Permeability and wind induced internal pressures in steel sheds

Abstract

The wind induced internal pressure in a typical, porous steel-clad shed is dependent on the distribution of external pressures and the permeability across the envelope. The permeability of the envelope is dependent on the construction methods and wall fixtures (i.e. windows, roller doors etc). The permeability of walls range between 0.5% and 1.5%, with the surfaces that have roller doors having more leakage.Internal pressure fluctuations in these porous buildings are generally much lower than the external pressure fluctuations. The magnitude of the internal pressure is significantly influenced by the actual distribution of permeability and the magnitude of the external pressures on the windward and leeward surfaces.Positive internal pressures are generated in cases where the ratio of the windward/leeward wall opening ratio exceeds 0.5, in contradiction to recommended negative pressures given in AS/NZS 1170.2:2021. This is mainly due to the higher magnitude of positive external windward wall pressure compared to the external suction pressures on the other walls. Such a scenario could be the governing design criterion for the cladding and the structural system of these types of buildings.