A new design technique will protect people in iconic buildings from glass related injuries in the event of a bomb explosion, researchers from Queensland University of Technology say.

In their study, published in the journal Engineering Failure Analysis, QUT researchers Dr Ruwanika Piyasena, Professor David Thambiratnam, Professor Tommy Chan and Adjunct Professor Nimal Perera examined both the shockwaves from the ‘maximum’ credible load of an explosion along with how the glass structure in the building facade reacts to the blast in order to devise the best solution to prevent the glass from shattering in the event of a bomb.

They found that by adopting a layered system whereby two panels of laminated glass panels were separated by a shock absorbing air layer as well as by making the cable trusses stronger, the window system would crack but the glass would not shatter.

Under this system, the energy associated with the blast was absorbed through the air layer and the members of the supporting system.

Thambiratnam said the study went beyond previous research and looked not only at how the glass responded to an explosion but also modelled the explosive source, the pressure wave transmission and fluid-structure interaction.

“We modelled the shock waves that travelled through the air and then we studied how it hit the structures,” he said.

“The glass is certainly going to crack, but this interlayer holds the particles together.”

Piyasena said the solution could be applied not just to new builds but also to retrofits of existing ones, whereby the addition of a second layer of skin and an absorbing air layer onto existing facades could help to bomb-proof existing facades.

“Development of the fully coupled modelling technique enabled the realistic modelling of double skin facades and identified the effects of appending an additional skin,” Piyasena said.

The double skin facades would be two glass skins separated by an air corridor.

“This double skin feature can be used as a retrofitting method for converting existing conventional facades to blast-resistant facades,” Piyasena said.

“Attaching additional skin will be more economically feasible than removing the existing façade and replacing with a new blast-resistant facade, as double skin feature will also provide energy efficient characteristics.”

The researchers specifically looked at cable truss facades, which are mostly used in hotel lobbies, shopping malls and airport terminals, where the structure of the large glass area is secured by twin convex and concave cables behind the glass.

They examined case studies of real blast scenarios and found that up to 90 per cent of blast-related injuries in bomb attacks were due to flying glass fragments and other façade debris.

Thambiratnam said previous research had used an uncoupled method of analysis which calculated blast pressure hitting a façade as uniformly distributed, whereas examining the explosive waves in an explosion showed that blast pressures at lower levels of the facade would be higher than those at the upper level.

Piyasena said the developed modelling techniques can be augmented and altered to study the response of debris impact such as hailstorms on cable supported glass facades (by incorporating the load model for the debris in a coupled analysis).

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