Compared to
traditional steel and aluminum assemblies, this new generation of steel frames
provides certain basic design benefits such as narrower frames; sharp edges
versus rounded profiles; corner joints without any visible weld beads or
fasteners; and flexibility to use back mullions of different shapes and sizes.
Since framing establishes the base for a curtain wall assembly’s performance,
systems employing this new forming methodology can effectively satisfy demanding
design and performance criteria. Moreover, cold roll-formed and laser-welded
steel bar processes can capitalize on steel’s obvious strength over more
conventional materials like aluminum. Steel has a modulus of elasticity nearly
three times of aluminum by applying new forming methodologies, this can
translate into a smaller system frame profile and component parts than aluminum
without decreasing end-use performance. Consider long steel or extruded
aluminum mullion with the same cross-sectional properties, using as the design
load discounting allowable deflection limits momentarily. An aluminum mullion
deflects whereas a steel mullion deflects allows the designer to do one, or all
of the following when using steel as the primary framing material.
Using a smaller
system shapes while meeting the same deflection criteria, thus translating to
larger, uninterrupted views of the outside environment and greater illuminance
for interior occupied spaces to support larger lite of glass or other glazing
infills than the aluminum cousins or the span larger heights without the need
for reinforcing or more frequent connections to the steel bar in building
structure. Despite the many benefits associated with these new steel bar
forming methodologies, myths continue to circulate around steel’s limitations
in curtain wall systems. These steel bar framing processes are well understood
and used but they are still new to other markets in accounting for much of this
confusion. To help set the record straight, it will address three relevant
inaccuracies as they relate to laden winters, subarctic temperatures, and in
energy and environmental design goals. Among the most common misconceptions
about steel is the carbon alloy is unsuitable for use as a primary framing
material due to corrosion because early steel curtain walls were vulnerable to
rust, and the industry turned to more corrosion-resistant materials, such as
aluminum.
In a country largely
subjected to freezing winters with heavy snowfall, those in the design-build sector
are rightfully wary of building materials that cannot stand up to moisture and
air, two of the main catalysts for corrosion. They have led the way in
developing systems that eliminate much of the water and steel bar contact in
glazing systems is typically present in the glazing pockets, where the glass is
captured along its edges, to hold it onto the framing. The means of capture
employs gaskets since metal to glass contact would not create the necessary air
and water seals required by the specification. Pioneering a solution took the
gasket at the face of the primary framing member, which forms the interior
portion of the glazing pocket, and entirely covered the face of that steel with
the gasket, completely removing any possibility of water coming into contact
with the steel. Water from other portions of the façade, such as the perimeter
interface with surrounding construction or from the surrounding construction
itself, is precluded by intelligent detailing and execution of those conditions
to the governing principle is water should not come in contact with the steel,
and the systems themselves address water isolation from steel internally.
