反复荷载作用下含缺陷灌浆套筒约束应力及钢筋黏结强度的预测模型

Prediction model for restraint stress and reinforcement bond strength of grouted sleeves with defects under cycling loading

为建立地震反复荷载作用下含缺陷灌浆套筒内部灌浆料与钢筋之间黏结强度的预测模型,对套筒的约束体系进行了分析,并根据缺陷的影响机理对缺陷进行了分类;设计了含缺陷的灌浆套筒试件并对其进行了低周反复加载试验研究,得到了含缺陷灌浆套筒约束应力的数学表达式,结合数学表达式建立了含缺陷灌浆料极限黏结强度的预测模型,通过与试验结果对比验证了预测模型的正确性。结果表明:缺陷导致的套筒约束体系失衡是造成套筒黏结性能劣化的重要原因,集中于一侧的缺陷会诱发套筒约束体系的失衡,因此对黏结性能的劣化影响相较于均匀分散的缺陷而言更为显著;随着缺陷率的增大,试件的失效模式从钢筋拉断向钢筋拔出转变;当含缺陷套筒的约束体系基本平衡时,出现钢筋拔出破坏的界限缺陷率约为30%;当缺陷导致套筒约束体系严重失衡时,出现钢筋拔出破坏的界限缺陷率仅为20%;灌浆端是套筒约束作用率先失效的薄弱部位,因此相较机械端出现的缺陷而言,在灌浆端出现的缺陷更容易诱发连接失效;该预测模型可为含缺陷灌浆套筒在地震区的性能评估提供理论参考依据。

In order to establish a prediction model for the bond strength between grout and rebar in grouted sleeves with defects under cycling seismic loading,the restraint system of the sleeve was analyzed,and the defects were classified according to the influence mechanism on the restraint system.The grouted sleeve specimens with defects were designed and investigated under cycling loading tests.The mathematical expression of the restraint stress of the grouted sleeve with defects was obtained.The prediction model of the ultimate bond strength of grout with defects was established by combining the mathematical expressions,and the correctness of the prediction model was verified by comparing with the test results.The results show that the imbalance of the sleeve restraint system caused by defects is an important cause of the deterioration of the sleeve bond performance.The defects concentrated on one side induce an imbalance of the sleeve restraint system,and therefore have a more significant effect on the deterioration of the bond performance than uniformly dispersed defects.As the defect rate increases,the failure mode of the specimen changes from reinforcement fracture failure to reinforcement pullout failure.When the restraint system of the defective sleeve is in equilibrium,the threshold defect rate for rebar pullout failure is approximately 30%.When the defect causes a severe imbalance in the sleeve restraint system,the threshold defect rate for rebar pullout failure is only 20%.The grouted end is the weak point where the sleeve restraint is the first to fail,so defects at the grouted end are more likely to induce connection failure than defects at the mechanical end.The prediction model can provide a theoretical reference for the performance evaluation of grout sleeve with defects in seismic zone.