| The bond anchorage between steel bar and concrete is one of the basic mechanical properties of reinforced concrete structure,which has an important influence on the bearing capacity of reinforced concrete structure.Most of the existing studies are carried out under the condition of short anchoring length,focusing on the bond anchoring performance between steel bar and concrete before steel yielding.The research mainly obtains the average bond strength through the tests of different anchoring lengths,and then obtains the anchoring length of steel bar according to the average bond strength.However,under extreme load conditions,the steel bar stress exceeds its yield strength and enters the strengthening stage,and the steel bar yields and penetrates along the steel bar at both ends.The yield of steel bar will not only increase the relative slip between steel bar and concrete,but also decrease the local bond stress between steel bar and concrete.Therefore,in order to deeply study the bond anchorage performance of steel bar after yielding,15 beam end bond anchorage tests were designed and completed in this paper.By pasting strain gages along the anchorage length of steel bar to measure the strain distribution of steel bar.Taking the steel bar strength grade（HRB400,HRB500,HRB600）,concrete strength（C35,C45,C70）,steel bar diameter（16mm,20 mm,25mm）,relative protective layer thickness（1.5d,3d,4.5d）,stirp（C 6@60、C 6@100、C 6@200）and relative anchorage length（10d,15 d,20d,30 d,40d）as test variables,The relative slip at loading end,the strain distribution of steel bar,the stress distribution of steel bar,the bond stress distribution,the yield penetration depth and the average bond stress in the yield penetration section are studied and analyzed.Based on the test results,the formula for calculating the relative slip of the loading end after steel bar yielding is obtained by statistical regression.At the same time,a method for calculating the anchorage length after steel bar yielding is proposed,which can effectively calculate the anchorage length after steel bar yielding.In addition,based on the basic structural requirements of GB 50010-2010 and considering the diameter of steel bar and the strength of concrete and steel bar influence on the anchorage length,the ultimate anchorage length obtained by the design formula of GB50010-2010,ACI318-19,ACI Committee 408,EC2-2004 and fib Model Code 2010 were compared with the ultimate anchorage length obtained by the calculation method proposed in this paper.Based on this,the accuracy and safety of the ultimate anchorage length calculated by the design formula of GB50010-2010 are evaluated. |
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