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The IUP Journal of Structural Engineering :
The Effect of Blast Load on Three-Dimensional High-Rise Steel Frame Structure
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The use of vehicle bombs to attack city centers has been a feature of campaigns by terrorist organizations around the world. A bomb explosion within or immediately nearby a building can cause catastrophic damage on the building’s external and internal structural frames. The objective of this study is to shed light on blast-resistant building design theories, the enhancement of building security against the effects of explosives in both architectural and structural design process and the design techniques that should be carried out. To analyze high-rise steel structure for blast loading, we have to generate a model of high-rise steel structure using E-tabs software which can resist all types of loading such as dead load, live load, seismic load using IS: 800 (2000) and IS: 1893 (part-1). The same structure is again analyzed for blast loading, due to which partial collapse or total collapse may occur which can be studied. The finite element software ETABS-2015, and a 3-dimensional model consisting of 20 stories of steel structures are first created, then blast loading is calculated and assigned using time history function. Blast loading at various standoff distance is calculated using IS: 4991 (1968). This blast load is assigned to structure and its behavior is analyzed. The parameters checked after analysis of blast loading on structure are demand capacity ratio, bending moments, shear force, deflection and story drift.

 
 

Explosive loading incidents have become a serious problem, which needs to be addressed immediately. Structures loaded by explosive incidents are constructed in concrete or steel frames and their behavior under blast loads is of great interest. Besides the immediate and localized blast effects, one must consider the serious consequences associated with collapse that could affect people and property. Failure of structure occurs when a structure has its loading pattern or boundary conditions changed such that structural elements are loaded beyond their capacity. In the past, structures designed to withstand normal load conditions were over designed, and have usually been capable of tolerating some abnormal loads. Modern building design and construction practices enabled one to build lighter and more optimized structural systems with considerably lower over design characteristics. Essential techniques for increasing the capacity of a building to provide protection against explosive effects shall be discussed both with architectural and structural approaches. Damage to the assets, loss of life and social panic are factors that have to be minimized if the threat of terrorist action cannot be stopped. Designing the structures to be fully blast-resistant is not a realistic and economical option, however current engineering and architectural knowledge can enhance the new and existing buildings to mitigate the effects of an explosion.

An explosion will create a blast wave, as the air-blast shock wave is the primary damage mechanism in an explosion. The pressures it exerts on building surfaces may be several orders of magnitude greater than the loads for which the building is designed. The shock wave will penetrate and surround a structure and act in directions that the building may not have been designed for, such as upward force on the floor system. In terms of sequence of response, the air-blast first impinges on the weakest point in the vicinity of the device closest to the explosion, typically the exterior envelope of the building. The explosion pushes on the exterior walls at the lower stories and may cause wall failure and window breakage. As the shock wave continues to expand, it enters the structure, pushing both upward and downward on the floor slabs. The damage caused by explosions is produced by the passage of compressed air in the blast wave. Blast waves propagate at supersonic speeds and get reflected as they meet objects. As the blast wave continues to expand away from the source of the explosion its intensity diminishes and its effect on the objects is also reduced.

 
 

Blast loading, Demand Capacity Ratio (DCR), Bending moments, Shear Force, Deflection, Story drift, Partial collapse