This work addresses the typically overlooked topic of in-depth facade – structure movement interaction analysis. The findings of this analysis are directly exposing the limitations, and, in some cases, potentially unsafe design of many systemised and bespoke structurally glazed UCW systems. When a typical row of panels is subject to floor slab movement due to live load, a phenomenon known as “racking” occurs and most systems rely on panel-to-panel engagement and contact. This behaviour coupled with fashionably large vision glass IGUs, leads to a compatibility issue relating to the glass effectively restraining the unitised frame via the stiffness of the sealant. While this issue is somewhat explored for instantaneous live load movements, it is rarely acknowledged that a component of this live load acts permanently and for the lifespan of the façade in most building types, the so called quasi-permanent component of live load. Currently there is no design guidance in the industry for examining this behaviour and designing effectively for it. The lack of codified methods for sealant design which is currently done on a presumptive conservative methodology stated in ETAG 002 necessitates a more sophisticated FEA analysis under long term actions to be carried out. The results reveal that a large majority of SG UCW facades built and currently in construction would have under-dimensioned profiles and sealant joints incapable of limiting the permanent sealant stresses under long-term panel racking under the manufacturer stated limits.
An inconvenient analysis: SG Unitised Systems behaviour
Company: Define Engineers ltd, London, United Kingdom. Imperial College London, London, United Kingdom
About the speaker:
Vlad is a specialist structural engineer and founding director of Define Engineers. He has a strong analytical background and over 15 years of broad experience in traditional construction, complex structures and innovative materials. Regarded as an influential figure in the special structures field, he has designed and delivered many landmark and award-winning projects world-wide. Vlad enjoys collaborating on highly challenging briefs which involve first principle thinking combined with rigorous analytical approach.