Flexural Behavior Of Reinforced Concrete Beams With CFRP Tubes Confined Compression Zone

The ductile deformational capacity of reinforced concrete(RC) beam has significant influence on the seismic performance of RC structure. The reinforcement ratio is strictly limited by?Code for seismic design of buildings GB50011-2010?to guarantee the ductility of RC beams. However, in actual design, engineers have to adopt the high reinforcement ratio beam or over-reinforced beam due to the height limit or excessive loads on structure. Ductility is usually judged from four levels, ie.structure, member, section and material. The ductility of members is closely related to the ductile behavior of sections and materials. RC beams are made of concrete and steel bars, and steel bars have a good ability of deformation, therefore the ductility of the RC beam is mainly controlled by the ductility of concrete. The strength and the ultimate compressive strain of concrete can be enhanced by applying lateral restraint on it. So, the ductility of RC beams can be improved by applying lateral confinement on concrete in the compression zones. CFRP(Carbon Fiber Reinforced Plastic) has many advantages, such as light weight, high strength, high elastic modulus, and corrosion resistance et al. CFRP confined concrete showed good deformation ability in tests. In this context, a new type of RC beam with CFRP confined compression zone was proposed. Flexural behavior of CFRP confined beams were investigated by experiments, which were conducted on 9 CFRP confined beams and 3 comparative beams. The main works of this paper are as follows:(1) Mechanical performance tests were conducted on materials which would be used in the experiments, including CFRP sheet uniaxial tensile test, steel bar tensile test, and mix design and compressive test of C35 and C50 concretes, which provided evidence for the experimental study and theoretical analysis of the CFRP confined beam.(2) Flexural behavior of CFRP confined concrete beams were researched by means of four-point bending static load tests. Five parameters, ie. concrete grade,reinforcement ratio, CFRP layer, length and shape of confined zone were taken into consideration. Results indicated that ductility of RC beams were effectively improved with the help of confinement due to the CFRP tubes, nevertheless, the flexural capacity was little influenced. As far as the ductility was concerned, the higher grade the concrete was, the less ductility improvement CFRP confined beams got; the higherreinforcement ratio was, the more increasement achived. It was noticed that increasing the CFRP layer didn't help to enhance the ductilie behavior of CFRP confined beams further, but it postponed the strain development of CFRP tubes. We also found that rectangular CFRP tubes worked more effitively than rounded CFRP tubes when used in beams. Extending the constrained region aimed at perfecting the flexural property was in vain.(3) According to the material mechanics performance test results and the simplified stress-strain relationship, combined with the existing CFRP confined concrete stress-strain model, nonlinear analysis of flexural behavior of CFRP confined beams were carried out, in which moment-curvature relationship of setion and load-deflection curve were emphatically investigated. The calculation value matched well with the experiment data.