Experimental Study On Bond Performance And Anchorage Length Of ECC And Ordinary Steel Bars

Engineered Cementitious Composite(ECC)is one of the most popular concrete in recent years.Because of its strain hardening characteristics,multi joint cracking characteristics and so on,many countries have done a lot of research on it,and some properties of ECC have been gradually improved.In this paper,a series of researches on the bond performance between steel bars and ECC are carried out by pull-out test,and the stress of steel bars under different pull-out forces is tested by the method of sticking strain gauge on the surface of steel bars,the bond slip relationship under different anchorage positions is established,the critical anchorage length is analyzed and so that ECC can be applied in practical engineering more reasonably.The main conclusions are as follows:1.The ultimate tensile strain of ECC is more than 3%,its strain hardening phenomenon is obvious,and it has the characteristics of multiple cracks.The design tensile strength of ECC is calculated.2.In general,the bond slip curve of steel and ECC is analyzed in several stages: Micro slip stage,slip stage,pull-out stage,descent stage and residual stage.3.Taking the thickness of protective layer,anchorage length,diameter and type of reinforcement and concrete type as test parameters,this paper analyzes their influence on bond performance,and establishes a statistical formula of ultimate bond strength.Through analysis,it shows that the bond strength calculated by the formula is compared with the real bond strength of test results,and the fitting effect is good.4.The stress of the steel bar in the anchorage length of the test piece is obtained through the test of the steel bar's external surface mounting,and then the corresponding bond stress is deduced by the relevant formula,and the relationship between the relative slip and the anchorage position is obtained through calculation,finally the anchorage position function of different concrete is obtained,and the real meaning is establi shed based on the average bond slip formula The constitutive relation provides a theoretical basis for the finite element analysis.5.Based on the experimental bond anchorage relationship and the statistical formula of ultimate bond strength,the reliabi lity analysis of anchorage between reinforcement and ECC is carried out.The results show that the critical anchorage length calculated according to the code for design of concrete structures is more conservative.