Wind Loading Standards Research Articles

Numerical Investigation of Wind Flow and Speedup Effect at a Towering Peak Extending out of a Steep Mountainside: Implications for Landscape Platforms

Wind flow over complex terrain is strongly influenced by the topographical features of the region, resulting in unpredictable local wind characteristics. This paper employs numerical simulation to study the wind flow at a towering peak extending out of a steep mountainside and the wind-induced effect on onsite landscape platforms. First, the wind flow from seven different directions is explored via 3D numerical simulations, and the wind load distribution on the platforms is highlighted. Second, a 2D numerical simulation is conducted to evaluate the wind speedup effect at the side peak, examining the influence of the side peak height and the mountainside steepness on the wind speedup factor. The numerical simulations presented in this research were validated by replicating a published numerical and experimental study. The results illustrate the amplifying and blocking effects of the surrounding topography, yielding unpredictable and nonuniform wind pressure distribution on the platforms. The presence of the side peak leads to a significant increase in the speedup factor, and the side peak height and the mountainside steepness have a moderate influence on the value of the speedup factor. Additionally, the speedup factor obtained from this study varies significantly, especially near the surface, from the recommendations of several wind load standards. Consequently, the impact of the local terrain and the wind speedup effect must be thoroughly assessed to ensure the structural integrity of structures installed at a similar topography.

Exploring the impact of vertically separated flows on wind loads of multi-level structures

The complex dynamics of vertically separated flows pose a significant challenge when it comes to assessing the wind loads on multi-level structures, demanding a nuanced understanding of the intricate interplay between atmospheric conditions and architectural designs. Previous studies and wind loading standards provide insufficient guidance for designing wind pressures on multi-level buildings. The behavior of wind around perpendicularly attached surfaces is not quite similar to that of individual flat roofs or walls. When a body is composed of several surfaces with right or oblique angles, the separated flow from surfaces and their interactions will cause complex flow patterns around each surface. A wind tunnel experimental study was carried out on bluff bodies with attached flat plates and other adjacent bluff bodies with different heights to examine the wind-induced pressures on such complex shapes. Mean and peak pressure coefficients were measured to determine the flow interaction patterns and location of localized peak pressures. The results were compared to the Tokyo Polytechnic University Aerodynamic Database of isolated low-rise buildings without eaves. The research findings indicated that there was a noteworthy disparity between the minimum and maximum values and locations of peak pressures on both the wall and roof surfaces of the models used in this study, as compared to the results obtained by the Tokyo Polytechnic University. Moreover, the study conceivably pointed to the difference between the peak negative and positive pressure coefficient locations with the ASCE 7-22 wind loading zones. The peak suction zones were affected by the combined flows at perpendicular faces, and as a result, different wind load zones were obtained dissimilar to those introduced by ASCE 7-22. Wind loading standards may need to be modified to account for the wind pressures on complex building structures with an emphasis on the location of the peak negative pressure zones.

EFFECTS OF ROOF SHAPES ON WIND PRESSURE DISTRIBUTION OF MULTI-SPAN LOW-RISE BUILDINGS

The present study demonstrates the numerical investigation to find out the effects of roof shapes on the wind pressure distribution of multi-span low-rise buildings. Most of the wind load standards of various nations are provided with wind load information of isolated low-rise buildings which in turn practically came out to be inapplicable during the designing of low-rise buildings with multi-spans. Also, most of the wind load studies are carried out using boundary layer wind tunnel (BWLT) which is sometimes not available, time taking process, and is expensive. Therefore, in the present research, numerical simulation has been done for the model of a low-rise building. For investigation, the Ansys CFX platform has been used with the k-ε turbulence model for different angles of wind incidence at an interval of 15°. The wind pressure distribution has been investigated for the model low-rise building with a rectangular plan having six spans of different roof forms i.e., cylindrical roof, mono-slope roof, hip roof, and dome roof. The outcomes of the present numerical investigations are presented in the contour plots of wind pressure and coefficients of wind-induced pressure on the different roof forms of low-rise buildings. The outcomes of the study will be so much beneficial to structural design engineers while considering the wind loads calculations on the different roof forms for low-rise buildings.

