Study On Flexural Behavior Of High-ductility Concrete Reinforced Damaged Concrete Beams Under Repeated Load

Nowadays,concrete structures can be found everywhere and have a profound impact on people’s lives.However,as concrete ages,a series of safety issues are gradually being taken into account,so concrete structure reinforcement and strengthening technology has emerged.High ductility concrete has high strength,high toughness,excellent tensile deformation properties and multiple crack development characteristics,the use of high ductility concrete for structural reinforcement is very promising.In this paper,a study of the flexural performance of damaged concrete beams without webs reinforced with high ductility concrete was carried out under repeated loads,and the main work done is as follows.(1)The preliminary tests focused on the effect of the thickness of the HDC reinforcement layer on the reinforcement effect of the damaged beam by cutting out the damaged part of the original beam and pouring the HDC reinforcement layer on on this basis.The test results show that the greater the thickness of the reinforcement,the higher the ultimate bearing capacity of the beam,and with the gradual increase of the thickness of the reinforcement,the more obvious the increase of the ultimate bearing capacity;while the residual deformation of the reinforced beam decreases to a certain extent with the increase of the thickness of the reinforcement.Compared to a reinforced beam with a reinforcement thickness of 0,the bearing capacity of reinforced beam with a reinforcement thickness of 10mm,15mm and 20mm can increase by 19.8%,32.7%and 46.3%,while the residual deformation decreases by 8.96%,13.3%and 20.47%respectively.(2)The effect of the longitudinal reinforcement/the thickness of HDC reinforcement layer and the hoop reinforcement/the thickness of HDC reinforcement layer on the reinforcement of the damaged beams was investigated in the later stage by reinforcing twelve beams by cutting out the damaged parts of the original beams,then placing longitudinal reinforcement at the bottom of some original beams and hoop reinforcement in the middle of the span of another part of the beams,finally pouring the HDC reinforcement layer.The test results show that the hoop reinforcement,the longitudinal reinforcement and the bottom HDC reinforcement layer can work together in a coordinated manner during the stressing process.In particular,the strain in the hoop reinforcement increases very slowly with increasing load.The load-strain curves of the longitudinal bars and HDC at the bottom of the beam show an approximately parallel trend,and the HDC reinforcement layer can automatically adjust the force distribution with the reinforcement during the stressing process,so that the uneven strain growth of the reinforcement and HDC reinforcement layer at the beginning gradually changes to a uniform strain growth.Compared to the beams before reinforcement,the bearing capacity of the test beams increased significantly after reinforcement tying and HDC pouring,in which the bearing capacity of the tied longitudinal reinforcement series increased the most,with a maximum increase of 86.2%after reinforcement;the bearing capacity of the tied hoop series increased by 33.3%after reinforcement;the bearing capacity of the unreinforced series increased by 16%after reinforcement.The cracking load of the reinforced beams did not change significantly due to the change in reinforcement method,but the cracking load of all types of reinforced beams was higher than that of the original beams after reinforcement.Compared to the original beams,the cracking load can be increased by up to 150%and by as little as 2.8%.(3)In the previous experiment,the stress reduction coefficient α and height reduction coefficient β were derived directly from the Principles of Structural Design of Concrete by equating the curved stress pattern in the compression zone to a rectangular stress pattern.In the later test,the stress reduction coefficient α and height reduction coefficient β are deduced by actual failure mode of reinforced beam,and the calculation formula of flexural bearing capacity of reinforced beam is derived,the test value is in good agreement with the calculated value.(4)On the basis of ultrasonic detection of reinforced beams before and after loading,a method for determining the internal defect points of beams based on relevant acoustic parameters is concluded using the probabilistic judgment method,and the calculation results are in good agreement with the automatic determination results of the instrument;and a damage model using ultrasonic sound velocity values to indicate the degree of damage of test beams at different stages was derived,and the calculation results of this model can better describe the crack generation of different types of beams.