Study On The Flexural Performance Of Reinforced Concrete Beams Equipped With 635 MPa High-strength Reinforcement

Lightweight and high strength is the future direction of civil engineering materials development.By increasing the strength of reinforcement to reduce the amount of steel used,it is of great significance to improve resource utilisation.At present,there are relatively few studies on the performance of concrete members using high-strength reinforcement over 600 MPa,and there are still lack of experimental researches to verify the influence of various design parameters on the stress performance of beams with high-strength reinforcement over 600 MPa,as well as the applicability of the existing methods for calculating load carrying capacity and crack width.In order to promote the application of this type of high-strength reinforcement in practical projects,a systematic study of the flexural performance of concrete beams configured with 635 MPa high-strength reinforcement has been carried out in this paper,and the main contents and results of the study are as follows.(1)Firstly,11 ordinary concrete beams equipped with 635 MPa high-strength reinforcement and 6 fibre concrete beams equipped with 635 MPa high-strength reinforcement were tested for flexural performance.The parameters studied include reinforcement ratio,reinforcement diameter,concrete strength class and steel fibre admixture.The cracking and damage processes of the specimens were investigated,and the effects of these parameters on the load carrying capacity,stiffness and deformation capacity of the beams were analysed.The crack widths of the specimens were assessed under normal service conditions,and the applicability of the current concrete code formulae for calculating the cracking load and ultimate load carrying capacity of reinforced concrete flexural members to the high-strength reinforced concrete beams tested was checked.The results mainly show that the damage mode of the concrete beams with 635 MPa high-strength reinforcement is the same as that of ordinary reinforced concrete beams,which is controlled by the yielding of the tensile longitudinal bars and the crushing of the concrete in the compression zone,and that the increase in the reinforcement ratio and the amount of steel fibres can increase the load carrying capacity of the beams and can effectively control the crack width.(2)Based on the test results,the theories and calculation methods of crack widths in the Chinese,American and European codes are compared and analysed in depth,and the tested and calculated crack widths are compared.Meanwhile,the crack width data of the test beams measured in this test and some of the collected literature data were combined to make corrections to the formulae for the average crack spacing and maximum crack width in the current Chinese code.The results of the study mainly show that the calculation results based on the Eurocode formulae are in good agreement with the crack widths of the test beams,and the modified formulae can better predict the average crack spacing and maximum crack widths of this type of high-strength reinforced concrete beams.(3)A three-dimensional analysis model was established using the general finite element software ABAQUS for the tested concrete beams with 635 MPa grade high-strength reinforcement,and the whole process of stressing the specimens was numerically simulated by introducing suitable instantonal relationships between the reinforcement and the concrete.The moment-deflection curves,concrete strains and reinforcement stresses obtained from the analysis were also compared with the experimental results.The results mainly show that the moment-deflection curves and strain results obtained from the finite element analysis are in good agreement with the test curves and damage modes respectively,and that the finite element model can simulate the flexural performance of concrete beams with 635 MPa grade high-strength reinforcement relatively well,which can be used as the basis for the further study.