EVALUATION OF REINFORCED CONCRETE PANELS UNDER BLAST LOADING

Abstract

In recent past, civilian buildings and military structures have been unexpectedly exposed to the risk of terrorist attacks, particularly in the form of vehicle bombing or other portable detonation devices and explosives. The high mobility of these potential threats is a major challenge to the structural safety. Historical events, indicate that progressive/disproportional collapse of structures can result from localised intense loading. In this respect, prediction of impacted components becomes immensely valuable for realistic assessment of structural blast resistance In the recent years the construction industry found the world has been challenged to design and build civil and military structures capable of withstanding explosion induced blast wave loads both from terrorist attacks and other acts of war. This challenge is very relevant to many countries around the world, including our country. In the present context of our country, there is an increase in terrorist activities in urban areas, which are at reasonable distance from J & K and north eastern region affected by terrorism. Also with the rise in naxalism, no place could be considered safe. One of the most common threats would be an exposure to blast using explosives which could be carried and used easily. In view of the above it is pertinent to ascertain the performance of common structural elements and materials subjected to the blast loading. Furthermore, it becomes important to understand the response of reinforced concrete as a structural material when subjected to large stresses and strain rates through explosive loadings. Reinforced concrete is a principal construction material used for civilian buildings and military constructions. These structures might be subjected to extreme loadings during their service life, such as blast and explosive loading which could produce an overload much greater than the design load of a structure in a very short period of time. This may result in severe damage to the reinforced concrete structure and cause tremendous casualties and property loss. The RCC slabs are the most common structural elements of any construction and are highly vulnerable to blast loads. The analysis and design of slab as a structural member that are subjected to blast loading are often very complex. Blast loading in general, is an extremely severe loading condition characterized by the application of a ` iv force of great intensity within the short time duration. This type of loading can lead to different types of global or localized damage, including flexure, penetration and scabbing, spalling, perforation and punching shear failure. In the design of protective structures, concrete slabs play a vital role and are often used to provide effective protection against blast from impact of mortars or the explosion of high explosive shells in contact or in close proximity. With a reasonable configuration and proper reinforcement, the protective structure could sustain a specified level of blast without global failure. However, the concrete slabs may generate spallation on the distal surface, posing threats to the personnel and equipment inside the structures. Although reinforced concrete slabs are the most common structural elements, in spite of the large no of concrete slabs used, the effects of their behavior under blast loading are not always taken into account. Also since the conduct of explosive tests are dangerous and costly, the number of studies conducted on this related topic has been limited. In the present study, 1000mm x 1000mm x 100mm slabs have been subjected to blast by three different weights of explosive at three varying distances. The weight of the explosive used is equivalent to the explosive content of that in the Indian mortars and High Explosive (HE) shells of rocket launchers. The experimental investigation of the blast impact on reinforced slabs enabled the understanding of the mechanics of deformation of these panels. The outcome of this work would enable a better understanding of the characteristics of reinforced concrete bunkers in the field areas subjected to blast by mortars and rocket launchers .The study was aimed to examine the extent of blasts the concrete reinforced slabs can withstand and eventually enable the optimization of the design of these protective structures.