Dynamic Design: Evolution and Opportunities in Blast-Resistant Glazing

By Ellen Rogers

The devastation from events such as the Oklahoma City bombing and the 9/11 terrorist attacks created a heightened awareness surrounding the importance of protective glazing products, such as blast- and ballistic-resistant glazing. In the years that followed, many system manufacturers successfully tested and developed products to help mitigate against these threats.

What’s the market like for blast-resistant glazing today? These products are mandated for use in some applications, such as federal government buildings, and continue to be specified on certain high-level security projects, as well.

Jeff Heymann, vice president of Benson Industries, says his company continues to work on projects that call for blast-resistant systems.

“We still see it on government projects, as well as financial institutions and, most recently, ground floors of a religious organization.”

Increasing Awareness

Some glazing products have seen significant changes across multiple decades, though that hasn’t necessarily been true for blast-resistant glazing.

According to Tim Floyd, senior window blast design engineer for Applied Research Associates Inc., commercial window design for blast loads was in its infancy 20-30 years ago.

“September 11, 2001, brought additional attention to the terrorism threat that had been stoked by the 1995 Oklahoma City bombing and the 1993 World Trade Center bombing. Over the last ten years, the complexity of systems used in blast design has increased considerably,” says Floyd. “Additional creative liberties have been taken with window design for systems requiring blast design. These include point supported glass, systems supported by cables and very large glass curved atria. Complex finite element modeling can now be used to accurately model these systems for short duration dynamic loading.” He adds that dynamic analysis during product development can minimize the probability of an unbalanced weak point in the system.

“In other words, [you want to] limit the likelihood of a component of the system being much weaker than the overall system,” he says.

While finite element modeling and analysis has expanded the number of opportunities to use blast-resistant glazing, it’s still important to remember these products are unique compared to traditional glazing. For example, with blast systems the glass has to be thicker overall and the framing system has to work in concert with the elasticity of glass.

Brian Dawley, senior technical services specialist with Viracon, says that in the early days of blast design the mindset was to simply mitigate breakage.

“Now that’s evolved to a much more pliable curtainwall/glass material that still provides protection while not allowing debris and glass load into the building,” he says.

“It’s not so much that the blast products have changed, but rather the understanding of how to design the system to accommodate the forces,” says Heymann, explaining that blast products are designed to an impulse force. “[The system’s] design includes the frame, glass and anchorage, and all have to work together to make sure the load of the structure is dissipated throughout.”

Ron McCann, who recently retired from Viracon, says while blast material itself hasn’t changed all that much, products have had to evolve in response to requests from architects.

“Architects want extremely large lites of glass and that brings a new challenge,” he says, explaining that as the size of glass increases, the thickness may need to as well, in order to meet the blast design load, which increases the overall weight of the unit.

Looking Ahead

High-security/high-risk projects, such as government buildings, will continue to call for blast-resistant design. Certain factors, however, will affect future development of blast-resistant products.

“As far as evolution of the material, I think it’s about where it’s going to go unless something radically different comes along,” says Dawley.

Floyd adds that there is a constant push to expand what is possible to do with glazed systems—and that includes blast products.

“Using natural light verses artificial light has been pushed by industry. Additionally, there have been improvements in thermal efficiency of glazed systems,” he says. “Glass can be used in many aesthetically pleasing ways and creative innovation has pushed the envelope.”

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