Point-Supported Structural Glass Facades: Fins, Fittings, and Frameless Glazing
A conventional curtain wall, covered in our article on curtain wall structural design, still relies on an aluminum mullion and transom grid to carry wind load back to the building frame, with glass sitting passively inside that grid. A frameless or point-supported glass facade removes that grid almost entirely and asks the glass itself, along with a small number of discrete fittings, to do the structural work − a fundamentally different design problem because glass is a brittle material with almost no ductility, and a structural system built from it has to compensate for that with lamination, redundancy, and very conservative stress limits rather than the yielding reserve steel or aluminum provide.
Glass Fins as Structural Members
Where a frameless wall needs a stiffening member to span between floors and resist wind load, that role is often filled by a glass fin: a vertical glass blade set perpendicular to the facade plane and bonded or clamped to the glazing it supports. A glass fin is designed much like a slender beam − sized for bending stress and, especially at taller spans, for out-of-plane buckling − except the material's brittleness means the working stress limits are set far below the glass's actual breaking strength, and fins are almost always built from laminated glass (two or more glass plies bonded with an interlayer) specifically so that if one ply cracks, the interlayer holds the pieces in place and the remaining plies can still carry load until the panel is replaced. A monolithic, non-laminated glass fin has no such fallback, which is why building codes and industry standards for structural glass, including load and safety-factor guidance published as ASTM E1300, effectively steer designers away from single-ply fins in most structural applications.
Laminated glass also changes how a fin or panel actually behaves under sustained versus short-term load, because the plastic interlayer between plies stiffens under brief loading (like a wind gust) but creeps and softens under sustained loading (like the panel's own long-term dead weight), so the same laminated section is analyzed with two different effective stiffness values depending on load duration rather than one fixed property.
Point Fixings and Load Transfer
Instead of a continuous frame edge, point-supported glass is held by discrete fittings − often called spider fittings for the multi-arm steel castings that grip several panel corners at once − bolted through a hole drilled in the glass itself. Every one of those bolt holes is a stress concentration in a brittle material, so the glass around each fitting is typically tempered or heat-strengthened specifically to raise its tolerance for that local stress, and the fitting itself is detailed with a compressible bushing or sleeve so the steel fitting never bears directly on the glass edge inside the hole, which would otherwise create a hard contact point prone to chipping or cracking under thermal movement.
Because each point fitting concentrates the panel's entire wind and self-weight reaction into a handful of small contact areas, rather than distributing it along a continuous frame edge the way a standard curtain wall does, deflection and stress checks at point-supported panels are noticeably more sensitive to fabrication tolerance − a hole drilled slightly off-center, or a fitting installed with unintended eccentricity, changes the local stress distribution more than an equivalent tolerance error would on a framed system, covered generally in our article on deflection control and serviceability.
Redundancy and Fallback Behavior
Because a point-supported facade has so few structural elements compared to a framed curtain wall, redundancy has to be designed in deliberately rather than assumed: laminated interlayers that hold cracked glass in place, fittings sized to continue carrying load even if one ply of a laminated pane fails, and cable or rod bracing systems (used on some point-supported walls instead of glass fins) detailed so that a single cable's loss does not bring down the panel it supports. None of this is exotic engineering, but it is engineering that a standard framed curtain wall rarely has to think through in the same detail, since the frame itself already provides the redundancy that a frameless system has to build in another way.