混凝土梁教学实验中的异常开裂机理探讨

Study of abnormal cracking mechanism of RC beams in the teaching experiment

针对钢筋混凝土简支梁剪压破坏性教学实验,在加载临近极限承载力时,梁端上部受压混凝土出现竖向开裂的异常现象,认定混凝土受压区出现拉应力;通过剪跨段上部混凝土应变测试,得到随荷载增加应变由压变拉的试验数据;根据实测应变分布,计算钢筋与混凝土在完全锚固情况下的粘结剪力,并与混凝土对钢筋的实际粘结强度进行比较,得出钢筋与混凝土粘结破坏并产生滑移的结论;认为剪跨段短,上部纵向应变梯度大,滑移引起的钢筋相对伸长在混凝土中产生拉伸效应,是导致剪跨段上部混凝土竖向开裂的主要原因,并提出验证实验方案。

The destructive teaching experiment on the reinforced concrete simple beam is discussed. When loading approached the ultimate carrying capacity, the abnormal cracking phenomenon appeared in the compression area of the beam top, and it is thought that tension appears in the compression area of the concrete. The experimental data of strain when compressive stress became tensile stress with the increase of loading were obtained by testing the concrete strain on the top section of the shear span. By testing strain distribution and calculating bond shear with complete anchorage between steel and concrete and by comparing the bond shear with the actual bond strength, it is concluded that bond failure and slip take place between steel and concrete. When the section of the shear span becomes shorter and the longitudinal strain gradient becomes longer, the effect of extension which is produced by the steel relative elongation due to the slip is the main reason that makes the top section of shear span concrete produce vertical cracks. The verification experiment schemes are also presented.