Study On Mechanical Properties Of Concrete Circular Column Confined By HFRP Under Axial Compression

Due to the existing building structural performance deterioration of existing building caused by reinforcement corrosion, material aging, overload and natural disasters, it needs a huge of money to repair them every year. In order to overcome these problems, scholars both at home and abroad have done a lot of research work. Because fiber reinforced composites (FRP) have the advantages of light weight, high strength, easy construction, corrosion resistance and little influence on the original structure stiffness, it has attracted the attention of scholars at home and abroad, so the FRP reinforcement concrete structure become research hotpot in civil engineering. But research shows that single fiber is very brittle and the deformation capacity is insufficient, so the ductility of reinforced structure is very poor which restrict the widespread application of FRP. Hybrid fiber can take full advantage of different fibers, foster strengths and circumvent weaknesses, improve the ductility of structure and optimize the comprehensive mechanical properties of FRP.In this paper, the mechanical properties of HFRP and concrete columns confined by HFRP were studied by experiments. By means of experiments and theoretical analysis, the elastic modulus and tensile strength were studied. The author analyzes the compression strength, ultimate longitudinal strain, circumferential strain, failure mode and strengthening cost. Finally an overall stress-strain model was proposed according to summarize and regression of experimental data.The mechanical properties of different kinds of HFRP composed by CFRP, BFRP and GFRP were studied. Experimental results show that the elastic modulus accords with mix law while the tensile strength changes with the content of fiber with lower ductility.The failure mode, bearing capacity, and strengthening cost were analyzed based on the unaxial compression test of concrete columns. Testing results show that the cracks of concrete columns confined by HFRP develop very slowly, and it appears no blowout. When the specimen failure, fibers inner and outer fracture at different places. It can be seen that lots of inner fibers were pulled out. The inner fiber appears high strength than signal fiber. HFRP can reduce the reinforcement cost on the premise of guarantee the strength. When the fiber layers increase, the compression strength and ductility of specimen also increase. Due to the influence of fiber bond and overlap between different fibers, hybrid effect is not very good so it should not be used in civil engineering.It can be seen from the analysis of stress-strain curve development that concrete strength, FRP stiffness and intensity are three critical parameters which decide the curve. Based on the summary and analysis of existing models and test data, a stress-strain model of HFRP confine concrete was proposed in this paper. Comparing with the experimental data, the model agrees well with the experimental data.