IGMA: April 2012
By Bill Lingnell
Refining load resistance standards
By Bill Lingnell
The past two articles focused on the history and updating of the ASTM
Standard E-1300 “Standard Practice for Determining Load Resistance of
Glass in Buildings,”
The past two articles focused on the history and updating of the ASTM Standard E-1300 “Standard Practice for Determining Load Resistance of Glass in Buildings,” which basically brought us up to date on where the current version ASTM E 1300-09a sits. This January, a special task group meeting was held in New Orleans to craft much of the future events and potential modifications for the standard. Active committee members from the United States and Canada attended this meeting in an effort to evaluate and present the items that will be balloted through the ASTM process. The resulting ballot seeks to update, add to and enhance the procedures and methods that have been requested by the architects, specifiers, designers, engineers, and contractors that use the standard, and the code groups that reference the standard.
The ballot that is presently being reviewed and voted on by members of the ASTM E 06 sub- and main committees has a number of additions that enhance the standard. For example, the upper load limit has been increased from 10 to 15 kilopascals for coverage in the standard for uniform load conditions. The existing non-factored load charts have been revised with new charts to provide load lines for the increase in the load condition. An addition of a non-factored load chart and deflection chart for 25-millimetre glass will now be incorporated into the standard. These additions will aid in the usefulness of the standard for expanded load capacity and thickness capabilities.
Glass type factors for wired, patterned, etched, and sandblasted glass have been incorporated into a table for monolithic or laminated glass. A special note that excludes drilled, notched and grooved glass, or glass with surface and edge treatments that alter the glass strength, is also incorporated in the revised standard.
The ballot will also incorporate a new appendix that has the potential to be a major improvement to the standard. The appendix is titled “Method for Determining the Load Resistance of Heat-Treated Glass.” This will be an alternative method of calculating the load resistance of heat-treated glass for a three-second load duration using a heat-strengthened type factor when considering heat-strengthened glass, or a fully tempered type factor when considering fully tempered glass. The procedures for determining the load resistance will be similar to the methodology presently used for annealed glass, except special equations have been derived to accommodate the surface compression stress for the heat-strengthened glass and fully tempered glass. There are non-factored load charts for four-sided support conditions using a three-second load duration for a probability of breakage of eight lites per 1,000 for heat-strengthened glass and a set of charts for fully tempered glass also. The residual compression stress in the surfaces of the heat-treated glass from the heat-strengthening or tempering process is part of the equation that will give the user the appropriate type factor to use with the charts in determining the load resistance. The appendix of an ASTM standard is a non-mandatory portion of a standard; however, it is anticipated that this may end up being a valuable tool for users of the standard.
The main committee will meet in April in Phoenix to discuss the results of the ballot and decide the direction for the next version of the ASTM E-1300.
Bill Lingnell has over 46 years of experience in the technical field of glass and architectural products. He holds three Masters of Science degrees in engineering: civil, mechanical and engineering science. Lingnell is the technical consultant for the Insulating Glass Manufacturers Alliance.