Behaviour of FRP-reinforced concrete beam-column joints

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Corrosion of steel reinforcement has led to high maintenance and repair cost for concrete structures especially those built in harsh environments. Recent research indicated that the individual concrete members (beams, slabs, and columns) reinforced with the non-corrodible fibre reinforced polymer (FRP) composite bars behaved well under both monotonic and cyclic loading conditions. However, very limited work was conducted on the connections (joints) of these individual members to form a frame structure. Joints are required to function as restraint to adjoining column and beam members and develop their full inelastic capacity if necessary. Since FRP bars have a linear elastic behaviour till failure and show reduced strengths when bent or subjected to compressive stresses, there are concerns on the ductility performance and the integrity of such joints when FRP bars are use, especially under seismic loads. This research program will focus on investigating the behaviour of FRP-reinforced concrete beam-column joints. The research program consists of laboratory investigation and analytical modelling. Full-scale FRP-reinforced concrete beam-column joints (interior and exterior) will be tested in the laboratory. The test parameters will include the type of loading (monotonic or cyclic), the amount of confinement for the joint core (bar diameter and spacing of FRP stirrups), column axial load, concrete strength, FRP main reinforcement type and ratio, and detailing of reinforcement. Nonlinear finite element analysis will be used to model the complex distribution of stresses and strains at the joint panel in lights of the essential differences in mechanical properties and bond characteristics between FRP and steel bars. This model will be incorporated into a computer code, which will be calibrated against the experimental results. Then, the computer code will be used to perform parametric studies to investigate a wide range of factors that are expected to affect the behaviour of such joints. The test results will be formulated into design equations for ductile and integral beam-column joints. This research leads to new structures with improved performance, better durability and less life-cycle cost.