Abstract
Flat slab concrete buildings are widely found in infrastructure such as office and residential buildings or industrial facilities. The susceptibility of progressive collapse of such structures due to accidental loads is highly dependent on the structural performance of the slab-column connections. This paper presents a framework for a simplified reliability analysis and derivation of safety factors for computing the probability of punching of flat slab concrete buildings subjected to accidental loads such as column removal, slab falling from above or blast load. The main advantage of the proposed approach is that it considers in a simple manner, the uncertainty in the gravity load applied in the slab before the accidental event, which affects the inertial effects and demand/capacity ratio in the slab-column connections. Eurocode 2 and the Critical Shear Crack Theory for punching are used and extended to dynamic cases for the assessment of the demand/capacity ratio using computer-based time history finite element simulations. The proposed reliability method is applied to a case study of an existing building showing that the column removal situation is not always critical whereas the slab falling from above is much more detrimental.
Highlights
The main concern with flat slabs is that unless special measures are adopted, the shear capacity at the column-slab connection is low after punching failure which can contribute to a horizontal propagation of failure and subsequently the slab can fall onto the lower floor [1]
An increase in moment transfer will result in a higher concentration of shear forces in certain segments of the control perimeter adopted in the punching shear calculations which in turn results in a higher shear demand
Where KP0 is the standard normal variate to non-exceeding a probability of (1 À P0) which is obtained as KP0 1⁄4 UÀ1ð1 À P0Þ and rT is the qtoffiffiffitffiffiaffiffilffiffiffiffiffiffiffiffiffisffiffitffiffiaffiffinffiffiffidffiffiffiaffiffirffiffidffiffiffiffiffiffiffiffiffiffidffiffiffieffiffiviation, which is obtained as rT 1⁄4 r2C þ r2D À 2qCDrC rD; where lC and lD are the mean values of the punching shear capacity and demand respectively
Summary
Concrete flat slab structures is a common form of structural reinforced concrete (RC) construction in buildings, especially in medium-rise offices due to their efficient span/depth ratios and the economies gained by reducing the storey heights. Structural failures of flat slab buildings due to punching have been reported in the past in America, Asia and Europe; some examples are the Skyline Plaza Complex collapse in Virginia (1973), the Harbour Cay building in Florida (1981), the Sampoong Department Store collapse in South Korea (1995) and the Gretzenbach underground parking garage collapse in Switzerland (2004). The reasons behind these failures include deficiencies in design, errors during
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