Developing a Simple Damage Model for the Long-Term Durability of Acrylic Foam Structural Glazing Tape Subject to Sustained Wind Loading

This article presents a simple linear damage accumulation model that may have applicability for predicting damage from sustained winds in double-sided acrylic foam tape used to attach curtain wall glazing panels to buildings. The purpose of this model is to investigate the possible cumulative effects of years of wind-induced stresses that are less than the peak stress expected during a 3-s gust, as specified in current design guidelines established by the structural glazing industry and adopted by the manufacturer of these structural glazing tapes. Several representative wind histories are selected to provide input data for the model. These wind histories provide multiple years of average wind speeds over either 10-min or 1-h recording intervals, depending on the source. Each entry in a wind speed history is converted to stress on the glazing adhesive tape on assumed window dimensions using the standard wind loading design equations of ASCE 7-05. A creep rupture prediction equation, developed from a creep rupture master curve obtained by experimentally evaluating 3M VHB G23F acrylic foam tape, provides the time to failure as a function of applied tensile creep stress. Using a linear damage accumulation model, fractions of life used at each entry are combined into a total percentage of life used. Based on evidence that cyclic loading may be less significant than sustained stress events, the effect of cyclic fatigue was not considered in this study. The model developed does not provide evidence that the industry established design procedure is unsafe using the selected wind speed histories, provided sufficient safety factors are used. The model does suggest, however, that the accumulation of damage from sustained wind speeds, especially winds from storm events, could present a mode of failure that merits examination along with the more traditional peak wind speed design procedure currently in use by the structural glazing industry and employed by the vendor. The approach may have applications for other time-dependent glazing sealants as well.