Study On Seismic Performance Of FRP-strengthened RC Frame Joints

Non-ductile RC frames are designed without considering seismic load and canonly bear gravity loads; present seismic requirements cannot be satisfied due to therevision of design code. In recent years, many earthquake hazards resultsdemonstrate that the RC frame joints’ failure leads to local and also whole collapseof structures which cause lots of personal injury, death and loss of properties.Therefore, it is an urgent need to seismically strengthen the frame joints in a largenumber of existing non-ductile reinforced concrete frame structures. Fiberreinforced polymer (FRP) composites have been widely used for seismicstrengthening or rehabilitation of concrete structures in the past decades, due totheir light weight, high strength, and ease of application. There are a large numberof interior joints in RC frames. Due to the influence of slabs and orthogonal beams,the application of the strengthening method of this type joint is intricate to achieve.At present, study of FRP strengthened RC frame joints is focused on reduced scalebeam-column joints without slabs and orthogonal beams, whereas these jointscannot reflect the actual RC frame seismic performance. For this reason, this thesiscovers the quasi-static test research and finite element simulation analysis of the fullscale RC frame interior joints with slab and orthogonal beams. The main contents ofthis thesis are summarized as follows:(1) Quasi-static test was performed on four full-scale RC frame joints; thestudy focused on the seismic performance of RC frame joints, the influence of slaband orthogonal beam, and different strengthening techniques of using FRP. Theresults show that: due to the existence of slab, the beam bending stiffness has asteeper ascension; contrast specimen had a yield failure occurring in the uppercolumn plastic hinge area; orthogonal beam had a strong binding effect on joint corearea resulting in limiting the extension of crack effectively; different FRPreinforcement methods had bigger energy dissipation and ductility, but thedifference was not significantly large, in which FRP reinforcement wrapped only inthe upper and lower column plastic hinge zone was notably the most effective, theplastic hinge zone in the beam end at joint core failed first.(2) Using the normalization method，a comparison of the seismic performanceof cantilever column and upper column in the joint was performed. The resultsdepicted that: using existing cantilever column method for seismic performancestudy is only applicable to the bottom frame column in actual structure analysis, butcannot really reflect the standard layer column’s seismic performance; a contrast ofthe equivalent stiffness of the cantilever column and upper column in the joint, revealed a linear relationship, and was controlled by the beam line stiffness ratio.(3) Improved the modified compression field theory, determined the joint coreshear block material model and method, based on the OpenSees finite elementsoftware adopted Joint2D element which can consider the influence of sheardeformation to establish RC frame joint with slab finite element analysis modelbefore and after FRP reinforced, simulation results were in good agreement withthose obtained with the test, in order to establish FRP reinforced concrete framestructure with joint, finite element model laid the foundation.