Probabilistic assessment of ACI 318 minimum thickness requirements for two-way slabs

ABSTRACT Following the ACI 318 design code and to control deflections, structural engineers must adhere to minimum thickness requirements for reinforced concrete (RC) slabs. However, these requirements do not account for various influencing variables such as span length, aspect ratio and applied live load. This paper assesses the adequacy of the ACI 318 minimum thickness requirements for two-way RC slabs through a probabilistic approach using Monte Carlo simulation (MCS). The probability distribution of the span-to-depth ratio (SDR) was fitted to the Burr distribution, and the goodness-of-fit test was applied to assess the fitting. Then, the effect of span length, aspect ratio, and live load on the maximum allowable SDR was evaluated, considering all material properties and applied loads as random variables. The analyses have shown a high correlation between the studied variables and the SDR. Therefore, multiple regression analysis was carried out, and four prediction models were proposed to conservatively predict the SDR for two-way slabs. The accuracy of the prediction models was statistically tested by comparing calculated to predicted SDR values, and a 10% maximum relative error was exhibited. The proposed prediction models were accurate for all practical ranges of span length, aspect ratio and live load in two-way slabs.