Designing for Blast
Table of Contents
Introduction
Design serves many different purposes in structural aspects and for buildings. As society becomes more complicated, there are more factors that have to be considered when faced with unexpected scenarios. Concerns for more buildings include designing for prevention and protection against explosions, especially for government and military based buildings. Dynamic loads include incidents such as natural disasters and require meticulous consideration and calculation [1]. Designing for blast means that incorporating the possibility for an explosion has become a primary objective for the scope of the building and requires a series of various steps and impacts to be addressed before any decisions can be made. Although protection of people within the building would be the main concern, there are numerous other trade-offs and criteria that have to be assessed to be able to conclude with the best design [2].
Building After Explosion [3] |
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Purpose
Threat
For terrorist activities, usually the two main considerations are for vehicles and weapons [2]. In terms of watching out for vehicles, the potential threat emerges from all sides of a building that is parallel to or facing a street. The vehicle is considered an air-blast load and decreases with distance so the primary danger is near the base of the building. For prevention of vehicle attacks apart from screening are intrusions such as anti-ram barriers along the perimeter of the building as well as utilizing the form of the landscape to create an obstacle course can be effective. However, oftentimes the vehicle itself is not the only threat because they can be used as a diversion or container for a secondary attack such as an explosive or hand-held weapons like a gun so further protection is needed.
There are a multitude of various weapons that produce a hazard to the lives of people but in regards to a building, the greatest pressure comes from explosives. Factors to be aware of are that the impact of explosives decrease very quickly with time and space and usually the pressure produced increases linearly with the size. Although the actual explosion only lasts a couple milliseconds, the area of the shock wave can hit the entire building and even the surroundings.
Effects of an Explosion:
Vehicle weapon threat [2] |
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Sequence of Air-blast Effects [2] |
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Building Damage
Damage done to a building can be separated into two categories of direct air-blast and progressive collapse [2]. Direct air-blast refers to the source of the explosion and takes into account the damage caused by the high-intensity pressures near the incident. In some cases, this may cause the exterior envelope to collapse in a specific area. How severe the damage ends up being, is dependent on the weapon size, distance from the building envelope, and what materials it is made of.
After the initial failure in a localized area, the extent of the damage spreads out to further elements, called progressive collapse. This may propagate laterally outwards or even vertically upwards and downwards. Not all buildings face progressive collapse since this depends on the features of the building.
Design Criteria to Prevent Progressive Collapse:
Structural Aspects and Specifications
Walls
Poured in Reinforced Concrete
Pre-cast Concrete
Other Materials
Curtain Wall
Blast Resistant Sacrificial Wall [5] |
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