She continues, “There are certain conditions in each standard that are slightly different for the determination of the load resistance of glass to be used in building design. The strength charts for ASTM and the original charts for the CGSB Standard were published to accommodate four-side supported glass under uniform lateral pressures. This was the methodology used in 1989 in both standards. The ASTM Standard has been continuously updated since 1989 with the addition of additional glass load resistance thickness selection charts for various support conditions and glass constructions. The CGSB 12.20 standard has not been updated since its original publication date in 1989.”
Webb says the committee developed a task group to look at the two standards and make a recommendation on how to address IGMA’s code change request. “This was a relatively large task so it wasn’t possible to address this in time for the 2010 Canadian code cycle,” she says.
The change is expected to provide “much needed flexibility and the tools to ensure appropriate glass design for current products,” according to Webb.
“The most recent versions of the E 1300 Standard have incorporated the load duration for the charts in the standard to be at three seconds for the initial uniform load,” says Webb. “There were factors applied for certain glass combinations to accommodate long-term loads such as snow loads for skylights and other slope glazing conditions. The practice has also incorporated specific charts for monolithic glass, laminated glass and glass-supported on one, two, three or four edges and also includes triple-glazed units.”
Webb says a public comment period will be held for the proposed change, though it has not opened yet.