The Structural Power of Glass (Continued from p. 38 of the October 2009 issue of BD+C)
Regarding curtain wall anchoring systems, Petermann explains that “each bolt used increases the likelihood of thermal bridging through the thermal break, thereby reducing energy performance. However, limiting the number of fasteners may impact structural capacity.” One way to overcome this problem, according to Petermann and Bostrom, is to use fasteners that don’t span the thermal barrier. However, such fasteners can be more costly to install than conventional fasteners.
Framing materials can also be affected. For example, while aluminum and steel offer good load-bearing capabilities, thermal breaks for better thermal performance can somewhat reduce the structural capacity of the frames, note Petermann and Bostrom. Consequently, some applications may call for non-metal frame materials, such as fiberglass or reinforced vinyl, which offer lower thermal conductivity levels.
GLASS CURTAIN WALLS
With proper design to guard against thermal bridging, the unique properties of glass have lent the material to the development of glass curtain walls, which offer transparency, aesthetics, and structural and thermal performance benefits. Whether stick-built on site or unitized through shop prefabrication, curtain wall systems offer specifiers the choice of numerous interior- and exterior-glazed options. In some cases, the choice is dictated by accessibility to the site. For example, according to Vigener and Brown, high-rise construction tends to work best with interior glazing because of the improved logistics and access for replacing or repairing glass.