Research On The Mechanical Properties Of CFRP Confined Concrete Under Long-Term Load

FRP(Fiber Reinforced Plastics) confined concrete can effectively improve the strength and ductility of concrete columns members. In the past few decades, while domestic and overseas scholars have carried out a large amount study on the mechanical properties of FRP confined concrete under short-term load, in the actual application, before confined by FRP sheet, there is already some non-ignored axial strain in the concrete column. Meanwhile, Long term load will apply on the concrete column after the reinforcement process. Under the above mentioned considerations, In order to have a better prediction about the FRP confined concrete in practical projection, it is necessary to conduct a study about FRP confined concrete under long-term load.Creep phenomenon will occur in concrete and FRP sheet under long-term load, in order to get an accurate prediction about the mechanical properties of FRP confined concrete under long-term load, it is necessary to study the:(1)the creep and shrinkage phenomenon in concrete;(2)creep phenomenon in FRP;(3)the mechanical properties of FRP confined concrete under short-term load. Based on this line of reasoning, the main research contents of this paper contain the following points:Four frequently-used concrete creep, shrinkage prediction models were compared according to RILEM test database, stimulation results show GL2000 models and B3 model has a relatively high accuracy, and GL2000 model is more suitable for numerical simulation analysis; based on the collected data of CFRP (Carbon Fiber Reinforced Plastics) creep, Findley model was modified to reach an accurate prediction about CFRP creep.Numerical stimulation was conducted on CFRP confined concrete under short-term, simulation and experimental results were compared to show that the incremental iterative method can be used to predict the stress-strain curve relationship of CFRP confined concrete with sufficient accuracy. (2)The axial-lateral strain relationship of CFRP confined concrete has relatively large impact on the stimulation results. Among the collected axial-lateral strain relations, Teng J G formula has a relatively high accuracy.Under the overall consideration of the creep and shrinkage in concrete, the creep in CFRP, and the numerical analysis process of CFRP confined concrete under short-term load, a numerical stimulation which is based on MATLAB was presented to predict the mechanical properties of CFRP confined concrete under long-term load. The simulation results show that: (1) under the premise of keeping load level unchanged before and after CFRP reinforcement, actual efficiency of CFRP confined concrete is relative low, the Lateral restraint force in FRP sheet under long-term load is merely about 20% to 30% of the ultimately lateral restraint force. (2)Due to the insignificant lateral stress, the axial-time relationship of CFRP confined concrete seems unchanged after CFRP reinforcement, which can be predicted by GL2000 model with efficient accuracy. (3) The creep phenomenon will increase the elasticity modulus of CFRP, and reduce the ultimate strain in CFRP sheet, then will in turn effect the overall performance of CFRP confined concrete after long-term load. The stimulation results show that the peak-stress of CFRP confined concrete mainly remained unchanged after long-term load, however, the peak-strain reduced relative obviously after long-term load. Both of them will affect the long-term performance of CFRP confined concrete.