Abstract
Reinforced concrete (RC) slabs and panels are commonly encountered in critical infrastructure and industrial facilities with a high risk of close-range explosions due to accidents or terrorist attacks. Close-in detonations lead to high intensity concentrated loads which can cause a premature brittle punching failure of the member. The assessment of such type of failure mode is challenging since the loading source varies its magnitude in space and time. This paper proposes an analytical method by which the occurrence of punching (or otherwise) is assessed by comparing the dynamic shear demand and capacity (supply). An exponentially decaying distribution of reflected overpressures on the RC surface is presented for this analysis. The punching shear demand is estimated from the pressure and inertial forces acting in the free body diagram. The dynamic punching shear capacity is obtained using the Critical Shear Crack Theory with small slab deformations which are predicted from an equivalent single-degree-of freedom model. The proposed approach takes into account the impulsive behaviour of the member leading to a higher punching capacity and provides better predictions than using existing formulae for punching which are based on tests with quasi-static loading and deformations. The proposed analytical equations are further supported by numerical explicit finite element models providing useful information of crack development, dynamic reactions and deflections. The application of the proposed method has been illustrated and validated by comparison with various tests with scale distances from 0.2 to 1.5m/kg1/3. A practical example is presented to illustrate the applicability of the proposed method.
Highlights
The increased threat of terrorist attacks as well as the occurrence of accidental explosions within or in close proximity to an engineering structure often leads the engineer to consider the actions of blast loading on the structure being designed
A fundamental characteristic of the Critical Shear Crack Theory (CSCT) is that the punching capacity is related to the slab rotation which is proportional to the opening of the shear crack which is an indirect measure of the strains in the concrete at failure
Close-range blasts can result in punching shear failures adjacent to the detonation in reinforced concrete (RC) slabs or panels due to the localised loading and high shear demand in this region during the short load duration
Summary
The increased threat of terrorist attacks as well as the occurrence of accidental explosions within or in close proximity to an engineering structure often leads the engineer to consider the actions of blast loading on the structure being designed. A number of situations can arise where blast loading can cause punching shear failure in a RC structure, viz. (1) and (2) are applied in this work to estimate the level of damage and to compare it with the predictions from the proposed model which only looks at punching. Whilst simple, these formulae are purely empirical and do not distinguish between breach and punching. As highlighted in Silva and Lu [3] there is no analytical method of assessing the occurrence of punching in RC structures subjected to blast loading. The proposed approach is validated against existing experimental data and it is further supported by numerical simulations
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