This paper provides the net wind pressures on a series of curved open canopy (i.e. free) roofs. Net wind pressures acting across the roof were obtained by testing two 1/50 scale model configurations in a boundary layer wind tunnel. Design data for such structures are not readily available in codes and standards. The paper determines net pressure coefficients across taps on the top and bottom surfaces of the roofs. Large net negative (outward) and positive (inward) pressures were measured at the leading edges. Net aerodynamic shape factors Cshp,n are given in a form appropriate for the Australian/New Zealand wind loading standard, AS/NZS 1170.2:2021 to obtain loads for the design of cladding and the supporting structure.

The latest revision of AS/NZS 1170.2 incorporates some new research and knowledge on strong winds, climate change, and shape factors for new structures of interest such as solar panels. Unlike most other jurisdictions, Australia and New Zealand covers a vast area of land, a latitude range from 11(degrees) to 47(degrees)S climatic zones from tropical to cold temperate, and virtually every type of extreme wind event. The latter includes gales from synoptic-scale depressions, severe convectively-driven downdrafts from thunderstorms, tropical cyclones, downslope winds, and tornadoes. All except tornadoes are now covered within AS/NZS 1170.2. The paper describes the main features of the 2021 edition with emphasis on the new content, including the changes in the regional boundaries, regional wind speeds, terrain-height, topographic and direction multipliers. A new 'climate change multiplier' has been included, and the gust and turbulence profiles for over-water winds have been revised. Amongst the changes to the provisions for shape factors, values are provided for ground-mounted solar panels, and new data are provided for curved roofs. New methods have been given for dynamic response factors for poles and masts, and advice given for acceleration calculations for high-rise buildings and other dynamically wind-sensitive structures.

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.

Net pressures on roofs and walls of a building are dependent on the internal and external pressure fluctuations. The internal pressure is influenced by the sizes and locations of the openings in the building envelope. The peak net pressure (C proves ) for cladding design on the roof and walls of a building will depend on the internal and p,net external pressure fluctuations and their correlation.External and internal pressure fluctuations and their correlations measured on the roof and wall of a 1:200 scale model nominally permeable building and a building with a wall opening were used derive peak net pressures. The large external suction pressures and the small internal pressures in the permeable building are positively correlated whilst the large external suction pressures and the large positive internal pressures in the building with windward wall opening are negatively correlated. Widely available basic statistical properties of external and internal pressures (i.e. mean, standard deviation, and peak coefficients) and their correlations are applied with the fundamental theory of the covariance integration method (without the need for their time histories) to satisfactorily estimate the peak net design pressure to within 10% of the measured value.

This paper summarises activities in the area of Wind-Structural Engineering in Australia between 2012 and 2021, including the work, carried out for Standards Australia and research at Universities in Australia. The main changes are; the redefinition of wind regions and the recalculation of wind direction multipliers in Section 3, refinement of terrain height, shielding and topographic multipliers in Section 4, inclusion of an open area volume factor for internal pressure and changes to the local pressure factor and area reduction factors in Section 5, new data for along-wind and cross-wind response of slender structures in Section 6, and revised data for curved roofs and new data for open conical roofs and ground mounted solar panel arrays in the Appendices. These revision are based on research carried out in this period.

Recent damage surveys have shown that double-skillion roofhouses, characterised by two monoslope roofslopes with a vertical 'rise' connecting the upper and lower roof slopes, are vulnerable to cladding and structural failures in windstorms. Wind loading Standards such as AS/NZS 1170.2 do not currently provide pressure coefficients for deriving design wind loads specifically for these types of double-skillion roofs. This paper presents a 1/50 scale wind tunnel model study on a typical double-skillion roof house. The study found that the upper roof slope experiences large suction pressures especially near the upwind corner for oblique approach winds. In addition, the lower roof slope and rise are subjected to large positive pressures. The structure (i.e. rafters) near the end-walls also experiences large hold-down loads. Cladding loads and rafter hold-down loads are significantly larger than values obtained from applying data currently available in AS/NZS 1170.2

