Structural Systems
Ultimately, structural glass facades are as much about the expression of elegant and minimalist structural systems as they are about facade transparency. The facades completed to date are easily categorized by the structural system types used to support them.
However, a review of the completed projects representative of each system type will reveal a remarkable diversity of application. Enclos has the capability to develop any variation of these system types in response to specific project requirements.
Strongback Systems
Strongback systems comprise a remarkably diverse range of novel structural solutions in facade applications. The structural systems are built up from structural sections capable of accommodating the required span. These systems can include both vertical and horizontal structural components. Sometimes verticals are used with no horizontals. Conversely, an interesting variation of this system type eliminates the vertical mullion, with horizontal components suspended from overhead cables and fixed to anchoring building structure at their ends. Strongback systems also include hierarchical structural frames and braced frames
Truss Systems
Truss systems employ a planar truss design, often in a hierarchical system that may combine other element types including tension components. Truss designs vary widely, with an emphasis on fine detailing and craftsmanship. They often involve complex steel fabrications, frequently manufactured to Architecturally Exposed Structural Steel (AESS) standards. Rod or cable elements may be incorporated into the truss design, and lateral tensile systems are often used to stabilize the facade structure. Simple truss elements are often bordered by one or two cable trusses in a repeating pattern as a means to lighten the structural profile of the facade.
Cable Trusses
One type of truss system utilizes a minimalist structural form called a cable truss. While cable trusses can vary widely in both truss design and configuration with vertical, overhead, vaulted and domed forms easily achieved, the trusses themselves are most often characterized by spreader strut elements representing the only compression members in the structural system. As with cable nets, these systems rely on the pre-tensioning of truss elements to provide stability, and thus benefit significantly from the early involvement of the facade design/build team.
Grid Shells
Grid shell structural systems are another means to minimize the visual mass of structure. Configurations can be vaulted, domed and double-curved. Systems can be welded, bolt-up, or some combination of each. Grid shell structures with integrated cable bracing can produce a highly efficient structure with a refined aesthetic. Cable prestress is required on such systems. Grid shells can be used in vertical and overhead applications, as well as to form complete building enclosures.
Cable Nets
Frei Otto developed and popularized cable nets as a structural system in the 1960s and 70s. Architect Helmut Jahn with engineering firm Schlaich Bergermann applied the technology in a most innovative manner in 1992 as a flat cable net supported glass facade for the Kempinski Hotel in Munich, fueling widespread interest in this structural form in glass facade applications. Cable nets represent the ultimate in elegant minimalist structural systems and can provide optimum transparency when the effect of a sheer glass membrane is desired. The glass is supported by a net geometry of pre-tensioned cables. Designs can be flat, or the net can be pulled into double-curvature. A clamping component locks the cables together at their vertices and fixes the glass to the net. Large pre-stress loads in the net structures require the early involvement of the facade design/ build team with the building engineer.
Glass Fin Systems
This is the earliest form of structural glass facade dating back to the 1950s and the French Hahn system used at the Maison de la Radio in Paris in 1953. Here 2-story glass plates were suspended and laterally stiffened by the use of glass fins set perpendicular to the plates at the vertical joints between them. This technology was popularized by the Willis Faber & Dumas Building, Ipswich, England circa 1972. In this curved facade designed by Foster Associates, multiple plates of reflective glass are suspended to provide one of the first examples of an entire building facade being skinned by frameless glass. This project inspired a diffusion of glass fin technology in numerous applications throughout Europe and America starting in the 1970s and continuing today. Glass fin-supported facades still represent one of the most transparent forms of structural glass facades and an economical solution (especially at lower spans).
Glass Structures
Glass is increasingly being explored as a structural element. Glass stair treads and landings have become commonplace, and the material has even seen limited use in column and beam applications. Apple stores have explored this capacity to spectacular effect.
One of the hottest areas of glass development is in glass beams. These typically take the form of multi-ply laminates of heat-treated glass, and special structural laminates are sometimes used. The analysis and connection detailing of these components requires particular expertise. Enclos completed what is believed to be the largest single application of structural glass with the Howard Hughes Medical Center, which included the extensive use of glass beams.
