Effects of impact loads on heated-and-cooled reinforced concrete slabs

The potential collapse of heavy components in fires can cause dynamic loads on slabs triggering a progressive collapse of weakened slabs on lower floors. In this study, three reinforced concrete (RC) slabs heated under ISO-834 standard fire for 30, 45, and 60 min, while one slab used as a control specimen. The effects of impact loads due to the falling weight were studied using the low-velocity impact test on RC slabs. The acceleration of midspans is recorded, and the dominant frequency and crack pattern of the specimens are measured. The experimental results used to verify the finite element (FE) models. A set of parametric studies are conducted to evaluate the peak acceleration, maximum and residual displacement, load, stiffness, and absorbed energy of heated RC slabs. The outcomes of the parametric study are fed into a machine learning model called Multilayer perceptron (MLP). Results showed that the fire duration affects and reduces the peak acceleration and frequency of the slabs. The average reduction for peak acceleration was 23% for all tested slabs. Numerical results revealed that the impact load with a low energy (i.e., low mass and the height of drop) has a weak dependency on the time of exposure and reinforcement ratio. The results of this paper impact the fire safety design of the RC slabs and the evaluations of fire-exposed RC slabs.