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 , rounding of glass corners , 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.