Seismic Performance Of RC Beam-column Joints Strengthened Using CFRP-UHPC Composite Panels

The reinforced concrete(RC)frame joint is the force transmission hub of the frame building and plays a role in maintaining the integrity of the structure.However,the RC frame joints designed according to early specifications generally have problems such as insufficient configuration of stirrups within the core or poor anchorage of longitudinal reinforcements.Under the action of earthquakes,joint shear failure is prone to happen and cause damage or even collapse of the building.The RC frame structure is adopted widely.Thus,joint diagnosing and strengthening its joint is a strategic requirement to realize the sustainable development of the construction industry.Traditional RC joint strengthening methods have disadvantages such as poor durability,low applicability,long construction period or large environmental interference.Therefore,it is necessary to put forward a green and efficient joint strengthening method.Ultra-high performance concrete(UHPC)is a fiber-reinforced cement-based composite material with strain hardening characteristics,high durability and high compressive strength.It can be combined with CFRP bars,which is high-strength,brittle,and poorly heat-resistant to obtain better complementary performance.With high strength,high toughness and high durability,UHPC prefabricated panels reinforced with CFRP bars have the advantages of wide application range,low environmental interference and low maintenance cost.Therefore,based on the seismic design concept of plastic hinges relacation,this paper carried out a study on the seismic performance of the RC frame joints strengthened using prefabricated CFRP-UHPC composite panels.First,based on the existing test data,a calibrated nonlinear finite element model was established,and the influence of the main parameters of CFRP-UHPC composite panels on the seismic performance of RC frame joints was explored.Then,the seismic design method to strengthen the RC frame joints with CFRP-UHPC composite panels is proposed,which provides a theoretical basis for its engineering applications.The main research contents and results are as follows:(1)The constitutive model of related materials was summarized and analyzed,and based on the DIANA finite element software,three sets of existing test data were numerically simulated,which verified the accuracy of the constitutive model selected for simulation(2)Based on the non-linear finite element model corrected by the experimental data,the whole loading response of the RC joints were simulated and analyzed,and the effects of variables on the seismic performance of joints were also studied,including the thickness of the UHPC precast slab,the area of the CFRP reinforcement,the extension length of the composite slab,the UHPC strength,the strength of the base concrete,and the column-beam flexural strength ratio.The results show that through reasonable design,the CFRP-UHPC composite panel can enhance the shear strength of the joint,avoid shear damage,and realize the beam hinge relacationt,thereby effectively improving the seismic performance of the joint.(3)Based on the equivalent rectangle method and the modified softened strut and tie model,the bending and shear design formulas for the beam and joint strengthened using CFRP-UHPC composite panels are derived respecitively,and verified by experimental data and finite element results.On this basis,the seismic design method to strengthen the RC frame joints with CFRPUHPC composite panels is proposed,which can provide a theoretical basis for engineering applications.