Net pressures on roofs and walls of buildings are dependent on the internal and external pressure fluctuations. The variation of internal and external pressures are influenced by the size and location of the openings. The correlation of external and internal pressure influences the net pressures acting on cladding on different parts of the roof and walls. The peak internal and peak external pressures do not occur simultaneously, therefore, a reduction can be applied to the peak internal and external pressures to obtain a peak net pressure for cladding design. A 1:200 scale wind tunnel model study was conducted to determine the correlations of external and internal pressures and effective reduction to net pressures (i.e., net pressure factors, ????????) for roof and wall cladding. The results show that external and internal pressures on the windward roof and wall edges are well correlated. The largest ????????,????????????, highest correlation coefficient and the highest ???????? are obtained for different wind directions within 90o ≤ ???? ≤ 135o , where the large openings are on the windward wall. The study also gives net pressure factors ???????? for areas on the roof and wall cladding for nominally sealed buildings and the buildings with a large windward wall opening. These factors indicate that a 5% to 10% reduction to the action combination factor, ???????? specified in AS/NZS 1170.2(2011) is possible for some critical design scenarios.

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.

Batten to rafter connections in light framed timber housing can be vulnerable to wind loading, and failures of these connections are one of the more common failure modes seen in post windstorm damage surveys. Such failures often occur in a progressive or cascading manner resulting in the loss of a large section of the roof envelope. These progressive failures of batten to rafter connections are a complex process influenced by the pressure fluctuations on the roof surface, the response of individual connections and the behaviour of the structural system as a whole. This study presents a method for examining load redistribution and progressive failure behaviour of batten to rafter connections in light framed structures. Nonlinear time history analyses were performed using a finite element model using fluctuating pressures determined from a wind tunnel study and connection properties determined from laboratory testing of connections under dynamic loads.

Vulnerability models for housing during extreme wind events are a critical part of modern catastrophe modelling used to inform insurance pricing, policy-making, emergency management, etc. Historically, the most robust vulnerability model development has taken place in the US. However, since structural systems in the US differ significantly, it is important that Australia-specific models are available and fully described in the literature. Development in Australia has continuously progressed since early works of the 1970s, although much of the research exists in unpublished format. Models from unpublished studies have been used broadly in academia, insurance and by policymakers, in many cases without a clear understanding of underlying assumptions and limitations. The aim of this paper is to provide a review and clarification of these models and introduce the Vulnerability and Adaption to Wind Simulation (VAWS) model, which takes an engineering-based approach. An overview of VAWS program logic and engineering assumptions is presented in addition to a comparison of outputs for one cyclonic region house type with existing models and insurance claims data. For the housing style considered, results suggest that VAWS can provide a better estimate of vulnerability than existing Australian models and those from abroad, not specific to Australian construction.

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.

The net wind pressure on roof cladding of metal clad buildings are critical for structural design. Large openings on the windward wall generate large positive internal pressure, which in combination with high external suction pressure produces large net negative pressure on the roof. Wind tunnel studies conducted on a 1:200 scale industrial building model and analytical methods were used to analyze combination effects of internal and external pressures on roof cladding. AS/NZS 1170.2 gives conservative net pressures on the windward roof edge of buildings, for quartering approach wind. The combination factor \(\left( {f_{C} = C_{{\check{p},net}} /\left( {C_{{\check{p}e}} - C_{{\hat{p}i}} } \right)} \right)\) varies depending on location of the cladding element and position and type of opening(s) in the envelope. The calculated \(f_{C}\) factors are 5% less than the combination factor in the AS/NZS 1170.2 for roof cladding of nominally sealed buildings while it is 5–10% less than the building with the large opening. Helmholtz resonance occurs in the building with large opening and internal pressure influences energy contained in the net pressure at the Helmholtz frequency. External suction pressures on windward roof edge and positive internal pressures in the building with large windward wall opening are negatively correlated whilst of external and internal pressures are positively correlated, in the nominally sealed building.

This paper describes some features of public cyclone shelter design for tropical North Queensland Australia. These buildings are required to resist very high wind and windborne-debris speeds, in the context of apparently increasing numbers of very severe tropical cyclones affecting the Queensland coastline. An interesting aspect of the standard shelter design is the corner shaping and venting of the roof and walls, which are shown to significantly reduce the local wind pressures.

