Experimental Study On Bond And Anchorage Behavior Of New High Strength Reinforcement Bar And Concrete

630MPa grade heat treated ribbed high strength steel bar is a new type of steel bar.Compared with ordinary steel bar,it has the advantages of high strength,energy saving,environmental protection and excellent comprehensive performance.The bond and anchorage performance of 630 MPa grade steel bar and concrete is the key problem to popularize this kind of steel bar in engineering.In order to study the bond and anchorage properties of 630 MPa heat treated ribbed high strength steel bars and concrete,400 MPa grade steel bars and630 MPa grade steel bars are selected to make bond specimens between steel bars and concrete.The bond mechanism,main factors affecting bond properties,average bond-slip curve and anchorage length of ordinary steel bars and concrete specimens are tested by pull test method.The bond and anchorage properties of high strength steel bar and concrete are compared and analyzed.The effects of concrete strength,diameter of steel bar,thickness of protective layer,anchorage length and reinforcement ratio on bond and anchorage properties of 400 MPa and630 MPa high strength steel bars with concrete are studied.The variation rules of bond-slip curves of various specimens are compared and analyzed.The results show that the influence of various factors on the bond and anchorage properties of ordinary and high-strength steel bars and concrete is the same.The bond strength increases with the increase of tensile strength of concrete and increases first and then decreases with the increase of diameter of steel bars.Within the critical protective layer thickness range,the greater the relative protective layer thickness is,the greater the ultimate bond strength is;the longer the anchorage length is,the smaller the average bond strength is.The shape and trend of bond-slip curves of 630 MPa grade heat treated ribbed bar,HRB400 and concrete are basically the same.They can be divided into five stages: micro-slip stage,slip stage,splitting stage,descending stage and residual stage.Based on the statistical analysis of the tensile test results,a formula for calculating the bond strength of 630 MPa high-strength steel bars is proposed.The reliability analysis is carried out by the first-order second-moment method(central point method),and the recommended anchorage length design values of 630 MPa high-strength steel bars andconcrete are given.The results show that the design anchorage length of 630 MPa high strength steel bar can still be calculated according to the current Code for Design of Concrete Structures(GB50010-2010).