箍筋弯曲部断裂分布对RC长梁受剪性能影响

Influence of bend fracture distribution of stirrup on shear behavior of slender RC beams

[目的]探究碱集料反应(AAR)导致的箍筋弯曲部断裂劣化对RC长梁抗剪性能的影响.[方法]采用人工方法模拟箍筋弯曲部断裂,通过三点加载调查试验梁宏观受剪性能,并在试验的基础上使用有限元软件Diana模拟试验梁的受剪承载行为.[结果]研究结果表明:相比完好梁,支点附近箍筋下端弯曲部断裂以及箍筋下端弯曲部全部断裂的缺陷梁的受剪承载力分别下降了10.0%和12.6%;仅加载点附近箍筋下端弯曲部断裂的缺陷梁下降了0.1%;支点附近箍筋下端和加载点附近箍筋上端弯曲部均断裂的缺陷梁则下降了18.6%.[结论]支点附近箍筋下端弯曲部断裂弱化了拱机制,降低了混凝土抗剪贡献;加载点附近箍筋上端弯曲部断裂降低了侧肢在与主斜裂缝相交位置的抗拉力,从而减弱了箍筋参与桁架机制的抗剪贡献,而下端弯曲部断裂对抗剪的影响并不明显;当支点附近箍筋下端弯曲部和加载点附近箍筋上端弯曲部同时断裂时,拱机制和桁架机制均受到削弱,承载力下降最为显著.

[Objective]Investigating the influence of alkali-aggregate reaction(AAR)induced fracture at bends of stirrups on the shear performance of reinforced concrete(RC)long beams.[Methods]This study used an artificial method to reproduce the fracture at the bend of stirrup,and investigated the shear behavior of such defected beams through three-point loading.In addition,this study also analytically investigated the shear performance of these test beams by a simulation study using a commercial finite element software Diana.[Results]The results indicated that compared to intact beams,the shear capacity of defective beams with the fracture at lower bends of the stirrup near the supports and complete fracture at lower bends of the stirrup decreased by 10%and 12.6%,respectively.Defective beams with the fracture only at the lower bends of the stirrup near the loading positions experienced a decrease of 0.1%.However,the defective beam,in which stirrups fractured at the bottom bends near the supports and the upper bend near the loading positons decreased by 18.6%.[Conclusions]The fracture at lower bends of the stirrup near the supports weakened the“arch action”and thus reduced the concrete contribution to the shear strength.The fracture at upper bends near the loading points reduced the tensile force of the cross point of stirrup side-legs with the critical shear cracks,and thus reduces the shear contribution from the stirrups through“truss action”,while in comparison,the fracture at lower bends of the stirrups near the loading positions has little impact.When the stirrups fractured at the bottom bends near the supports and the upper bend near the loading positons,both the“arch action”and“truss action”were weakened,and thus the shear capacity decreased most significantly.