Study On The Seismic Behavior Of The Improved Buckling Restrained Brace And The Energy Dissipation Mechanism Of Its System

Buckling Restrained Brace(BRB)is experiencing the development stage from the reinforced concrete restraint member to the concrete filled steel tube confined member and then to the whole steel restraint member,the theoretical research on the global stability and local stability of various types of buckling restrained brace has become more and more mature,What's more,it has been proved by the research of scholars in various countries.But in the context of this research,the buckling failure of the extended section of the buckling restrained brace occurs in the test,it may not be a design flaw,but caused by the defects of the end structure.Ordinarily,the damping effect of BRB is mainly realized in two aspects,first,the elastic stage provides additional lateral stiffness to reduce the displacement response of the structure;Second,it can provide additional resistance to the structure in the elastic-plastic stage to dissipate the seismic energy into the structure,so as to reduce the displacement response and shear response of the structure.Designers are often easier to handle the first situation,but the second situation's uncertain factors and influence factors are more than the first's.It is hard for designers to choose a appropriate BRB which intensity and rigidity matched to the structure.This is mainly because of they don't know the interaction law between BRB and structure.With the BRB system in engineering application in China is increasing,the researchers are more and more interested in the failure modes of buckling restrained brace structure under earthquake action and the failure mechanism of it,but it is a pity that,at present,the research on this field is less.Because the world is in the seismic active period,after earthquake,whether BRB can continue to work properly?How to evaluate and detect whether it can achieve the ability to continue working?Whether we need to replace it?What is the standard of the replacement?For all these studies,at present,in the academic field and engineering application is still in a blank.This paper mainly studies the BRB's ends improvement measures,the interaction mechanism of BRB and frame structure,and the BRB system's failure mode and failure mechanism.The main research contents and conclusions are as follows:(1)In the second chapter,because of the all steel BRB's extended connection's buckling failure,and the transition section between extended connection and the end of constraint component's structural defects,we proposes an improved structural measures which to improve the stability of overhanging connection.We made a Low cyclic loading test to all steel BRB which ends improved,results show that this improvement can effectively prevent the extended connection section buckling failure.The results of theoretical analysis show that excessive friction effect caused by contact between the core board and constraint component is not conducive to the local stability control support.The contact force along the axial direction is the distribution characteristics of both sides is big but the middle is small,and it increases with the increase of the axial load.Analysis of local buckling mechanism of BRB and the corresponding criterion of stability design.(2)In the third chapter,we studied the interaction mechanism between BRBs and reinforced concrete frames,and we revealed the energy dissipation mechanism of BRBs,and discussed the various stages of work in the main frame structure(elastic and plastic),the interaction between BRBs and the main frame structure.We found the BRB attached to the main frame's effective damping ratio variation and characteristics,attached and the influencing factors of the additional effective damping ratio was analyzed,the results lay a foundation for suggested values and design criteria for the fourth chapter.Meanwhile we studied the performance of all steel BRB which ends improved in the overall framework structure.Results shown that in the overall framework structure,improved BRB's extended connection also didn't behave any instability.(3)In the fourth chapter,we studied the interaction mechanism of BRB and reinforced concrete frames.According to the effective damping changes of BRBS add to main structure and characteristics,theoretical derivation of the BRB structure additional effective damping ratio formula,we analyzed the main frame in different working states(elastic and plastic),the factors that influenced the energy dissipation capacity of BRB,based on the analysis results,we gave the recommended values of additional damping ratio and the BRB design discipline matching with structural parameters.According to the BRB's different engineering application model and system structure were different,we made the theoretical derivation of the BRB energy earthquake energy and rare earthquake safety conditions.(4)In the fifth chapter,we made a shaking table test to BRB frame structure of reinforced concrete,and we revealed the failure mechanism and failure mode of the structure under earthquake,studied on the energy dissipation characteristics of the structure system from the view of energy,researched and analysis of the change in performance before and after the earthquake of BRBs,evaluated the BRB's persistently working ability after the earthquake,introduced the related principle and technology about how to use the MATLAB to deal the shaking table test data,finally we discussed how to evaluate and test BRB's performance and the corresponding replacement criteria after the earthquake.