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‘In buildings you traditionally design a facade to resist wind and gravity but rarely something as extreme as a blast load’

Engineer Raymond Lumantarna researched how bomb blasts can affect buildings with glass facades.

 

‘When there is a blast incident there are glass fragments flying everywhere and it becomes more of a hazard rather than a structure for protecting people. I analysed how buildings can perform better under blast loads. 

A building facade normally consists of glass and an aluminium frame. If your frame is too stiff, it is vulnerable. Under blast pressure the glass will most likely shatter. But if your support is too flexible, the frame will bend out of shape and the glass will break anyway. 

A good balance is somewhere in between. Imagine it like this. If you drop your drinking mug on a concrete floor you will probably break it. But if you drop it on a carpet floor it will be OK. 

‘Terrorism is a threat but if we made every building like this we would just have really big ugly concrete bunkers everywhere.’ 

I calculated the probability of failure of the glass under different blast loads.

The bomb could be anything from 10kg of C4 to 200kg of a homemade device composed of fertiliser and gasoline. The pressure could be at a close or far range. The calculations must also consider the probability of this occurring. 

A blast explosion is an extraordinary event. Buildings are not designed to resist blasts unless they are targets of terrorism. Government buildings are an example or, infrastructure,  such as telecommunications towers. 

Sometimes, terrorists attack landmarks because they are iconic buildings. They’re aiming for an emotional impact rather than a financial one. 

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In terms of dealing with a blast threat, you always have several things to consider. The first is changing the building’s function so it’s not a target. The second is minimising the threat by putting barriers or fencing around the area and security screens outside the building so you can’t bring explosive devices inside. Then, as a last resort, you think about strengthening the building.

For mining facilities or gas storage plants, this doesn’t really matter because they are risk buildings, not targets. Accidental explosions can happen, so you need to strengthen the building and have safety bunker rooms. 

We conducted an experiment in Woomera, an air force testing field in South Australia. It was a large-scale blast and we used the results of the test to validate the calculation we did with the computer modelling.

We had to move two kilometres away from the blast area and when the explosion went off we only saw a small puff of smoke on the horizon. It’s a multi-million-dollar exercise so you don’t really have the privilege of doing the experiment as many times as you like. 

There are a long series of trials that happen every two years and I went twice. To make the glass facade system blast resistant, you have to oversize everything.

‘If you design the entire building in a balanced way at the beginning, then you don’t have to oversize every single component in your facade system later.’ 

First, you have to design a really thick glass, which you construct like a sandwich. There’s one layer of glass, a layer of plastic laminates called polyvinyl butyral (PVB), and another layer of glass. 

Then you need to design a really thick frame, usually with steel because aluminium is more flexible and yields at a lower pressure. Your bolts also have to be oversized if a building is not initially designed to resist blast loads. 

Terrorism is a threat but if we made every building like this we would just have really big ugly concrete bunkers everywhere. Architects don’t like that because it’s not aesthetically appealing. Glass is hazardous but there are a lot of reasons why we use it. It is visually comforting.

You have a lot more sunlight coming into your building and you don’t use as much energy in artificial lighting. It’s also quite expensive to make your building blast resistant. In future, we need to move away from oversizing.

If you design the entire building in a balanced way at the beginning, then you don’t have to oversize every single component in your facade system later. There is no such thing as “blast proof” but we can design structures to resist blast loads to minimise damages and injuries.’

Raymond Lumantarna’s  thesis is titled:“Performance of glass facade systems subjected to blast loads”

My PhD is an irregular series in which The Citizen speaks with recent Melbourne University PhD graduates. 

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THE CITIZEN is a publication of the Centre for Advancing Journalism. It has several aims. Foremost, it is a teaching tool that showcases the work of the students in the University of Melbourne’s Master of Journalism and Master of International Journalism programs, giving them real-world experience in working for publication and to deadline. Find out more →

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