Punching shear strength of waffle flat slabs

Abstract This research aimed to compare the ultimate load of 10 waffle flat slabs with different sizes of solid area and spacing between ribs. For this, a non-linear computational simulation of the slabs was carried out until their failure using the engineering software ANSYS. The failure modes and loads were analyzed, and the results showed that the models with less solid area presented less bearing capacity in comparison to the models with greater solid area when the failure mode was shearing of the ribs. The slabs with the largest solid regions experienced punching shear and behaved in a similar way as solid flat slabs, indicating compliance with the codes in relation to their punching shear strength provisions, especially with the NBR 6118. The results show that a square solid area whose length is 15% of the span is reasonable and that the ACI, Eurocode 2 and NBR 6118 provisions underestimate the shear strength of the ribs.

摘要 本研究旨在对比10个不同实心区域尺寸与肋间距的双向密肋平板楼盖的极限荷载。为此，本研究采用工程软件ANSYS对该类楼盖进行非线性数值模拟，直至其发生破坏。对破坏模式与极限荷载进行分析后结果表明：当破坏模式为肋体受剪时，实心区域尺寸较小的模型其承载能力低于实心区域尺寸更大的模型。实心区域最大的楼盖发生冲切破坏，其受力行为与实心无梁楼盖相近，表明其符合相关规范的冲切强度设计要求，尤其契合巴西混凝土结构设计规范NBR 6118的相关规定。研究结果显示，边长为跨度15%的方形实心区域设计方案较为合理；同时，美国混凝土学会（ACI）规范、欧洲规范2（Eurocode 2）及NBR 6118均低估了肋体的抗剪强度。