Preliminary Evaluation of the TSSA Film Adhesive With the Aim of Developing Static and Dynamic Design Stress Values
Performance specifications for structural glazing, such as ASTM C1184-05 Standard Specification for Structural Silicone Sealants , ETAG 002 Guideline for European Technical Approval for Structural Sealant Glazing Systems , or EN 15434:2006+ A1:2010 Glass in building-Product standard for structural and/or ultraviolet resistant sealant (for use with structural sealant glazing and/or insulating glass units with exposed seals) , were developed for linear bonded bearings and with cold and liquid applied, chemically curing elastomeric structural silicone sealants in mind. While applications of the structural silicone film adhesive are not directly covered by these standards, based on their internal evaluations, the authors expect the structural silicone film adhesive to pass the durability aspects of these standards without problems, as similar exposures have been carried out internally.
Adhesives used in structural bonding in buildings are required to carry certain design loads in their resistance to fracture and meet certain serviceability limit states which define functional performance and behavior under loads. Since the design strengths of the individual building components contribute to the overall strength limit state of the building, which is important to the safety of the structure, building codes and requirement standards traditionally focus on this aspect. While there are well-accepted dynamic and static design strengths for standard structural silicone sealants arrived at by industry consensus based on past performance of structural glazing facades, currently no widely accepted procedure or framework exists for the derivation of long-term design strengths of novel structural adhesives.
Therefore, this paper attempts to contribute towards such procedure by investigating the specific performance and durability characteristics of the novel structural silicone film adhesive. These results could provide insights into the robustness of the structural silicone tape adhesive for glazing applications and lead to an improved understanding for the design process.
Long-term static load resistance (creep rupture) studies have been used in the past in establishing both the short-term dynamic and the long-term static
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maximum design strengths of adhesive systems . While such studies are useful in establishing long-term performance, they do not reflect the wide range of loading rates as experienced by the adhesive in the field when subjected to wind loading and; therefore, are less suitable for establishing short-term dynamic design loads. Furthermore, creep rupture failure tests take the specimens to destruction and the time to failure is affected by micro – or macroscopic defects, such as cracks and voids, in the adhesive layer. A major disadvantage with this approach is the large variation associated with time-to-failure measurements. Therefore, creep rupture tests, especially those carried out to determine short-term design strength, require a large number of specimens and the use of suitable statistics, such as the use of Weibull distributions , in order to obtain meaningful information from the scatter of failure times using probabilistic modeling. Using nondestructive tests with a load limit criterion that correlates with the ultimate strength of the joint, as described below; therefore may be a more desirable approach in deriving the dynamic design strength value.