受压区局部增强的钢筋混凝土梁抗剪性能

Shear behavior of reinforced concrete beam with local enhancement in compression zone

钢筋混凝土梁受压区的应力状态和材料性能对抗剪承载力和变形能力的影响显著.用性能更好的纤维增强水泥基复合材料(engineered cementitious composite,ECC)替换受压区混凝土,以增强钢筋混凝土梁的抗剪性能,是一个崭新的尝试.设计了4条全尺寸的钢筋混凝土梁,研究受压区ECC对有/无箍筋梁抗剪性能的影响;为得到准确的箍筋和混凝土的抗剪贡献,在箍筋内部安装应变片还原真实的箍筋抗剪贡献;为了解耦弯曲挠度和剪切挠度,采用非接触式数字图像系统测量混凝土表面的应变场.结果表明:受压区ECC改变了梁的破坏过程;对于无箍筋梁,受压区ECC的存在使得构件抗剪承载力和挠度分别提高了92.0%和97.3%,对于有箍筋梁,抗剪承载力和挠度提高幅度分别为5.2%和26.8%;在主斜裂缝发展过程中,普通混凝土梁的混凝土抗剪贡献缓慢下降,而受压区用ECC替换的梁则是先缓慢减小然后逐渐增大直至剪切破坏;用两种方法解耦了梁的弯曲挠度和剪切挠度,二者结果吻合较好;现有典型规范不能准确的预测混凝土与箍筋的抗剪贡献.

The stress conditions and material properties of the compression zone of reinforced concrete(RC)beam significantly influence the shear behavior.Using the highperformance engineered cementitious composite(ECC)to locally replace the compression zone concrete is a new pilot standpoint to enhance the shear performance of RC beams.Four full-scale RC beams are designed to investigate the effects of compression zone ECC on the shear behaviors of RC beams without and with stirrups.To accurately and directly obtain the shear contributions of stirrups and concrete,large numbers of strain gauges are installed inside each stirrup,rather than on the surface,aiming to eliminate the strain measurement error caused by the bond-slip effect.Digital image correlation(DIC)is adopted to monitor the strain fields of a concrete beam,based on which the flexural and shear deflections can be decoupled.The results indicate that the ECC changes the failure process of EC beams.For RC beams without stirrups,the inclusion of ECC increases the shear strength and deflection by 92.0%and 97.3%,respectively,and these two values are 5.2%and 26.8%for beams with stirrups.For beams with stirrups,from the occurrence of the critical diagonal crack to shear failure,the contribution of concrete of conventional RC beam decreases monotonically.However,for the beam with ECC,this component decreases first and increases again.Two methods are utilized to decouple the flexural and shear deflections,and the results matches well with each other.Some existing typical design codes cannot accurately predict the contribution of concrete and stirrups.