Glass Canopy anchors are required to do a lot more work than typical anchors for skylights and cladding systems. This is due to the need for them to resist:
- The deadload of the canopy
- The torsion created by the cantilever of the canopy
- The uplift forces of windload
- The deadload of projected snow and ice accumulation
- For these reasons, structural engineering calculations for canopies are often much more involved than those for other glazing systems
The strength required for a glass canopy anchor can suggest anchor dimensions that are at odds with the design requirements of the canopy itself. The opportunity to conceal the anchoring system is often based on whether the project is new construction or a remodel.
A preferred anchoring design is to weld or mechanically connect the canopy structure back to building steel which has been designed to support that related forces. In this case, outriggers or tubular framing can be anchored in an unseen way, for the cleanest sightlines. Whenever possible, a concealed anchoring system that is directly connected to the steel or concrete structure of the building (or door portal) will provide the purest design options without additional supports.
Outrigger tieback rods may be required when the canopy can only be face mounted to the building cladding, and the cantilever of the canopy would overwhelm the strength of a bolted mounting plate. While drawings often call out steel or stainless cables for tiebacks, actual rods are required, since cables would not resist the uplift of wind pressures.
Knife plate anchors designed to fit in between vertical curtain wall mullions, are another discrete design choice. These anchors require complete coordination between the canopy designer, curtain wall manufacturer, and structural steel supplier.
In all cases, successful glass canopy design and installation is dependent upon excellent coordination and communication between design and installation trades.