Spandrel Glass Design

Currently, most spandrel glass in commercial curtain walls comprises insulating glass fabricated using an interior heat strengthened glass lite that has a full flood coating of opaque ceramic enamel frit. Recently, numerous thermally induced fractures have been documented on the lite with ceramic enamel frit. In addition, investigation has indicated fracture origins were located at the heat strengthened glass surface to which the flood coat had been applied. This indicates the ceramic enamel frit significantly reduces the magnitude of stress at which glass fracture initiates, i.e., full flood ceramic enamel frit weakens the heat strengthened glass. This paper investigates approaches to the design of spandrel glass through determination of load resistance. Specifically, the cases investigated include (a) use of full flood ceramic enamel frit with a reduction factor applied to the load resistance of the lite that has the full flood ceramic enamel frit application, (b) use of laminated interior lites fabricated with high performance opaque interlayers, and (c) use of an opaque silicone coating of appropriate color on the interior lite. The results indicate that any one of these approaches will produce adequate designs to resist wind loads although two of the methods result in larger values of load resistance. The final design selection will be dictated by economics which this discussion does not address.