Determination of wind loads on porous sunshade roof cover sheets using conversion factor

Porous sunshade roof cover sheets installed on building roofs are new structures for mitigating heat absorption. Thus, there have been few studies on wind flow and its effects on wind-permeable structures, and there is no provision for these structures in the major international wind load standards and codes. Unlike wind loading on building roofs, wind loading on porous sunshade roof cover sheets is a combination of wind pressures on both the upper and lower surfaces, which complicates the calculation of wind loading. From the viewpoint of structural design, we need a simple method for determining wind loading on these structures. Wind tunnel tests have been carried out for various wind angles, three porosities (ratio between area of orifices and area of sheet), and five gaps between sheet and roof, and results have been analyzed. As a result, the author proposes a simple formula for calculating wind loading on porous sunshade roof cover sheets from wind loadings on normal building roofs available from wind loading codes and standards. The calculated results based on this formula and the Japanese wind loading standard (AIJ-RFLB (2015))[4] are compared with those of wind tunnel tests. There is a good similarity between them.

Minimising damage to houses by designing for high internal pressures

Internal pressurisation of buildings during a severe wind event, such as a tropical cyclone or thunderstorm, can often cause severe structural failures, as observed during damage investigations. Wind loading standards worldwide provide design data for internal pressure design. However, the implementation of these data often depends on the location of the building in relation to the levels of wind hazard in the relevant country. Recent observations during Tropical Cyclone (TC) Seroja in an intermediate wind region (wind region B) in Western Australia indicated the need for the design for full internal pressures of buildings in this wind region. This paper presents an overview of the damage investigation conducted after TC Seroja that highlights significant damage to buildings due to the lack of design for internal pressures. Additionally, a case study of a house modelled using the vulnerability analysis software VAWS is presented showing the improvements in the performance of buildings designed for internal pressures. TheVAWS models showed that both the design for full internal pressure and the use of debris rated shutters were both effective at reducing the level of serious structural damage and making houses more resilient. The robustness and resilience of buildings increase significantly if they are designed for high internal pressure because the failure of a window or door (a local failure) will not lead to a major structural failure.

Using large climate model ensembles to assess historical and future tropical cyclone activity along the Australian east coast

Assessing regional changes in tropical cyclones (TCs) and their future impacts are challenging given the short historical record and limited sample size of these extreme events. To address this, we use large climate model ensembles to increase sample size and explore historical variability and future changes in regional TC behavior. We demonstrate this approach on basin and sub-basin scales along Australia's East Coast. Applying a TC tracking algorithm to the large ensembles, we find that the large ensembles are skillful in detecting observed historical TC trends in the Southwest Pacific (SWP) basin. Furthermore, we show that projected TC activity in the SWP basin exposes larger land areas to extreme winds and high precipitation totals. This includes southern-most portions of the SWP basin, where future TC wind speeds regularly exceed current wind loading standards. Combined, our results point to rapidly increasing risks of damaging TC winds and major TC flooding, as well as a heightened risk of water ingress through wind-driven rain.

Using historical tropical cyclone climate datasets to examine wind speed recurrence for coastal Australia

Likelihood estimates of extreme winds, including those from tropical cyclones (TCs) at certain locations are used to inform wind load standards for structural design. Here, wind speed average recurrence intervals (ARIs) determined from TC climate data dating back to the 1970s in two quantile–quantile adjusted reanalysis datasets (ERA5 and BARRA [1990]), and best-track observations for context, were compared with Standardized ARIs (AS/NZS) across seven tropical and two subtropical Australian inland coastal regions. The novelty of this work lies in determining TC-wind speed ARIs from a range of datasets that are not typically used to evaluate this metric. Inherent differences between the data used to determine the Standard ARIs (large sample size allow for larger extrapolations; GEV function) and TC data ARIs (smaller sample size and less certain data; the more asymptotic Lognormal/Weibull functions are used) led to the use of different extreme value functions. Results indicated that although these are two distinct ways of determining design wind speeds, when they are considered equivalent, there was a moderate reproduction of the ARI curves with respect to the Standard in both reanalysis datasets, suggesting that similar analyses using climate model products can provide useful information on these types of metrics with some caveats. Trends in TC wind strength affecting coastal Australia were also analyzed, indicating a potential slight downtrend in tropical West coast TC wind strength and slight uptrend for tropical East coast TC wind strength, noting considerable uncertainty given the short time period and limitations of data quality including over longer time periods. Such trends are not only limited to the relationship between TC intensity and anthropogenic warming, but also to regional changes in TC frequency and track direction. This could lead to significant trends emerging in regional Australian TC wind gust strength before several decades of warming have occurred. It is hoped that climate models can provide both longer-term and a more homogenous base for these types of evaluations and subsequent projections with respect to climate change simulations.

