J.D. Ginger

Internal pressures in a low-rise full-scale building

Theoretical analysis, numerical simulation and full-scale measurements were carried out to investigate internal pressures at the WERFL low-rise full-scale test building at Texas Tech. The mean and fluctuating internal pressure coefficients are small in the nominally sealed building; and increase with increasing windward/leeward open-area ratio. The effects of building flexibility on the internal pressure fluctuations are accounted for, in this study. Internal pressure fluctuations above a characteristic frequency are attenuated in the nominally sealed building. The internal pressure energy is increased close to the Helmholtz frequency, in the building with a single-dominant opening.

Tropical Cyclone Larry: Estimation of Wind Field and Assessment of Building Damage

Summary Tropical Cyclone Larry made landfall on 20 March 2006 near Innisfail, causing significant damage to buildings in the surrounding areas. This paper is based on the field survey and assessment of the performance of buildings, which experienced severe winds in the Innisfail region during Tropical Cyclone Larry. The peak gust wind speeds in the study area are estimated at 50 to 65 m/s, which is less than the region’s current design wind speed. Damage to the housing stock was estimated at about 20% (not including water ingress). Contemporary housing fared considerably better than older housing, reflecting marked improvement of construction detailing and better structural condition, and satisfactory performance of relevant standards. Failure of roller doors, loss of roof battens when fastened to rafters with one or two nails, and loss of rafters or trusses when anchored to top plates with skew nails only, were common. Structural component failures of under-designed cold-formed steel sheds and garages were also widespread. Construction details used in houses on or near hill-tops need to reflect the higher wind speed caused by topographic effects.

Net pressures on a low-rise full-scale building

Abstract The quasi-steady design approach is used by many wind loading standards such as AS1170.2 1989, to determine the design net (i.e. external–internal) pressures on cladding elements and fixtures of low-rise buildings. External and internal pressures measured on the WERFL test building at Texas Tech were used to determine the net pressures at selected points, representative of cladding elements and fixtures on the walls and roof of the building, when nominally sealed and when containing large openings. The mean and fluctuating internal pressures were small in the nominally sealed building and the net pressures derived from AS1170.2 were conservative. In the case of the building with a dominant windward opening, the internal pressure closely follows the external pressure at the opening, and the net pressures derived from AS1170.2 were smaller compared to the measured pressures in some areas near the roof windward edge.

Wind loads on planar canopy roofs, Part 2: fluctuating pressure distributions and correlations

Fluctuating pressure distributions on planar canopy roofs are presented based 1:100 scale wind tunnel measurements obtained in a simulated suburban atmospheric boundary layer. For a range of roof pitch angles and wind directions, point and area-averaged pressure measurements were obtained with the worst loads experienced adjacent to lines of flow separation. For two particular roof pitches the cross correlations of area-averaged pressures were obtained and the covariance integration technique used to estimate the total fluctuating loads on the roof for a range of wind directions. Significant reductions in overall uplift and racking loads, were obtained using this method when compared with the traditional quasi-steady approach. This is because the partial correlation of fluctuating pressures is accounted for in covariance integration.

Characteristics of large pressures in regions of flow separation

Large fluctuating suction pressures are generated in flow separation regions close to the leading edges on the roof of low rise buildings. The flow mechanisms that generate these pressures are the 2D separation bubble for flow perpendicular to the edge discontinuity and the 3D conical vortex for flow at oblique angles to the edge discontinuity. These pressure fluctuations depart from the Gaussian distribution with significantly greater probabilities at the negative tail of the probability distribution. The largest suction pressures are generated close to the leading corner for a wind orientation of ∼ 30°. Conditionally sampled data indicated that progressively larger section pressures in the separation regions were progressively spatially better correlated. Also, time averaged pressures and peak suction pressures were spatially better correlated under the 3D conical vortex than under the 2D separation bubble.

