Experimental Study On Mechanical Properties Of Square Columns Strengthened With CFRP And CC Under Axial Compression

Carbon fiber reinforced composites(CFRP)have been widely used in a large number of practical projects because of their light weight and simple operation.When the amount of CFRP can meet the needs of engineering,the use of full wrapping will cause unnecessary consumption of CFRP,so the spacer strip wrapping is more advantageous.However,the durability and bearing capacity of the specimens are greatly affected because the concrete between strips is exposed to the air.Concrete canvas(CC)is widely used in engineering practice because it can directly cover the surface of various shapes like cloth and form a thin,fire-resistant and durable concrete slab after being watered and hardened.Therefore,in this paper,concrete canvas and CFRP strips are used to strengthen concrete square columns and the axial compression mechanical properties of concrete square columns strengthened by concrete canvas and CFRP strips are studied.Based on the axial compression test of concrete square columns strengthened with concrete canvas and CFRP strips,the effects of the restraint ratio of CFRP strips,the number of CFRP layers(1 layer,2 layers,3 layers),the strength grade of core concrete(C30,C40,C50),section shape and reinforcement on the axial compression mechanical properties of concrete square columns strengthened with CFRP strips are studied.The results show that: except for the weak restraint of ordinary concrete specimens,the joint reinforcement specimens are all strong restraint,and the bearing capacity and ductility are significantly improved compared with ordinary concrete;For the specimen with different external factors,the bearing capacity of the whole wrapped specimen is higher than that of the strip wrapped specimen,but the ductility is lower.After adding CC to the specimen,it can replace part of CFRP,reduce the wrapping amount of CFRP by 22%,and improve the bearing capacity of the specimen by 4.1%,When designing the strips,the width should not be greater than 1 / 9 of the column height,and the spacing should not be less than 1 / 9 of the column height.The three-layer CFRP is the best.The ductility of the specimens with strip restraint is better than that of the whole package,and the ductility of the specimens with fiber band restraint ratio of 0.33 ～ 0.50 is the best;For the specimens with different internal factors,the bearing capacity and ductility of the circular specimens are higher than those of the square columns.With the increase of concrete strength grade,the bearing capacity of the specimens’ increases,but the deformation capacity and ductility become worse.Compared with the specimens with unconstrained reinforcement,the bearing capacity and deformation capacity of the specimens with internal reinforcement become larger,and the internal factors change,It can improve the deformation performance of concrete in the strengthening stage,thus increasing the utilization rate of CFRP tensile strength.Based on the internal and external factors,the peak stress-strain model of CC + CFRP strip confined column is established.The fitting curve analysis shows that the formula has certain applicability.