Study On Flexural Behavior Of Concrete Beams Strengthened By CFRP With Coupling Damage Of Load And Environment

In practical engineering,reinforced concrete beam work under the coupling action of two or more factors,such as load and environment.However,the research of scholars at home and abroad mainly focuses on the degradation of flexural performance of damaged beams and damaged beams strengthened with CFRP under the influence of mechanical damage under load or corrosion of reinforcement under environmental erosion.This is not consistent with the external stress state of the actual structure.Therefore,it is of great significance to study the degradation of flexural behavior of coupled damaged beams and coupled damage beams strengthened with CFRP.Based on the experimental research and the existing theoretical formulas,this paper makes analysis of bending resistance on the damaged beams under the coupling action of load and environment and the coupled damaged beams strengthened with CFRP.The main contents are as follows:(1)Through the pre loading and seawater dry wet cycle test of ordinary reinforced concrete beams,the mechanical damage and steel corrosion damage of the test beam is close to the actual structure.Through the measured data,the mechanical damage and steel corrosion damage are quantified,and the mechanical damage degree and steel corrosion rate are obtained.The coupling damage degree of each test beam is determined by analyzing the measured value and theoretical value of the ultimate bearing capacity of the coupling damage beam;(2)The flexural loading tests of the coupled damaged beams and the coupled damaged beams strengthened with CFRP are carried out.The results show that the yield strength,flexural bearing capacity and stiffness of the tested beams all decrease with the increase of the degree of coupling damage.(3)The deflection,steel strain,ultimate load,crack development and concrete strain of coupled damage beams strengthened with CFRP are compared with those of unreinforced coupled damage beams to study the effect of bonded CFRP on the degradation of flexural performance of coupled damage beams.The results show that: the stiffness,flexural capacity and yield load of coupled damaged beams strengthened with CFRP are improved;the crack width is reduced,but the number of cracks is increased;(4)Based on the theoretical formula of flexural bearing capacity of ordinary beam,the test data of corrosion damaged beam and coupling damaged beam are fitted,and the functional relationship between cooperative work coefficient and mechanical damage degree and steel corrosion rate is established,and the calculation formula of flexural bearing capacity of coupling damaged beam is derived.Based the experimental data on the theoretical formula of ordinary beam stiffness,combined with the load deflection test of coupling damaged beam in this paper,the relevant parameters are fitted and modified,and the stiffness calculation formula of the beam with load and environment coupling damage is derived.(5)Based on the mechanism of debonding failure at the middle bending crack,the calculation formula of debonding bearing capacity of ordinary beams strengthened with CFRP is derived.Through the analysis of the influence of mechanical damage,steel corrosion damage and other parameters on the interface bond stress,combined with the experimental data of coupled damage beams strengthened with CFRP,the calculation formula of debonding bearing capacity of coupled damage beams strengthened with CFRP is obtained.The c-spline equation is derived by using the stiffness analytical method Based on the experimental data of related scholars and this paper,the reduction formulas of mechanical damage and steel corrosion on relevant parameters are obtained,and the stiffness calculation formula of load and environment coupling damage beam strengthened by CFRP is derived.