矩形开孔钢筋混凝土伸臂梁受剪性能试验研究

为方便设备管线通过，采用腹部开孔梁可有效降低楼层高度，但开孔会削弱梁的整体刚度，导致孔洞附近的应力及内力重分布十分复杂。为研究腹部矩形开孔的钢筋混凝土伸臂梁的受力性能，以正反弯矩比、孔洞位置、剪跨比及孔侧斜筋作为主要变量，对12根钢筋混凝土开孔伸臂梁和1根钢筋混凝土实腹伸臂梁试件进行了两点加载下的受剪性能试验。研究了各种参数对开孔伸臂梁的裂缝开展及破坏形态、应变分布、变形和受剪承载力等受力性能的影响。试验结果表明：正反弯矩比和孔心剪跨比改变了伸臂梁在孔洞附近的受力状态，导致破坏时孔侧呈现出不同的裂缝形态。配置孔侧斜筋后，孔侧混凝土和箍筋更好地发挥协同抗剪作用，试件的受剪承载力显著提高，裂缝开展和变形均得到有效的控制。利用混凝土开孔简支梁发生孔侧剪压破坏的受剪承载力公式对开孔伸臂梁的受剪承载力进行计算，并和试验数据进行对比可知，按开孔简支梁的算式对开孔伸臂梁的受剪承载力进行计算，计算结果与试验结果的平均比值为0.96，方差为0.07，结果偏于安全。

Experimental study on overhanging reinforced concrete beams with rectangular web openings

In order to facilitate the pipeline passage, reinforced concrete (RC) beams with openings can effectively reduce the story height, but the openings weaken the overall stiffness of the beams, resulting in complex redistribution of stresses and internal forces nearby. In order to study the mechanical properties of overhanging RC beam with openings, the ratio of positive and negative moments, position of opening, shear span ratio and strengthening diagonal reinforcement were designed as the main variables. The shear tests of 12 RC overhanging beams with opening and one solid-web RC overhanging beam were conducted. Based on the experimental results, the crack pattern, failure mode, strain, deflection and shear capacity were discussed. It can be observed that the ratio of positive and negative bending moments and position of opening significantly affect the structural behavior near the web openings, leading to different cracking propagation patterns at the ultimate stage. With strengthening diagonal reinforcement on both sides of web openings, the synergistic action by concrete and stirrups can be enhanced greatly, which leads to effective control of crack development and deformation. Furthermore, the calculation formulae of shear capacity of simply supported RC beams containing opening when the compression shear failure occurs at both sides of openings was used to calculate the shear strength of overhanging RC beams with web openings. A comparison between the calculated and experimental results indicates that the calculation formulae can safely predict the shear strength of overhanging RC beams with web openings. The average ratio of the theoretical results and the experimental results is 0.96, while the variance is 0.07.