Study On The Joint Mode And Mechanical Property Between The External BRB Frame And The Existing RC Frame

Yunnan Province is situated on the southwestern frontier of China,where is the seismic hazard area.A large number of existing buildings,especially middle school buildings and hospital buildings,don’t meet the current requirements of the seismic code.Most of these buildings are in the form of reinforced concrete frame structures,which are suitable to adopt bucklingrestrained brace to retrofit.Taking a hospital building in Qujing city,Yunnan Province as an example,this paper simulates the seismic performance of the external buckling-restrained brace frame reinforcement scheme by finite element analysis software,then analyzes the difference between the rigid-joint and the flexible-joint in the connection design of the external structure and the original structure,finally a new connection design is proposed as reference for subsequent seismic retrofitting engineering of analogous buildings in Yunnan or other hazard areas.The calculation find that the seismic capacity of the original structure was insufficient,and after considering several factors,an external buckling-restrained brace frame was used for reinforcement engineering.After retrofitting,the analysis revealed that the structure’s torsion effect is controlled,inter-story displacement is decreased,seismic shear force increases,moreover the greater the intensity of the seismic,the more obvious the effect of improvement;the yield mechanism of the existed structure,“strong beam and weak column” and “ interstory yield”,and collapse resistance are improved;and the BRBs undertake considerable seismic energy,improve the energy-consuming capacity of the structure,reduces the seismic response.Above of these illustrate that the reinforcement scheme is excellent.In order to study the advantages and disadvantages of rigid-joint and flexible-joint in the connection design of the external steel frame and the original structure,time history analysis,static and dynamic elastoplastic analysis are carried out.The analysis results found that the rigid-joints are better than the flexible-joint in most of the indicators such as inter-story shear force,hysteretic energy and collapse resistance.Combining the Pushover curve and the IDA curve can explain this conclusion more clearly,so during the design and the construction,the rigid-joint connection between the external structure and the main structure should be achieved as much as possible.Based on the above analysis conclusions,this paper proposes a rigid-joint form of the implanted bar and simulates the shear failure process under the horizontal seismic by carrying out the finite element analysis on the connection part.It is found that the shear strength of the connection part is mainly related to the number and the diameter of the implanted bar.Additional structural measures such as adding steel plates can also effectively improve the shear strength of the connection part,the concrete material strength of the existing structure has little effect.The outer side of the planted bar group bears the larger force,whose bottom is the weakness under the seismic.Protective measures can be taken to enhance the shear resistance of the planting bars,so as to ensure the safety of the connection part.