Thermal stress conditions in heat-strengthened spandrel glass was the opening discussion topic during the Glass Association of North America’s (GANA) Tempering Division meeting. The group met today as part of GANA’s 2015 Annual Conference, taking place at the Paris Las Vegas Resort and Casino in Las Vegas.

Industry consultant Bill Lingnell spoke during the GANA Annual Conference tempering division meeting about thermal stress considerations.
Industry consultant Bill Lingnell spoke during the GANA Annual Conference tempering division meeting about thermal stress considerations.

Bill Lingnell of Lingnell Consulting Services talked to attendees about various conditions that can cause thermal stress. These can include altitude, building design, winter and summer temperatures, building orientation and edge conditions, among others.

As Lingnell explained, “Thermal stress happens when there are differences in heating in the glass.” This is something glass manufacturers and fabricators deal with often in their processes, but in today’s session, he focused on conditions that happen in the field rather than within the plant.

He explained that the majority of failures he has evaluated usually start at the edge of glass and are caused by differentials in heating. Differentials in heating are caused when the edges of the window glass installed in a frame is shielded from the direct effects of solar radiation or heat sources, while the central areas of the glass are exposed to the direct effects of the solar radiation.

Speaking on spandrel conditions specifically, Lingnell said heat-treated glass is often recommended for these applications. For some extreme conditions, heat-strengthened glass may not be enough, and fully tempered glass, which is the lowest risk, is needed. Annealed glass poses the highest risk of thermal stress.

He added that solar absorption is the amount of total solar radiation absorbed by the glass and is one of the highest-ranking items relating to thermal stress evaluation in annealed glass.

Lingnell also explained that thermal stress is dynamic. It does not happen overnight, but over a period of time.

Some Items for investigation when considering these breaks, Lingnell explained can include:

  • Structural issues with ceramic enamel-porosity and fineness of grinding process;
  • Coefficient of expansion of enamel and glass concerns;
  • Application techniques and enamel thickness;
  • Temperature variations during the heat treating and cooling processes;
  • Absorption properties of color; and
  • Quality assurance programs at suppliers and fabricator.

Lingnell offered a look at cases that have occurred in the field. He showed how thermal stress incidents can be different on different buildings and climate zones. Other considerations he covered included different characteristics of the glass, such as coatings, whether the glass is an insulting unit or monolithic, etc.

Also during the tempering meeting, the groups reviewed and discussed several documents and manuals. This included an update to the Engineering Standards Manual, as well as an update to the Proper Procedures for Cleaning Architectural Glass bulletin, which is a joint effort with the International Window Cleaning Association.

GANA’s Annual Conferenced runs through Sunday and will be followed by its Building Envelope Contractors Conference. Stay tuned to USGNN.com for more news and reports from these two events.