No longer is Mother Nature the only threat to buildings; the prevalence of man-induced disasters continues to increase. Thus, blast resistant building design is pioneering this new era of construction.
Explosions are instant, unpredictable and can have extreme ramifications. Whilst the effect of blast loads on buildings from explosions of any form cannot be perfectly predicted or anticipated, measures can be put in place to prevent building collapse and fatalities.
Of course, not all construction projects need to consider blast resistant design, but it can apply to industrial construction for clients that house explosive goods or dangerous gases. Buildings with high bomb threats usually include public service buildings such as court houses and government premises.
BACKGROUND OF EXPLOSIONS
An explosion can occur on ground level known as a surface burst or in mid-air, called an air burst. Each has different ramifications to its surroundings due to varying waves of effect. A ‘Match Stem’ is the combination of the initial wave and reflected waves forming together.
The initial explosion wave can create intense stress on structural building materials if detonated close enough to fundamental components of the building’s structure; resulting in the crushing or strength failure of a building.
- Air Burst
Occurring on ground level, a surface burst explosion will send shock waves known as the initial wave out first. This wave merges with the reflective waves to form one single, powerful wave of destruction – the match stem. This can be very dangerous if detonated in the confines of a building, as the reflection waves will bounce off the building and continue to increase the power of the incident wave.
- Surface Burst
Detonating above ground surface, an air burst can cause reflection waves to hit the ground before the initial blast wave. As the waves continue a Match Stem is formed by the initial wave and reflected waves interacting.
DESIGNING A BLAST RESISTANT BUILDING
Whilst there are many factors to consider when designing a building, such as functionality of the building, fire regulations, accessibility, aesthetical concerns and of course budget restrictions; blast resistance has now found its way on this list of considerations as well. In some cases, these requirements can conflict, thus individual discretion is applied.
Below are some simple considerations to apply during the design phase in order to minimise bomb threats:
- Strategic Building Placement – by placing a building as far away from access points as possible creates stand-off distance between an external bomb and the building itself. This maximises potential protection from shock waves of a bomb detonated in a street or neighbouring building. A minimum 30-meter stand-off distance is recommended where possible as well as installation of obstructions such as bollards, trees, fencing/walls and street furniture to absorb reflection shocks.
- Structural Form – it has been proven that arched and dome structures cope best under the stress of blast loads. Single storey buildings are much more blast resistant compared to multi-level buildings.
- Internal Layout – obviously any explosion will cause some form of damage. Protecting the most valuable asset in a building should be considered in the internal layout. Roads and access points are considered the most high-risk areas of detonation. That, combined with the knowledge of single storey structures being the most blast resistant, suggest valuable assets should be stored on the ground level of a building in the furthest point away from entry points and main roads.
- Fire Resistance – in the majority of cases, explosions cause fires and as such internal members of a building should be of a high fire grade resistance to prevent further damage.
- Bomb Shelter Areas – Whilst buildings can always be rebuilt, a life can never be replaced. Including bomb shelter areas for people in the safest area of a building away from blast effects is the most important consideration that can be taken. Located away from windows, external doors and walls and on a lower level of a building, bomb shelter areas need to be large enough to accommodate the expected number of people in a building, have escape access points and lines of communication to the outside world.
Whilst fortunately we’ve not been required to undertake projects which require extensive explosion resistance, Akura’s Architects, Engineers and Draftsmen consider collapse limit design for every building we construct. This means that the behaviour of structure when extraordinary load is applied is examined to determine if the building is ductile enough to withstand an explosion or if it is likely to collapse. For some buildings where functionality requirements trump bomb resistance, it is important to know the likelihood of a buildings collapse in the case of a bomb threat. This can determine the best course of action and prevent injury and loss of life.
As Akura manufactures all our own structural steel from a raw product to finished assemblies, we have the capacity to build enhanced beam to column connections that will be adequate in withstanding blast loadings and prevent collapse of a structure. An enhanced beam to column connection includes strengthening plates on all four sides of the connection from the beam to the column.
Full height concrete walls have been the selection of choice for many experts in the field of bomb resistant building designs. Commonly used to build bomb shelters, concrete panel walls have the structural integrity to withstand blast effects and keep humans safe on the inside. Akura’s precast concrete panel factory has the capacity to construct load bearing precast concrete panels like those used to build bomb shelters.
Although no explosion can ever be fully anticipated and there is competing factors that conflict with blast resistant building designs, the safety of a building’s occupants is always at the forefront of Akura’s designs and any reasonable prevention method will be considered in the event of a man made or natural disaster to provide the safest and most durable structure possible.