IIT Madras develops framework to protect critical infrastructure against ballistic missiles

Researchers at the Indian Institute of Technology (IIT), Madras, have developed a framework that can boost protection of critical infrastructure in the country against the threat of ballistic missiles, according to officials.

The framework will help designers develop innovative solutions for improving the ballistic resistance of reinforced concrete (RC) panels, they said.

The findings of the research were published in reputed peer-reviewed journal "Reliability Engineering & System Safety".

Using computational simulations, the researchers studied the impact of missiles on RC, which is the main material used to construct vital structures ranging from military bunkers, nuclear power buildings and bridges to runways.

According to Alagappan Ponnalagu, assistant professor, Department of Civil Engineering, IIT Madras, concrete structures face highly localised damage such as penetration, perforation, scabbing, spalling and crushing under projectile impact load.

"Due to the strategic importance of these structures, it is necessary to protect them against projectile and debris impact, which can result in localised damage or even the collapse of the entire structure," he said.

Ballistics is a field of engineering that deals with the launching, flight behaviour, and impact effects of projectiles such as bullets, bombs, and rockets. This science is used not only for designing bunkers, but also for designing the walls of nuclear power buildings, bridges, and other protective structures.

The researchers conducted the study during ‘Finite Element’ (FE) simulation, a computational technique used to simulate and analyse physical phenomena in engineering and science.

"FE simulation relies on the Finite Element Method (FEM), a numerical approach for solving complex problems involving partial differential equations. These problems often arise in fields like structural mechanics, among others. The researchers focused on the development of the novel performance-based design framework based on ‘Depth of Penetration’ (DOP) and Crater Damage Area in the RC panels.

"In addition to that, a probabilistic formula for estimating the crater diameter in RC panels is proposed.The study is helpful not only in terms of providing the ballistic design framework and probabilistic crater quantification formula, but also in understanding the ballistic behaviour of RC panels," he said.

Ponnalagu explained that ballistic design is crucial for widely utilised concrete structures in today's unpredictable world.

"Usually, extensive experimental and numerical studies have been done to investigate concrete panels, resulting in design guidelines for local damage parameters. However, with the advent of performance-based design, the ballistic design of concrete structures lacks a comprehensive design philosophy. Moreover, while quantifying damage parameters, incorrect and inconsistent results are obtained by using deterministic empirical formulations.

"We have now provided a reliable design formula for estimating crater diameter in addition to the development a novel performance-based ballistic design framework for RC panels. This study is helpful not only in terms of providing the ballistic design framework and probabilistic crater quantification formula but also in understanding the ballistic behaviour of RC panels," he said.

The researchers now plan to extend this study to develop much-needed lightweight, cost-effective and sustainable blast-and ballistic-resistant modular panels that can be used in the construction of bunkers along the borders and highly inaccessible areas for the Indian Army.

"We have proposed a novel performance-based design framework for RC panels based on damage states, namely DOP and crater diameter. Each damage state has four damage levels and is effectively coupled. Hence, the framework is a novel design philosophy ensuring resiliency against projectile penetration and crater formation of RC panels," said Roouf Un Nabi Dar, research scholar, IIT Madras.

"On the other hand, the local damage response in terms of crater formation in RC panels was studied under projectile impact. A probabilistic approach is taken to formulate a reliable formula for quantifying unexplored crater damage, based on well-established Bayesian methodology for RC panels that takes into account uncertainty," Dar said.