On the deviation of mean pressure coefficients in wind loading standards for a low-rise, gable-roofed building with boundary walls

The provisions in wind loading standards routinely overlook the influence of nearby small-size objects on wind loads of low-rise buildings. One such object is boundary walls that significantly modify the surrounding wind field thereby affecting the wind loading of low-rise buildings. To investigate this phenomenon, four low-rise, gable-roofed buildings: one with and three without boundary walls were tested in a boundary layer wind tunnel. The calculated external pressure coefficients (C¯p) were subsequently compared with the provisions given in ASCE 7 (2016), NBCC (2015), EN 1991-1-4 (2005), and AS/NZS 1170.2 (2011). The comparison showed a good agreement for the C¯p calculated using ASCE 7-16 (2016) and AS/NZS 1170.2 (2011) for the building without boundary walls with those of the wind tunnel test. However, all wind loading standards overestimated C¯p of the buildings with boundary walls because they did not account for the shielding effect of boundary walls. The largest discrepancies in magnitude and distribution of wind pressure were observed on the windward wall and the upwind roof slope. These modifications showed a strong dependency on the upstream and lateral separation distances between the building and the boundary walls.

Wind loads on double-skillion roof houses

ABSTRACT 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

A study of aerodynamic pressures on elevated houses

In coastal residential communities, especially along the coastline, flooding is a frequent natural hazard that impacts the area. To reduce the adverse effects of flooding, it is recommended to elevate coastal buildings to a certain safe level. However, post storm damage assessment has revealed severe damages sustained by elevated buildings' components such as roofs, walls, and floors. By elevating a structure and creating air gap underneath the floor, the wind velocity increases and the aerodynamics change. This results in varying wind loading and pressure distribution that are different from their slab on grade counterparts. To fill the current knowledge gap, a large-scale aerodynamic wind testing was conducted at the Wall of Wind experimental facility to evaluate the wind pressure distribution over the surfaces of a low-rise gable roof single-story elevated house. The study considered three different stilt heights. This paper presents the observed changes in local and area averaged peak pressure coefficients for the building surfaces of the studied cases. The aerodynamics of the elevated structures are explained. Comparisons are done with ASCE 7-16 and AS/NZS 1170.2 wind loading standards. For the floor surface, the study suggests a wind pressure zoning and pressure coefficients for each stilt height.

Wind loads on buildings: A code of practice perspective

The paper reviews the wind loading of buildings from a code perspective. The Canadian wind load provisions for buildings, due primarily to the ingenuity of Alan G. Davenport, have gained an international reputation after recognition for their innovative and pioneering character by researchers and practitioners across the globe. In this regard, these provisions have been influential in the development and evolution of various national and international wind load standards, including the ASCE 7, the ISO wind load standard, the Eurocode, the China standard for wind loads on roof structures and others. The paper provides first an overview of ASCE 7 (USA), NBCC (Canada) and GB 50009 (China) to gain some insight into the extent to which the external pressures, internal pressures, exposure issues and topography - among others - are currently being addressed through these provisions. The current similarities and differences among wind load provisions for buildings are outlined and attempts are made to resolve some of the apparent discrepancies leading to possibly non-conservative results. Ultimately, innovative codification approaches and trends currently under discussion, development and consideration are also presented.

