Dormant Curtain Wall Anchors: Relative Stiffness Oversights

The primary author has investigated a wide variety of curtain walls exhibiting many types of distress. As part of these investigations, original and remedial designs were reviewed to assess the structural adequacy of the existing or supplemental anchorages. The designs often included curtain wall components attached by multiple anchorages. In an effort to simplify the structural analyses of these anchorages, the relative stiffness between fastened curtain wall components was occasionally neglected so that the applied wind load could be distributed uniformly to the anchors. As a result of this design simplification, some existing or supplemental anchorages would be relatively dormant under applied loads, while others would be overstressed. To illustrate the consequence of neglecting relative stiffness in the analyses of curtain wall anchorages, the authors will present three short case histories involving a variety of curtain wall types in different areas and territories of the United States. The case histories include a typhoon-damaged hotel with an exterior insulation and finish system (EIFS) located on a Pacific island, a high-rise office structure with failed granite panel anchors located in the Midwest, and a high-rise office structure with a planned aluminum spandrel overcladding program located in the West.