Experimental investigation of band-beam slabs subjected to close-range blast loading

Portable explosions in the form of backpacks and suitcases have been at the forefront of various terrorist activities due to their ability to create unrest in crucial infrastructure such as railway stations. At close range, these portable explosives, with charge sizes ranging from 2 kg to 10 kg, can reasonably damage vital structural elements of a building. For example, the debris produced by breaching one slab can overload and damage the slabs below in a multi-storey structure or pile up to block the access and continuous functioning of a building during rescue operations. A "band-beam slab" or "slab with a shallow beam" is one of the most used slab types in modern multi-storey buildings, especially on basements and lower floors. The band-beam slabs are commonly used to save headspace and floor-to-floor heights of multi-storeyed buildings. Therefore, investigation of the performance of band-beam slabs under close-in detonation is an interest of crucial infrastructure projects. To this end, the work presented in this paper investigates the performance of band-beam slabs subjected to close-in detonations. Thirteen band-beam slabs were subjected to close-in detonations against Composition-4 (C4) charges of sizes varying from 2.5 kg to 4.5 kg. The panels were designed to withstand the overall blast load following the typical design guidelines. However, some variations were introduced in the design to observe the effect of (i) slab reinforcement ratio, (ii) primary longitudinal reinforcement ratio of the beam, (iii) shear link size and spacing in band-beams, and (iv) scaled stand-off distance. In general, all test specimens experienced minor to moderate damage. At the same time, it is observed that the effect of the shear reinforcement ratio and detailing of the reinforcement play a significant role in reducing the spalling and crater formation. The observations have been compared with the UFC-3-340-02 guidelines for spalling and breach and found that experimental results reasonably agree with UFC predictions. Finally, based on the observations, design recommendations in terms of additional reinforcement to control and mitigate spalling, cracking and scabbing were proposed.