Design optimisation of arch-supported membrane canopies utilising CFD technology

Abstract

Optimization of the profile shape of a free roof canopy determines the relationship between height to span (H/S) ratio and cost relating to tonnage of structural steel. A free roof canopy is a compromise between form, function and cost. The form of a free roof canopy is determined by utilizing four basic shapes Barrel Vault, High Point (Conic), Hypar, Saddle and variations/combinations of these forms/shapes. This research thesis investigates the relationship between the H/S ratios of the Barrel Vault free roof profile. Within building design, tensile membrane canopies are becoming widely accepted as an alternative to conventional building roof materials. In European situations, wind and snow are the two main load cases applied to a canopy during analysis. In Australia wind is the main load case as very few projects are constructed within the alpine regions. Water ponding on an impervious canopy is also a major consideration, therefore the profile of the fabric roof canopy must be able to shed water during heavy rainfall which is often accompanied by wind. The free form nature of a tensile membrane canopy and the niche position they have in the construction industry, leads to the issue of lack of relevant data relating to the wind action on the canopy. For large free form canopies wind tunnel tests are conducted to determine relative Cp values. On small scale projects wind tunnel tests are not feasible due to time constraints and the related expense. Due to advances in software technology Computational Fluid Dynamics (CFD) is a viable aid in the design process of tensile membrane structures. CFD is able to quickly visualize the wind effect and wind turbulence created by the roof profile. Pressure mapping from the CFD to the FEA software begins the optimization process of a free roof canopy thus determining the relationship between Height to Span (H/S) ratio and cost (structural support-tonnage of steel) that influences the design of the final project. An increase in the H/S ratio may positively influence the form and aesthetic appeal of the structure while not significantly increasing the cost - tonnage of steel. The aim of the research is to provide designers with data which will be of assistance during the design phase of a barrel vault tensile membrane project.