CFD validation of wind pressure distribution on a tall building under the influence of upstream terrain

It is essential to investigate the pressure distribution, aerodynamic coefficients and wind flow fields in-order to predict the wind loads and wind behaviour in building environments. Most of the investigations and international wind load standards haven't highlighted the wind load and wind environment on-and-around buildings under different terrains. The main objective of this investigation is to explore a practical numerical approach for the accurate estimation of wind loads and their impact on buildings under different upstream conditions. In this investigation, simulations are done in IDDES turbulence model along with the formulation of k-ω SST using CFD. Results indicated the influence of ground roughness in pressure distribution on building faces. Furthermore, CFD results over-predicted the experimental values near the edges due to strong shear-flow and expanding wake-vortices. The cross-validation of the mean drag coefficients showed good-agreement. Hence this investigation promotes the practice of IDDES in wind-resistant designs for tall buildings.

Mean pressure coefficient distributions over hyperbolic paraboloid roof and canopy structures with different shape parameters in a uniform flow with very small turbulence

The hyperbolic paraboloid with two high and low corners is the most basic anticlastic double curved shape of tensile surface structures. However, this shape is currently not considered in the existing wind load standards and only very few investigations are documented in literature. Therefore, this study aims to map the mean aerodynamics over hyperbolic paraboloid roofs and extremely thin canopies to help engineers understand the general aerodynamics of these structures. In this study, scaled wind tunnel testing is performed on rigid models of a roof with enclosing walls and a canopy without enclosing walls to draft mean Cp-distributions and standard deviations for various wind orientations. These mean Cp-distributions are validated with the limited studies in literature and used to calibrate and benchmark a numerical wind tunnel, using CFD RANS simulations, that allows to further reduce the thickness of the canopy compared to the wind tunnel models. The numerical wind tunnel is used to study the mean wind load distributions for hyperbolic paraboloid roofs and canopies with different surface curvature for the most important wind orientations. The results in this paper show good agreement between wind tunnel experiments and CFD simulations, with similar variations as established by different studies of the Silsoe cube. First mean Cp-distributions obtained with scaled wind tunnel testing are presented for hyperbolic paraboloid canopies of only 5 mm thick, with similar mean net Cp and only slightly larger suction over the upper and lower face compared to the numerical results for a zero-thickness canopy. The numerical study of different surface curvatures indicates different geometrical patterns in the mean Cp-distributions when the flow starts to separate for highly curved hypars. In general, suction and pressure increase for higher surface curvature, with similar geometrical patterns in the mean Cp-distributions, as long as the flow remains attached. If the flow separates for highly curved hypars, the geometrical pattern differs and the mean Cp drops due to the different behavior of the flow. Finally, the presented mean Cp-distributions give insight in the aerodynamics of hypar roofs and canopies with different surface curvature and could form a basis for future analysis towards peak loads for the design of these structures.

Wind speed measurements and predictions over Belmont Hill, Wellington, New Zealand

The aim of the research described in this paper is to reduce the vulnerability of New Zealand's built infrastructure to wind damage through provision of improved wind speed prediction procedures for wind flow over complex terrain that could ultimately be incorporated into the AS/NZS 1170.2 loading standard. This paper presents results from a specific experiment which compares measured wind speedups (neutral atmosphere) over the rugged Belmont Hill region with wind speedups estimated from AS/NZS 1170.2 by two organisations, and from six other international wind-loading standards, through Computational Fluid Dynamics (Gerris and WAsP) modelling, and through wind-tunnel modelling. It was found that computer modelling with the large-eddy simulation CFD code Gerris and wind-tunnel measurements, agree remarkably well with the observations and differentiate considerably better between areas exposed or sheltered by the local terrain features compared to applying the CFD code WAsP (4.1), or applying the AS/NZS 1170.2 wind-loading standard. Furthermore, it was found that the AS/NZS1170.2 predictions differed significantly when carried out by different organisations. The wind speedup prediction methods from the six other international standards all use similar approaches and thus the predictions from all of them were quite similar, and did not agree particularly well with the field measurements.