Development of methods for assessing the vulnerability of Australian residential building stock to severe wind

Knowledge of the degree of damage to residential structures expected from severe wind is used to study the benefits from adaptation strategies developed in response to expected changes in wind severity due to climate change. This study will inform government, the insurance industry and provide emergency services with estimates of expected damage. A series of heuristic wind vulnerability curves for Australian residential structures has been developed. In order to provide rigor to the heuristic curves and to enable quantitative assessment to be made of adaptation strategies, work has commenced to produce a simulation tool to quantitatively assess damage to buildings from severe wind. The simulation tool accounts for variability in wind profile, shielding, structural strength, pressure coefficients, building orientation, component self weights, debris damage and water ingress via a Monte Carlo approach. The software takes a component-based approach to modelling building vulnerability. It is based on the premise that overall building damage is strongly related to the failure of key components (i.e. connections). If these failures can be ascertained, and associated damage from debris and water penetration reliably estimated, scenarios of complete building damage can be assessed. This approach has been developed with varying degrees of rigor by researchers around the world and is best practice for the insurance industry.

Wind loads on planar canopy roofs, Part 1: mean pressure distributions

Mean pressure distributions on planar canopy roofs are presented based on 1 : 100 scale wind tunnel measurements obtained in a simulated suburban atmospheric boundary layer. For a range of roof pitch angles and wind directions, point and area-averaged pressure measurements were obtained with the worst loads experienced adjacent to lines of flow separation. In this study, generally smaller wake or suction mean pressures were obtained when compared with the earlier studies of Gumley. These differences are attributed to the interference at separation by the canopy supports in Gumleys work, and the higher level of turbulence in the present study.

Wind load effects and equivalent pressures on low-rise house roofs

Wind loads on the roof of a typical low-rise house are determined by carrying out a wind tunnel model study. The region near the windward gable end are subjected to the largest wind loads. The large suction pressures near the ridge for oblique approach winds exceed data given in AS1170.2. The mean and fluctuating wind pressures and load effects on the roof tributary supported by the second truss from the windward gable end (i.e. truss subjected to the largest wind loads) are analysed in detail. Smaller load effects are generally obtained by applying the covariance integration method with wind tunnel data, compared with values derived from using AS1170.2 data. The equivalent static pressure distributions obtained from the load–response-correlation method are generally smaller than the peak pressures derived from AS1170.2, except near the ridge for oblique approach winds.

The response of the dines anemometer to gusts and comparisonswith cup anemometers

The Dines pressure tube anemometer was the primary wind speed recording instrument used in Australia until it was replaced by Synchrotac cup anemometers in the 1990s. Simultaneous observations of the gust wind speeds recorded using both types of anemometers during tropical cyclones have, however, raised questions about the equivalency of the gust wind speeds recorded using the two instruments. An experimental study of the response of both versions of the Dines anemometer used in Australia shows that the response of the anemometer is dominated by the motion of the float manometer used to record the wind speed. The amplitude response function shows the presence of two resonant peaks, with the amplitude and frequency of the peaks depending on the instrument version and the mean wind speed. Comparison of the gust wind speeds recorded using Dines and Synchrotac anemometers using random process and linear system theory shows that, on average, the low-speed Dines anemometer records values 2%–5% higher than those recorded using a Synchrotac anemometer under the same conditions, while the high-speed Dines anemometer records values 3%–7% higher, depending on the mean wind speed and turbulence intensity. These differences are exacerbated with the adoption of the WMO-recommended 3-s moving average gust wind speed when reporting the Synchrotac anemometer gust wind speeds, rising to 6%–12% and 11%–19% for low- and high-speed Dines anemometers, respectively. These results are consistent with both field observations and an independent extreme value analysis of simultaneously observed gust wind speeds at seven sites in northern Australia.

Peak wind loads under delta wing vortices on canopy roofs

Pressure contour plots on pitched canopy roofs indicate that the largest pressures are experienced close to the leading edges and the ridge line at a wind orientation of ∼ 30°. Surface flow patterns and pressure contour plots identify the flow mechanisms causing these large pressures as flow separation and the formation of conical delta wing vortices. The correlation between fluctuating surface pressures is increased under the delta wing vortex. An eigenvalue analysis shows that the mechanisms contributing most to the large fluctuating pressures close to the leading edges are flow separation and delta wing vortex formation. Area averaged pressures close to the leading edges and the ridge line are substantially greater than the pressures on the rest of the roof.