| Engineered cementitious composite(ECC)exhibits strain hardening and multiple cracking characteristics under tension.Under compression,it can retain residual strength and has a high level of damage tolerance.It is an ideal material to improve the inherent defects of ordinary concrete.Reinforced ECC beams can effectively improve structural durability and seismic performance,and have been gradually used in high-rise buildings and bridge projects in the United States,Japan and Europe.However,in actual projects,there is a lack of standardized design methods and test data support,and the bending performance of reinforced ECC beams may not be fully utilized,and even unexpected failure forms may occur.There are relatively few researches on the contribution of compressive zone properties of ECC beams to the bending performance of test beams at home and abroad.At the same time,the influence of tension stiffening effect of reinforcement on the bending performance of reinforced ECC beams has not yet formed a systematic theory and model.Therefore,further research on the flexural performance of reinforced ECC beams is of great theoretical and practical significance.Four-point bending tests were carried out on 7 test beams,including 6 PVA-ECC beams and 1 ordinary concrete comparison beam.Based on the test results,the bending performance of the comparison beams and PVA-ECC beams under different reinforcement ratios was discussed.By considering the tensile stiffness effect of the steel bar,the effective stiffness method is adopted to explore the deformation ability of the PVC-ECC beam before the main crack develops.Finally,based on the Diana finite element software,numerical simulation and parameter analysis of the test beam are carried out.The main conclusions are as follows:(1)With the increase of reinforcement ratio,the stiffness,ultimate bearing capacity and yield deformation of PVA-ECC beam increase,but the ductility increases first and then decreases within the range of test reinforcement(0.419%～1.675%).(2)The PVA-ECC beam has a strong damage tolerance in the compression zone,and does not collapse in a large area even if it reaches a large strain value.At the same time,with the reinforcement of the tensile zone,the properly reinforced PVA-ECC beam has high ductility and strong peak load maintenance capacity.(3)The effective stiffness method considering the effect of tension stiffness of the steel bars is used to theoretically calculate the short-term stiffness,curvature and deflection of the test beam before the main cracks are developed.The theoretical calculation results are in good agreement with the experimental results,but the theoretical calculation results are generally conservative.(4)Based on DIANA software,the finite element analysis of the test beam is carried out,and the influence of tensile rigidity of reinforcement is fully considered.The simulation results are in good agreement with the test results.Parameter analysis results show that the increase of reinforcement strength grade has little effect on the stiffness,but the ultimate bearing capacity of the test beam is effectively improved,and the appropriate reinforcement strength can obtain greater deformation capacity.When the reinforcement ratio ranges from 0.269% to 0.419%,increasing the longitudinal reinforcement ratio can effectively improve the bearing capacity and ductility. |
