Study On Cracking Resistances Of Prestressed Beams With Hybrid Steel Fiber Reinforced High Strength Recycled Concrete

In order to improve the crack resistance of hybrid steel fiber high strength recycled concrete（HSFRHSRC）flexural members,this paper conducts basic mechanical performance tests on HSFRHSRC test blocks,analyze the effect of the volume mixing rate of hybrid steel fiber（HSFR）on the mechanical properties of high strength recycled concrete（HSRC）.Through the normal section bending performance test of HSRC prestressed beams,the effects of HSFR fiber content,tensile control stress σcon and ordinary longitudinal reinforcement ratio on the crack resistance and ductility of the beam are studied.The main research results of this article are as follows:（1）The blending of HSFR has a good effect on improving the brittleness of HSRC and improving its crack resistance.The effect of the fiber increases first and then decreases with the increase of the blending rate.Comprehensively considering the basic mechanical properties of HSFRHSRC studied in the experiment,when the volume blending rate of HSFR is 1.2%,the mechanical properties of the test block are excellent:the compressive strength is increased by 15.7%,The split tensile strength is increased by 101.2%.（2）For the cracking load of the test beam,prestress plays the most important role.The larger the σcon,the greater the cracking load（increased by 37.5%）,followed by the influence of fiber incorporation（increased by 23.3%）,and the ratio of ordinary longitudinal reinforcement has the least influence on the cracking load.For yield and ultimate load,HSFR blending rate has the greatest impact,the yield strength increase is as high as 37.5%,the ultimate load is increased by 50%,the ordinary longitudinal reinforcement ratio is second,and the yield load increases by 25%as the ratio of longitudinal reinforcement increases.Analyzing the crack morphology,width,number and average crack spacing of the test beam,it can be seen that the incorporation of HSFR has a better effect on improving the crack morphology.Compared with the S0-R14-0.65 group,the maximum crack width of S1.2-R14-0.65 group decreased by 28.9%,the number of cracks increased by 36.4%,and the average crack spacing decreased by 22.7%;the increase of the tension bar ratio is also beneficial to the development of crack morphology.Compared with the S0.8-R12-0.65 group,the maximum crack width of the S0.8-R16-0.65 group is reduced by 16.5%,and the average crack spacing is reduced by 20.3%.（3）The ductility first increased and then decreased with the increase of HSFR blending rate.Among them,the S1.2-R 14-0.65 group increased by 94%compared with the S0-R14-0.65 group,while the S1.6-R14-The 0.65 group is only 6.8%higher than the S0-R14-0.65 group;the higher the tension control stress σcon,the worse the ductility of the beam（the displacement ductility coefficient is reduced by 46.8%）;the increase in the longitudinal reinforcement ratio can be slightly improved（increased 12.7%）displacement ductility coefficient.（4）On the basis of the existing research literature and standard research results,through the fitting analysis of the key influence coefficient,the calculation formulas of the cracking moment and the maximum crack width of the HSFRHSRC prestressed beam are obtained.（5）Using ANSYS APDL finite element to simulate the bending failure test of HSFRHSRC prestressed beams,the results are basically consistent with the test results,and the simulation effect is good.