Research On Axial Compression Performance Of Pre-cracked RC Columns Strengthened By Round Steel Casing And Steel Fiber Cement Mortar

Round steel casing-steel fiber cement mortar outsourcing reinforcement RC column is a new type of reinforcement technology.Steel fiber cement mortar has a significant improvement in toughness,crack resistance and ductility over ordinary concrete mortar,and the strength and ductility of steel casing reinforced concrete columns has been improved to a large extent.At present,domestic and international research on this method mainly focuses on the performance of unpre-damaged components after reinforcement,while research on the reinforcement of components with different degrees of damage is still relatively lacking.In this paper,the percentage of the peak load of the pre-loaded ordinary reinforced concrete column is mainly used as the damage index of the column:60%of the ultimate load is primary damage,80%is secondary damage and 100%is tertiary damage.A total of seven specimens were designed,and the axial compression test of the damaged columns strengthened with steel casing steel fiber cement mortar was carried out with steel casing diameter thickness ratio,damage degree of RC Concrete and dispersion of the damaged columns as the influencing factors.The research results obtained are as follows:(1)Designed and fabricated seven pre-damaged RC columns for axial compression test and analysis,and analyzed the RC column’s force failure process and failure morphology under axial compression.Data were collected through tests to analyze the load-displacement curves of pre-loss RC columns and the load-strain curves of reinforcement bars and hoops.(2)A new outsourced reinforcement technique was used to study the axial pressure performance of seven pre-damaged RC columns,analyzed the force damage phenomenon and damage characteristics of the specimens,and analyzed the load-displacement curve,load-strain curve and transverse deformation coefficient of the specimens in combination with three influencing factors,which showed that the design parameters with significant influence on the composite reinforced pre-damaged RC columns were the diameter-thickness ratio of steel sleeve pipe and the degree of RC concrete damage.(3)Based on the principle of superposition and ultimate equilibrium,the formula for calculating the axial pressure bearing capacity applicable to the pre-damaged RC column of steel casing-steel fiber cement mortar outsourced reinforcement is proposed,and the theoretical calculation value is in good agreement with the actual test value,which can provide reference for the application of steel casing-steel fiber cement mortar in engineering.