SSG Design Considerations

According to building codes, curtain wall systems attached to the building structure are deemed “non-structural elements." As with the superstructure of a building, these systems are also susceptible to damage from earthquakes, with glass fallout a life-safety hazard of significant concern. Curtain wall systems are designed around drift-based criteria, and system designers strive to create sys­tems that utilize design elements to: control movements, improve drift capaci­ties, and to minimize damage of the facade systems attached to these structures. Such accommodations can be in the form of: slotted connection holes [8], rounding of glass corners [9], interlocking unitized sub-frames, split mullions, movement accommodating frame-to-slab connections, and adhesively bonded glass and metal (SSG) including a properly selected structural silicone adhesive, which will be discussed more in-depth later.

An example of commonly used system in the Chilean market and in the buildings reviewed in this paper is the split-mullion type and are supported on a slide anchoring system as shown in Figs. 3 and 4. These systems offer move­ment accommodation via physical separation of interlinked components with typical accommodation ranges noted in Fig. 3. When seismic loads impose lat­eral displacement (interstory drifts) to the building, these de-linked components act along with slide-type supports to accommodate the displacements and in­plane rotation of glass relative to the supporting aluminum frame until the ranges are spent. At this point, the displacements will engage the structural seals by inducing in-plane transverse shear deformation with maximum strains occurring at corner locations. It is the corner locations that will be checked for silicone reaction. A more involved discussion involving the calculation of inter­story drift and sealant shear strain is presented later.