Study on bond-anchorage performance of steel bar after yielding based on splitting failure of protective layer
Code for design of concrete structures(GB 50010-2010)requires that the tensile failure of steel bars precedes the anchorage failure,but under the action of earthquake,the structure often suffers from anchorage failure.In addition,Code for design of concrete structures(GB 50011-2010)requires that the strength-yield ratio of seismic steel bars should not be less than 1.25,but the correction coefficient of seismic anchorage length only considers the adverse effect of reciprocating load on the bonding performance of steel bars,and does not explicitly require the additional anchorage length required for steel bar stress to reach 1.25fy.The bond-anchorage performance of steel bar after yielding under the condition of splitting failure of concrete protective layer was discussed mainly through experimental research method.The strain distribution of the steel bar was measured by slotting on the surface of the steel bar and pasting the strain gauges.The anchorage test of 21 beam-end specimens was completed with the variables of concrete strength,steel bar strength,steel bar diameter and protective layer thickness.The results show that after the steel bar yields,the slip at the loading end increases significantly,and the bond stress at the yield section decreases.The occurrence of splitting cracks will lead to the redistribution of bond stress,which is transformed from the problem of anchorage at the end of steel bar to the problem of bond-anchorage between cracks.Based on the test results,the formula for calculating the anchorage strength after the yield of the steel bar and the constitutive model of the stress-slip of the steel bar were obtained,which can better predict the anchorage bearing capacity of the steel bar and the slip of the loading end.
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