Experimental Study On Impact Resistance Of CFRP Repaired Reinforced Concrete Composite Beams

In recent years,the renovation and re-use of building structures has gradually become a new direction for the development of the domestic construction industry.As a horizontal force member commonly used in prefabricated buildings,the research on the dynamic performance of the restored reinforced concrete composite beams under impact load is one of the important topics in the field of civil engineering disaster prevention and reduction.And as the main object of the research,this paper studies the bending and impact resistance of CFRP repaired reinforced concrete composite beams by experiments,simplified calculations and finite element simulation.The main research work is as follows:(1)The bending performance test of one ordinary reinforced concrete cast-in-situ beam and three reinforced concrete composite beams with different shape stirrups was carried out.During the test,the bearing capacity,deflection,concrete and steel bar strain of the test piece were measured,and the variation of the crack of the laminated beam with the load and the difference of the failure modes of each test piece were expounded.The influence of the stirrup form on the mechanical behavior of the composite beam and the applicability of the U-shaped stirrup in the composite beam is also discussed,which lays a foundation for further study of the bending resistance of damaged composite beams after repair.(2)Four cast-in-place/composite beams with intact and damage repair were tested.The fracture morphology,stiffness,deflection and bearing capacity of the repaired beam under bending load were obtained.The improvement effect of CFRP repair on the flexural behavior of laminated beams and the similarities and differences between the cast-in-situ beams and the composite beams are analyzed.The simplified calculation of the bearing capacity of a damage repaired beam based on the experimental results and the theoretical research basis is in good agreement with the experimental results.(3)Through the drop hammer tester designed by ourselves,four impact tests of cast-inplace/laminated beams with intact and damaged repairs were carried out.The dynamic response such as load peak,deflection,crack distribution and strain change of the specimen was obtained.The change of impact resistance of the repaired beam relative to the intact beam on various response parameters and the difference of the dynamic performance between the composite beam and the cast-in-situ beam under impact load is described.The improvement of the impact resistance of the laminated beam after repair is analyzed.(4)The drop hammer impact model of reinforced concrete beams was established by using finite element analysis software ANSYS/LS-DYNA.The simulation variables were simplified and more impact conditions were set to analyze the influence of CFRP on the dynamic performance of RC beams under impact.The difference between the theoretical resistance contribution of CFRP to the damaged beam and the actual resistance contribution was discussed by combining the damage beam results of the test,and the causes of the difference were also analyzed.The results of simulation and analysis provide a reference for the design method of fiber composite repair beam and the further study of the impact resistance of FRP.