GlassCon Discussions Take a Look at Structural Glass Designs

Codes and standards have a major role to play when it comes to designing and constructing a safe building—possibly even more so when glass becomes a structural element. A number of discussions involving structural glass codes, standards and design were on the agenda today during GlassCon Global, taking place this week in Philadelphia.

Richard Green with Front Inc. began with a discussion about the development of an ASTM guide to structural glass, which has been in the works for about two years. Green explained that there is sometimes resistance to designing and building structural glass applications because of the risk of not get building approval due to there not being any type of building code to go by.

While ASTM E1300 is available, it is for window glass in buildings. The new standard, on the other hand, is for glass structures.

“It is for delivering reliable strength,” Green said, explaining that the aim is to prevent breakage. He added that the structural standard also addresses the consequences of assuming at least one element breaks.

Likewise, while E1300 is a probability based for windows, Green explained the structural guide will be stress/stability based. Calculations will be based on load resistance factor design and analysis will be system based rather than element based.

“Glass is unique,” he said. “It is transparent, brittle and any crack is regarded as a failure.”

In terms of designs, he said to assume the glass will break and then make it sensible. He also covered post failure capacity, explaining there is interest in what happens after the glass breaks.

As for the standard’s development, Green said there the working group is in place, but having the standard’s language developed is still a couple years away.

Another session today looked at glass structures and seismic design. Andrea Hektor with KPFF Consulting Engineers, who led the presentation, said the basic challenge is a general lack of knowledge/lack of code guidance about structural glass in the United States. She pointed out that limited knowledge sharing prevents barriers and things of that nature.

Common mistakes, she said, can include the incorrect glass usage; incorrect glazing thickness; allowable stresses; incorrect application of loads, etc. She said when getting into seismic regions and seismic designs, even less information is available (such as a design guide). There are technical manuals and documents available for other materials, but not glass. She noted, however, they can look to those documents as a guideline.

Hektor spoke of the importance of material behavior and understanding how something is going to fail. This can include the behavior of glass under shear loads; behavior of laminated glass under shear loads; silicone response under cyclical loading; allowable loads for silicone under seismic loading, etc.

Vincente Montes-Amoros with CDC spoke today about glass breakage in glass railing systems, covering both code and design considerations.

Considerations, he said, include the need for safety glass; aesthetic purposes; and code requirements for egress and performance.

Safety glazing is required by the code, he said, adding that there are specific tests with which the glass needs to comply, such as impact testing and identification on the glass.

Specific to tempered glass, he said a consideration is the possibility of nickel sulfide inclusions. “The thicker the glass, the more probability of an inclusion,” he said.

He also pointed out that one of the most important requirements in the code says each guard section must be supported by a minimum of three glass balusters. This ensures that if one breaks, there are still two others in place.

Other structural glass related discussions covered topics related to cold bending and thermal bending of glass, as well as glass as a support structure.

GlassCon Global continues tomorrow. Stay tuned to USGNN.com™ for more reports from the conference.