Punching of reinforced concrete flat slabs with holes and shear reinforcement

Abstract Punching shear is a possible type of failure that occurs in reinforced concrete flat slabs, which can develop with an ultimate load below flexural capacity. Several researchers have studied the punching resistance of flat slabs over recent years. Although they have made great advances, there are codes that show different approaches to a singular design. Some codes show that there exist contradictions, even in the simplest situations, such as concentric loads. Most codes prescribe empirical expressions based in a theoretical model to analyze punching strength, but for flat slabs with holes around the column and shear reinforcement there are divergences between codes, justifying research in this area. This paper presents an experimental analysis of nine square reinforced concrete flat slabs under concentric loading (width: 1800 mm; thickness: 130 mm). The main variables used in the tests were: a) two square openings (150 mm) adjacent to the smallest side of the column and b) the use of shear reinforcement containing 3 layers, with 6 or 8 elements in each layer and radially distributed around the column. The research concludes that openings adjacent to the column affect punching shear strength, while the correct use of the shear reinforcement can minimize and even compensate this loss.

摘要：冲切剪切（punching shear）破坏是钢筋混凝土平板可能发生的破坏形式之一，其极限破坏荷载可低于受弯承载力。近年来，诸多学者围绕钢筋混凝土平板的冲切抗力开展了相关研究。尽管现有研究已取得显著进展，但不同设计规范针对同一设计场景采用了各异的处理方法，部分规范甚至在轴心荷载（concentric loading）作用这类简单场景下仍存在相互矛盾的规定。多数规范均采用基于理论模型的经验表达式来分析冲切强度，但针对柱周带有孔洞且配置抗剪钢筋（shear reinforcement）的平板，不同规范间仍存在较大分歧，这也为该领域的后续研究提供了充分必要性。本文对9块方形钢筋混凝土平板开展了轴心荷载作用下的试验分析（平板边长1800mm，厚度130mm）。本次试验设置的主要变量包括：a）在柱的最小侧边邻近位置设置两处150mm见方的开孔；b）采用三层抗剪钢筋，每层分别包含6根或8根沿柱周径向分布的抗剪连接件。研究结果表明，柱侧邻近开孔会降低平板的冲切剪切强度，而合理配置抗剪钢筋则可削弱甚至完全弥补该强度损失。