Prototyping of thin shell wind tunnel models to facilitate experimental wind load analysis on curved canopy structures

The topologies of membrane and shell structures are not covered by existing wind load Standards and wind tunnel testing should be used to obtain representative wind loads for these structures. However, accurate scale-models of these organically shaped and often open thin structures are complex, time-consuming and expensive to build. To stimulate experimental research on wind load distributions over these structures, this paper illustrates a prototyping methodology for double curved thin shell wind tunnel models with integrated pressure sensors. The production process is illustrated for a hyperbolic paraboloid roof structure. The obtained wind load distributions are validated with literature for a flat roof and canopy that is made according to the same methodology and for two hyperbolic paraboloid roofs. Results indicate that, compared to conventional wind tunnel models, these thin shell wind tunnel models yield more realistic wind pressure distributions over very thin canopy structures. Finally, Cp-distributions are shown for the hyperbolic paraboloid canopy with the high corner under attack. The production of glass-fibre reinforced composites in a CNC-milled mould is convenient and accurate and facilitates the production of wind tunnel models to be used for wind load measurements on organically shaped thin canopy structures.

Pull-through capacities of cold-formed steel roof battens considering loading rate sensitivity

Static and fatigue pull-through failures of thin steel roof battens in the vicinity of batten to rafter screw connections are part of the major premature connection failures which lead to severe roof failures during high wind events. As wind speed and thereby wind uplift loading rate on a building roof varies over a wide range, the loading rate which should be used to conduct prototype roof tests is a moot point. Current wind loading standards and guidelines recommend a wider range of loading rates/frequencies in simulating static and cyclic wind loads. This could adversely affect the test results of loading/strain rate sensitive materials. Since cold-formed steels appear to be sensitive to loading rate, it is necessary to investigate the effect of loading rate on both static and fatigue pull-through capacities of cold-formed steel roof battens. Therefore, a series of static and cyclic pull-through tests was conducted at various loading rates on roof battens made of two grades (G300 and G550) and two thicknesses (0.75/0.80 and 0.95/1.00 mm). Test results showed that both static and fatigue pull-through capacities increase with increasing loading rate. To understand the loading rate sensitivity of roof battens, the effect of loading rate on the ultimate tensile strength of cold-formed steels was also investigated through a series of tensile coupon tests. Based on both pull-through and tensile coupon test results, suitable modifications and recommendations have been made to the current pull-through capacity equations and the current Low-High-Low (LHL) cyclic test loading frequency. A suitable material model is also proposed to determine the dynamic mechanical properties of cold-formed steels.

Comparison of Speed-Up Over Hills Derived from Wind-Tunnel Experiments, Wind-Loading Standards, and Numerical Modelling

We evaluate the accuracy of the speed-up provided in several wind-loading standards by comparison with wind-tunnel measurements and numerical predictions, which are carried out at a nominal scale of 1:500 and full-scale, respectively. Airflow over two- and three-dimensional bell-shaped hills is numerically modelled using the Reynolds-averaged Navier–Stokes method with a pressure-driven atmospheric boundary layer and three different turbulence models. Investigated in detail are the effects of grid size on the speed-up and flow separation, as well as the resulting uncertainties in the numerical simulations. Good agreement is obtained between the numerical prediction of speed-up, as well as the wake region size and location, with that according to large-eddy simulations and the wind-tunnel results. The numerical results demonstrate the ability to predict the airflow over a hill with good accuracy with considerably less computational time than for large-eddy simulation. Numerical simulations for a three-dimensional hill show that the speed-up and the wake region decrease significantly when compared with the flow over two-dimensional hills due to the secondary flow around three-dimensional hills. Different hill slopes and shapes are simulated numerically to investigate the effect of hill profile on the speed-up. In comparison with more peaked hill crests, flat-topped hills have a lower speed-up at the crest up to heights of about half the hill height, for which none of the standards gives entirely satisfactory values of speed-up. Overall, the latest versions of the National Building Code of Canada and the Australian and New Zealand Standard give the best predictions of wind speed over isolated hills.

Analysis of Wind Pressure Coefficient for Spatial Structure Roofs by Wind Load Standards and Wind Tunnel Tests

Analysis of Wind Pressure Coefficient for Spatial Structure Roofs by Wind Load Standards and Wind Tunnel Tests

Comparison of Static Wind Load on High Rise Building According to Different Wind Loading Codes and Standards

Comparison of Static Wind Load on High Rise Building According to Different Wind Loading Codes and Standards

Wind loads on contemporary Australian housing

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.