is reasonable.(3)In Chapter 5,based on the results of quasi-static tests,ABAQUS finite element software was used to perform numerical simulation and parameter analysis on the seismic performance of RC sub-frame beams,and investigating the influence of the mechanical performance and damage of the RC sub-frame beam by the bolt pretension and the additional transfer plastic hinge longitudinal bars ratio based on sliding gusset plate connections.The numerical simulation and parameter analysis results show that the established finite element analysis model can better simulate the mechanical performance and damage degree of the RC sub-frame beam;the pretension of the bolt will significantly affect the tangential constraint between the gusset plate and the sub-frame beam and column.In the sliding connection configuration adopted in this study,it is reasonable that the bolt pre-tension is 0.3 times the bolt pre-tension specified in the specification.The larger reinforcement ratio of the longitudinal reinforcement used to transfer the plastic hinge will make the adjacent beam-column area of the joint plate show a certain integrity.The design method adopted in this study is conservative.The research results in this study will help to give full play to the energy dissipation and damping effect of the BRB on the RC frame structure,and provide more reliable scientific basis and theoretical guarantee for the safety of the energy dissipation and damping structure in severe earthquake-prone rigions in China.