Experimental Study On Anchoring Performance Of Steel Bars And Concrete Under Catenary Effect

The bond failure between steel bars and concrete under the catenary action was studied.whether steel bars or bond are the earliest failure was investigated in the progressive collapse process of RC frame structure.the effects of changing anchor length and the arrangements of reinforcement on the bond-anchorage performance were studied.It is significant for evaluating anti-collapse capacity of RC frame structure.The main contents of this paper are as follows:(1)The steel bars were anchored in reinforced concrete column.The steel bars were anchored in reinforced concrete column,and the steel bars formed the mechanical mechanism of catenary which occurred when the end of beam in RC fame structure was damaged but the steel bars was not broken.The process of adding load to the steel bars was achieved by the selfbalancing reaction frame.The test results show that the splitting failure of bond has been seen,while the stress of steel bars doesn't reach the ultimate tensile strength.It is suggested that according to the experimental results,the direct-anchorage form should not be used in the collapse-resistant design of RC frame structures,and other more effective anchorage form should be adopted in the future.(2)The direct-anchorage form trends to improve the average bond stress under the single row reinforcement arrangement.Compared with the average bond stress under the double reinforcement arrangement,the average bond stress can be increased by 15%.Based on the previous researches on the bond-slip constitutive relation and the experimental date in the paper,this paper proposed the mathematical model of the bond-slip constitutive relation under the catenary action and the fitting formula expression of the bond strength.Furthermore,the effects of increasing the anchor lengths and the arrangement of reinforcement on the bond strength and the values of exponential coefficient of the expression in the bond-slip constitutive relation were analyzed.(3)The distributed rule of local bond stress in the grooved steel bars from the load-end to the free-end was analyzed.The maximum local bond stress distribution,according to the result of the analysis,trend to develop towards the free-end with the increase of the number of steel bars,and it is not related to the reinforcement arrangement.