In seismic events, glass curtain walls undergo racking deformation, while the flat glass lites do not rack due to their high shear stiffness. If the glass curtain wall is not isolated from the building frame by specifically designed connections that accommodate relative motion, seismic racking motion of the building frame will demand significant resiliency of the sealant that secures the glass to the curtain wall framing. In typical four-sided structural silicone glazing systems used in buildings with unbraced moment frames, the magnitude of seismic racking is likely to stress the sealants significantly beyond the sealant design strength.
In this paper, the extent of the expected seismic racking motion, the behavior of the structural silicone glazing when subjected to the expected racking motion, and the field performance of a building with four-sided structural silicone glazing during the Northridge earthquake are discussed. The details of a curtain wall design concept consisting of shop-glazed subframes connected to the building frame and the connections that accommodate seismic motion of the subframe relative to the building frame is developed. Specific recommendations are made for the design of the four-sided structural silicone glazing systems for seismic loads.