Experimental Study On Anchorage Performance Of 90° Hooked Bar

The 90° hooked bars（hereinafter referred to as hooked bars）is a common mechanical anchorage method,which is widely used in the beam-column joint of reinforced concrete frame to solve the development length design problem that the height of column section is not enough to provide enough development length of straight reinforcement to make the reinforcement reach its design strength.In order to study the magnitude and proportion of anchorage capacity of each part of hooked bars,PVC casing were placed in each anchorage section of the hooked bar to eliminate the adhesion between the reinforcement and concrete,and the purpose of separating the anchorage capacity was achieved through mutual comparison tests.This study used HRB500 grade reinforcement as the hooked bar,and completed 9 sets of mutual comparison tests with its horizontal projection length,bending radius,vertical projection length and hoop spacing as variables,and a total of 36 anchorage performance tests of hooked bars in the beam-column joint of reinforced concrete frame intermediate floors.In this paper,the hooked bar is equated to straight reinforcement and based on the test results of this study,a calculation model of anchorage strength of hooked bars is proposed,and the calculation results are in good agreement with the test values of this paper,and the increment of anchorage strength per unit anchorage length of each anchorage section is analyzed according to the calculation formula.ACI318-19,EC2-02,fib MC2010,GB50010-2010 and this paper fitted regression formula for error analysis,and the fitted regression formula for the lower limit of bias to obtain the proposed formula for calculating the anchorage strength of hooked bar;the calculation results of anchorage length and this paper proposed formula for comparison analysis of national codes.This study results show that: the placement of PVC casing has a significant effect on the crack development process and the damage pattern of the specimens;when the anchorage damage occurs,the compression force of the concrete on the bending reinforcement accounts for the major part of the total anchorage bearing capacity,and its proportional distribution ranges from 27% to 48%,and increases with the decrease of the hoop spacing;the anchorage capacity provided by the horizontal anchorage section accounts for 18% to 34% of the total anchorage capacity,and its proportional distribution increases with the decrease of the horizontal projection length.The anchorage capacity provided by the horizontal anchorage section accounts for 18%～34%of the total anchorage capacity,and its proportion increases with the increase of the horizontal projection length;the anchorage capacity provided by the bending arc anchorage section accounts for 12%～34% of the total anchorage capacity,and increases with the increase of the horizontal projection length and the bending arc radius;the anchorage capacity provided by the vertical anchorage section accounts for 11%～23%of the total anchorage capacity,and shows a decreasing trend with the increase of the hoop spacing and the decrease of the vertical projection length,and accounts for the least in each part of the anchorage capacity.The anchorage capacity of bending bars accounts for 11%～23% of the total anchorage capacity,and decreases with the increase of hoop spacing and vertical projection length.The calculation results show that: increasing the radius of bend,horizontal projection length and vertical projection length can improve the anchorage strength of hooked bars,and their influence degree decreases,and the influence degree of the first two is much higher than the influence degree of changing the vertical projection length;the relevant provisions of GB50010-2010 have certain safety risks,and the proposed formula is moderately safe and discrete than the specification of each country;China’s specification calculation results are not safe,this paper suggests that the formula calculation results in a reasonable range.