| As an energy dissipation device,Buckling-Restrained Brace(BRB)has good hysteretic performance and energy dissipation capacity.It can ensure that the main structure will not be seriously damaged under earthquake,so it is widely used in building structure.However,it is found that the subframe structure strengthened by BRB is difficult to achieve the expected Seismic Target under large earthquakes.The performance is that the subframe beam and column are damaged before BRB.The reason is that only the influence of BRB additional axial force on subframe beam and column is considered in the engineering design,and the comprehensive influence of BRB additional bending moment and opening-closing effect of node(additional force of BRB)is ignored.When the traditional gusset plate is used to connect the BRB to the subframe,the strong constraint makes the stress in the adjacent beam and column area(Dregion)of the gusset plate more complex,and the failure mode and damage degree are difficult to predict and control.But the sliding gusset plate connection can release the tangential constraint between the gusset plate and the subframe beam and column to simplify the stress state in D-region,and then control the failure mode of the subframe beam and column.Therefore,this paper is based on the connection of sliding gusset plate,firstly,through the finite element numerical simulation analysis,the influence of the additional force of BRB on the mechanical performance of RC subframe beam and column when using different sliding connection structures is clarified,and the reasonable structure of sliding gusset plate connection is determined.Then,the shear design of the D-region of the beam is carried out based on the tension compression bar model and the corbel design theory.By comparing and analyzing the failure modes of the D-region of the subframe beam with different parameters,the best shear design method is explored.Finally,on the basis of ensuring that only bending failure mode occurs in the D-region of the beam,the failure mode of the plastic hinge area of the beam is controlled.The main contents and conclusions of this paper are as follows:(1)In Chapter 2,it’s the first thing to clarify the influence mechanism of the additional force of BRB on the stress state and failure mode of RC subframe beam and column under large earthquake through theoretical analysis.Then,the failure modes of subframe beams with traditional gusset plate connection and sliding gusset plate connection are compared to verify the effectiveness of sliding gusset plate connection to reduce the opening-closing effect.Finally,the numerical analysis model is established by using ABAQUS finite element analysis software with reference to the previous tests of the research group,The test results and finite element analysis results of the two groups of specimens are compared and analyzed respectively,and the error analysis is carried out.Generally speaking,the simulation results are in good agreement with the test results.The finite element modeling method used in this paper can provide theoretical support for the parameter analysis and judgment of beam failure mode in the following chapters.(2)In Chapter 3,the parameters are analyzed respectively such as the stiffness of the gusset plate,the rubber friction coefficient,the structure of the steel strips and the position of the plastic hinge,and the effects of these parameters on the mechanical properties of the subframe beam and column,the steel strips and the gusset plate are investigated to determine the reasonable sliding corner structure.The analysis results show that the increase of the stiffness of the gusset plate will make the adverse effect of the opening-closing effect of the node more obvious.Therefore,on the premise of meeting the strength requirements,the stiffness of the gusset plate should be as small as possible;The small friction coefficient of the rubber friction layer material is conducive to the control of the failure mode in the D-region of the beam.At the same time,the adjacent area and the end area of the gusset plate need to be designed for enhanced shear resistance;The outermost steel strip of the embedded part is most affected by the opening-closing effect of the node,so it only needs to double its thickness,while other steel strips still meet the strength according to the design requirements;The transfer of the plastic hinge position to the beam section at the end of the gusset plate is more conducive to the BRB force transfer and the control of the failure mode of the subframe beam.Under the typical IDR(1%,2%,3%),the shear force of the subframe beam with the plastic hinge outward moving is13.6% larger than that of the beam without outward moving.Therefore,when an appropriate amount of additional longitudinal reinforcement is configured to ensure that the plastic hinge is transferred out of the beam D-region,the shear design of D-region needs to be strengthened.(3)In Chapter 4,firstly,the mechanical performance and failure mode of subframe beam D-region are analyzed by finite element method,mainly exploring the effects of concrete strength,stirrup characteristic value of beam D-region,reinforcement ratio of longitudinal reinforcement,support yield axial force and relative position of additional transfer plastic hinge longitudinal reinforcement on the mechanical performance of subframe beam D-region,steel strips and gusset plate,and clarifying the influence law of the above research parameters on the failure mode of beam D-region.The analysis results show that the shear resistance of subframe beam in D-region mainly depends on concrete,and there is the optimal strength C40,while the reinforced shear capacity of stirrup in D-region is limited;The increase of longitudinal reinforcement ratio will significantly increase the beam shear.Under the typical IDR,the shear of subframe beam with longitudinal reinforcement ratio of 0.97% is 79.0% higher than the average of reinforcement ratio of 0.40%,which is very unfavorable to the control of beam failure mode;The increase of the yield axial force of the brace will significantly improve the shear demand in the D-region of the beam;As the additional longitudinal reinforcement shifts to the center of the beam,the shear bearing capacity of D-region increases and the flexural bearing capacity decreases,which is not conducive to the control of failure mode in D-region.the additional longitudinal reinforcement should be evenly arranged within the height of the beam section.(4)In Chapter 5,according to the parameter analysis results in Chapter 4,the model of beam D-region is established with reference to the corbel member theory in ACI 318-19,and the failure mode is analyzed.The results show that the theory can control the bending failure mode in D-region.on this basis,the beam shear span ratio is increased,and the reinforced shear design of beam plastic hinge area is carried out at the same time.It is found that the beam shear force will be significantly reduced,The plastic hinge zone gradually changes from bendingshear failure mode to bending failure mode. |
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