Long adhesive joints in façade applications exposed to wind suction

Abstract

This paper provides an insight into the investigation of long thick-layer adhesive façade joint resistance to negative pressure loads, i.e. wind suction. The real structural response to wind actions was simulated with reference to ETAG 034. Each specimen represented a reference façade section. The experiment focused on four different adhesive systems with flexible high strength 1-K polyurethanes and 1-K modified silyl polymers. Several variants of the test assemblies were tested: 1) a test assembly with an adhesive joint when a) the manufacturers’ application instructions for the system were followed and b) the instructions were violated; 2) a test assembly with a mechanical joint. These variants made it possible to compare the properties of both fastening methods, and moreover, to assess the impact of the mounting tape on the properties of the adhesive joint. The comparison of adhesive joints and a mechanical joint proved the greater structural stiffness and stress resistance of bonded assemblies. Monitoring showed that a local failure of the fastening element between the load-bearing frame and supporting structure caused the failure of the bonded assemblies, whereas the specimen with mechanically attached cladding failed due to pull-through of the fasteners. The average failure load of the bonded assembly was 10.88 kPa. In contrast, the failure load of the segment with mechanical fasteners was 10.12 kPa. Even though the difference in maximum pressure loads was only around 7%, the recorded values clearly demonstrate that the weakest part of the whole façade system is the mechanical joint, not the bonded one. Furthermore, the comparison of the results for segments with and without mounting tape showed that tape can have a major impact on the bond strength, since in case of the test specimens without mounting tape, the recorded failure load was a maximum of 30% higher.