The wind induced internal pressure in a typical, porous steel-clad shed is dependent on the dis-tribution 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.

Windstorm damage surveys highlight that the discontinuity in load resistance and transfer of connections in timber-framed housing can lead to total failure of the roof structure. Field surveys of timber-framed houses under construction in Australia also indicated that, for a typical roof configuration, at least three of its six or more roof trusses had common construction defects (i.e. missing nails) in roof to wall connections (RWCs). It is expected that these construction defects will reduce the capacity and stiffness of the connections, creating variations in the wind load sharing, load transfer and the forces at the roof to wall connection of timber-framed houses. This study develops finite element models coupled with wind tunnel model tests of timber-framed houses to evaluate the load sharing and the hold-down force when there are construction defects and stiffness reduction on the RWCs. Both contemporary nail plate truss roofs and traditional (pre-1980s) pitch-framed hip roofs commonly used in Australia were modelled and analysed. The results show that when subjected to windstorms the contemporary houses possess higher load sharing capacity and lead to significantly improved performance than the pitch-framed hip roof houses. Construction defects and stiffness reduction on the RWC of a single truss/rafter can create significant variation in load sharing, and failure of a truss/rafter results in a 55% increase of the hold-down forces of adjacent trusses, leading to a housing structure vulnerable to windstorms. The outcomes of this research provide better understanding of load sharing and can be used as a basis for developing vulnerability models of contemporary and traditional houses to windstorms.

Roof to wall connections (RWCs) play a major role in wind load sharing and load transfer of timber-framed houses. The lack of coherence in the load sharing and load transfer can cause premature failure of timber-framed houses. Thus, it is essential to provide RWCs with adequate strength and stiffness, to ensure the dynamic roof wind loads are adequately shared and transferred through the structural system to the foundations. Typical construction defects in RWCs (i.e. missing nails) reduce the stiffness of the RWCs, introducing discontinuities in load paths, contributing to total roof failure under windstorms. This study combines realistic spatially and temporally varying wind loads, captured from model-scale wind tunnel-studies, with a validated finite element model of the roof structure, that accurately describes the load sharing through the structural system and evaluate the effect of RWC stiffness variations and realistic wind loading variation on the load sharing and hold-down forces of Australian contemporary timber-framed houses. The combined effect of RWC stiffness variations and realistic wind loading variation are compared to the traditional design method approach (i.e. tributary area method and use of simplified design roof pressures from wind loading standard AS/NZS 1170.2 (2011)). Results show that the maximum RWC hold-down force from AS/NZS 1170.2 (2011) is about 10% greater relative than the maximum RWC hold-down force from realistic dynamic wind loads, and overestimates wind loads for most wind angles. The maximum RWC hold-down force derived by the load sharing method with defective connections (i.e. single and double nails missed on the RWCs), induced hold-down forces 10% higher than that of the traditional method at neighbouring RWCs. Further, hold-down force variation between traditional and load sharing methods can increase up to 50% in a real house roof structure, as the stiffness of their RWCs vary throughout the system due to the material non-linearity and construction defects/human errors.

Internal pressures contribute to a significant proportion of the net pressure across a building envelope, which needs to be accurately defined in wind loading standards to optimize structural design. Current quasi-steady criteria for internal pressures in AS/NZS1170.2 [11] is dependent on the ratio of open area on the windward wall to leeward and sidewalls, with no consideration of dynamic (i.e. inertial and damping) effects. This paper shows that the internal to external pressure fluctuation relationship is a function of the opening area to volume parameter, \(S* = \left( {A^{3/2} /V} \right)\left( {a_{s} /\overline{U}_{h}^{2} } \right)\) and opening area to integral length scale of turbulence parameter, \(\Phi_{5} = \left( {\lambda_{u} /\sqrt A } \right)\). Simple quasi-steady analysis used in AS/NZS1170.2 [11] suggests internal pressure should be equal to the external pressure applied to the opening, however, results here show Cases where peak internal pressures are greater than, equal to and less than the peak external pressure. This is caused by internal pressure resonance and/or damping shown to be a function of S* and Φ5.

A single opening on the windward wall which generates large internal pressures in a building often defines the critical wind loading structural design criterion. This paper presents internal pressure fluctuations in a sealed Full-Scale Test Enclosure (FSTE) for a range of single windward wall opening configurations induced by atmospheric wind flow, to assess the influence opening size (i.e. S-star = (A(3/2)/V)(a(s)/(U) over bar (h))(2)) has on the internal pressure. Damped Helmholtz resonance was observed for S-star > 0.88, with peak and standard deviation internal pressures being about 5% higher than the external pressures when S-star > 1.9. Internal pressure fluctuations are attenuated when S-star < 0.75. The inertial coefficient C-I is between 1.3 and 1.5 and the loss coefficient CL increases with increasing opening area (0.88 < S-star < 5.8) between 10 and 20. These parameters have a significant influence on the internal pressure fluctuations, and this controlled full-scale study carried out for the first time provides data for validating analytical and model-scale studies on internal pressure fluctuations in buildings.

Full-scale tests were carried out on a part of representative brick veneer contemporary house to assess the loading effects on roof to wall connections and load sharing. Tests were carried out at each stage of construction: bare frame followed by the installation of roof battens and cladding, wall lining, ceiling, etc. These construction stages were used to assess the contribution of the structural and lining (i.e. ceiling, ceiling cornice and wall lining) elements to the load sharing and response of the timber-framed house structure to wind loading. Results of the full-scale test show that the vertical reaction force at the loaded truss support was reduced by about 20% when the lining elements were added to the system with structural elements (i.e. truss, batten and roof cladding). The vertical load sharing of the timber framed house through the roof to wall connection (RWC) depends on the stiffness of the RWC and the truss location (i.e. whether located at the end or middle). The contribution of the lining elements to the vertical load sharing is about 15-20%. The lateral load resistance of RWCs significantly increased, when ceiling, ceiling cornice and wall lining were added to the structural system. The outcome of this study can be used to assess the structural response and vulnerability of these houses to windstorms. (C) 2016 Elsevier Ltd. All rights reserved.

Design pressures given in wind loading standards are based on wind tunnel studies conducted during the 1970s to 90s on rectangular hip and gable roofs. However, most contemporary houses have complex hip-roof geometries with a range of plan footprints. Wind tunnel model studies were carried out on representative one-and two-storey houses to determine cladding design and truss hold-down loads. These loads were compared to design loads determined from wind loading standards AS/NZS 1170.2 and AS 4055. AS 4055 gave conservative design loads in most situations, and AS/NZS 1170.2 underestimated the loads near the windward edges and ridge on the roof. AS/NZS 1170.2 does give satisfactory design loads for wall cladding and truss hold down.