Effect of asymmetric flexural reinforcement ratios on punching shear resistance

The impact of varying flexural reinforcement ratios in the orthogonal directions (ρx and ρy) on the punching shear resistance (PSR) of flat slabs was experimentally investigated. Six slabs, measuring 1.5 m × 1.5 m × 0.15 m, were tested, with a constant average reinforcement ratio (ρav) of 0.3% and ρx/ρy ratios ranging from 1.2 to 3.0. The results indicated an insignificant effect on punching resistance for ρx/ρy ≤ 2.5. Increasing ρx/ρy led to wider, more dispersed cracks and enhanced ductility. Comparisons of various codes (BS 8110-1:1997, ACI 318-19, the first and second generations of Eurocode 2 (EC2-2004 and EC2-2023, respectively) and fib Model Code 2010 (MC2010)) revealed that BS 8110-1:1997 provided conservative predictions except for ρx/ρy = 3.0, while ACI 318-19 consistently overestimated the punching resistance. MC2010 (level of approximation IV) accounted for the reduction in PSR at higher ρx/ρy ratios. Tests from the literature with ρx/ρy up to 4.4 exhibited further strength reduction. Comparisons of EC2-2004 and EC2-2023 showed that EC2-2004 gave conservative estimates, with diminishing accuracy as ρx/ρy increased, while EC2-2023 accurately predicted the punching resistance for ρx/ρy ≤ 2.5, but overestimated it for higher ratios. This study highlights the limitations of current codes in addressing reinforcement asymmetry effects, and recommends incorporating a reduction factor in EC2-2023 for ρx/ρy > 2.5 to account for reduced PSR.