Net wind pressures acting across solar panels were obtained by testing 1/20 scale models in a range of typical array configurations in the wind tunnel. This paper presents data for a typical panel array configuration inclined at alpha = 20 degrees. Large net negative (upward) pressures were measured on the panels at the leading edges for wind blowing towards the bottom surface of the sloping panels. Shielding from upwind arrays was negligible. Large net positive (downward) pressures were measured on the panels at the bottom leading edge for wind blowing towards the top surface of the sloping panels. Aerodynamic shape factors C-shp on the panels and arrays are given in a form that has been proposed in the revision of the Australian/New Zealand wind loading standard AS/NZS 1170.2.

Residential house structures in Australia are timber-framed construction and their roof connections are the most vulnerable components to windstorms. The failure or partial failure of inter-component connections within the roofing system, creates a change in the load path and load transfer from roof to wall. A series of finite element models were developed to derive the vertical reaction influence coefficients of roof to wall connection (RWC) and load sharing of roof structural system. Hold-down forces of RWCs were derived by using vertical reaction influence coefficient and wind tunnel model test data. The results show when the single rafter RWCs failed in the roof, the hold-down forces of adjacent rater’ RWCs will increased by about 55%. Overall outcomes of this research are being used as part of the BNHZ-CRC projects for retrofitting the roof structure and to develop vulnerability models for the houses.

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.

Investigations of damage to buildings and analysis of insurance claims data following severe wind events have shown that there are still problems with the performance of contemporary engineered buildings. Significant financial loss in terms of cost of rebuilding or repair, and loss of functionality has been documented following recent severe Tropical Cyclones Yasi, Marcia, Olwyn and Debbie. The wind speeds in these events were less than the design level wind speed for buildings in the affected regions. This paper discusses damage to a range of contemporary engineered buildings ranging from luxury strata to single residential properties; and commercial, public and post-disaster buildings. In some cases, structural details failed leading to loss of large parts of the building envelope. In other cases, costly insurance claims arose from wind-driven water entering buildings through flashings, doors and windows, even when there was no damage to the building envelope. From the damage investigations and claims data analysis, several recommendations are detailed. These include; appropriate design and detailing for strength of connections for verandahs, awnings and carports; maintenance of components or durability design for components not easily accessible after construction, minimum standards for fixing flashings, etc.

•Extreme wind is a major source of loss to residential housing.•Fragility analysis expresses roof damage as a function of wind speed.•Spatial reliability analysis models damage progression.•Annual risk is up to 0.3% of house replacement value.•Climate changes may increase expected losses by up to 18%.

Batten to rafter connections in light framed housing can be vulnerable to progressive or cascading failures where a localised failure can cause the loss of a large section of the roof envelope. The synchrony of loads at neighbouring connections may affect the initiation of such failures. A 1/50 length scale wind tunnel model study was performed on a gable roof house to record spatial and temporal pressure fluctuations on the roof surface and data were studied to determine the flow separation mechanisms causing different loading patterns on batten to rafter connections. The cross correlation between load time histories was used to give a measure of synchrony between loads experienced at neighbouring connections and indicate the direction that fluctuations move across the roof. Orthogonal wind directions result in 2-dimensional flow separation that produce more synchronous loads at batten to rafter connections than cornering wind directions, where conical vortices produce high uplift forces on connections. The patterns of loading and their correlations give a means of identifying which parts of the roof and which approach wind directions may result in the initiation of a progressive failure of batten to rafter connections.

The roof is the part that experiences the largest wind load and is usually the most vulnerable part of a house. However, data on how the wind loads are transferred through the roof structure are scarce. The fluctuating nature and variable spatial distribution of wind loads combined with the structural response can cause significant challenges for assessing the distribution or sharing of loads in a roof. Such studies are required to obtain more reliable estimates on vulnerability assessment to windstorms. This paper describes the transmission of wind loads from the pressure on the cladding through the cladding-to-batten connections to the batten-to-truss connections on a roofing system typical of that in many contemporary houses constructed in cyclonic regions of Australia. The study found that the use of normal design practices can significantly underestimate connection loads when highly correlated large-scale wind pressures act on these roof systems.