The UWO contribution to the NIST aerodynamic database for wind loads on low buildings: Part 1. Archiving format and basic aerodynamic data

Wind tunnel testing of generic low building models has been carried out at the University of Western Ontario (UWO) in support of an initiative by Texas Tech University (TTU) and the United States National Institute of Standards and Technology (NIST) to create an aerodynamic database for low building design. This paper describes the background of the project, the basic models, testing configurations, the wind simulation, the standard archival format for distribution of the data, and a basic analysis of the data. Part 2 presents a detailed comparison of the data with existing wind load provisions in building codes.Basic quality checks of the data are made via limited comparisons among the data obtained during this study. Parametric comparisons based on roof slope, building height and building plan dimension show that the data obtained within this study are consistent with the expected aerodynamic behaviour. Comparisons with full scale TTU data show that the wind tunnel tests match the full-scale reasonably well, but cannot reproduce the largest of the peak point suctions near roof edges.     

The UWO contribution to the NIST aerodynamic database for wind loads on low buildings: Part 3. Internal pressures

Wind tunnel tests of generic low buildings have been conducted at the University of Western Ontario for contribution to the National Institute on Standards and Technology (NIST) aerodynamic database. Part 1 provided the archiving format and basic aerodynamic data. In Part 2, the data of external pressures were compared with existing wind load provisions for low buildings. This paper, Part 3, deals with an investigation of wind-induced internal pressures of low-rise buildings with realistic dominant opening and leakage scenarios. Data from one building model with four different opening sizes were compared with numerical simulations. The existing theory, using the unsteady orifice discharge equation, works well for the building models used in this study, given the external pressures near the openings, irrespective of shifts of wind direction and upstream terrain. Numerical simulations can capture the temporal variations of the internal pressure fluctuations, as well as mean values.The internal pressure fluctuations for the building with leakage (nominally sealed building) are attenuated as they pass through the openings, while mean values are consistent with spatially averaged external pressures. Internal pressure resonance occurs for the dominant opening (3.3% open ratio) with building leakage. Effects of oblique wind angles on internal pressure dynamics are not significant, at least for the openings in the centre of wall, as is the case herein. Peak internal pressures occur for a wind direction normal to the wall with a dominant opening. Measured internal pressure coefficients are compared with current wind load provisions. Some peak values were found to exceed the recommended design values for the dominant windward wall opening cases.     

Wind effects of parapets on low buildings: Part 2. Structural loads

The present paper, Part 2 in a four part series, focuses on the effects of solid, perimetric parapets on the wind-induced structural loads on low-rise buildings. Roof and wall pressures were measured at more than 500 locations simultaneously for five parapet heights (h=0, 0.46, 0.9, 1.8 and 2.7 m in equivalent full-scale dimensions) and three building heights (H=4.6, 9.1 and 18.3 m) with plan dimensions 31.1 by 61.6 m and a on 12 gable roof slope. The data were obtained in simulated open country and suburban terrain conditions, at a scale of 1:100, in a boundary layer wind tunnel. It was observed that the distance from the eaves edge to the reattachment point for winds normal to the wall increases from x/H∼0.4 for h/(H+h)=0 to x/H=1.8 for h/(H+h)=0.23. While mean and fluctuating point pressure distributions tend to decrease in magnitude with h, the increased areas of separated flow lead to increased loads for interior frames with the taller parapets.     

Wind effects of parapets on low buildings: Part 3. Parapet loads

As part of the study on the effects of parapets on wind-induced loads on low buildings, measurements of the pressures on parapet surfaces have been carried out. Pressures were measured on both the exterior and interior for several parapet heights, h=0.46, 0.9, 1.8, 2.7 m, and building heights, H=4.6, 9.1, 18 m, for both a uniform perimetric parapet and an isolated parapet on one wall. These data were used to quantify the local (component and cladding) and structural wind loads on the parapets. It was found that the worst structural load coefficients over all wind angles are approximately constant with h and H because of opposing trends of the pressures on the interior and exterior parapet surfaces. That is, the loads increase on the interior surface with H (as they do for roof loads), while decreasing on the exterior surface. The current structural load coefficients prescribed by the ASCE 7-02 capture this well for the building configurations considered. However, the suction component and cladding loads on the interior surface of isolated parapets are not well captured by the code.     

Wind effects of parapets on low buildings: Part 4. Mitigation of corner loads with alternative geometries

This is the fourth paper in a series on the wind effects of parapets on low-rise buildings. This part focuses on alternative parapet geometries which can mitigate local (component and cladding) loading due to the formation of corner vortices. It was found that spoilers and porous perimetric parapets significantly reduce the loads for all areas in the corner, edge and interior zones considered. For solid parapets, raising the corner, or putting a slot in the corner are also beneficial when compared to uniform, continuous parapets. Removing the corner of a continuous parapet also lowers the loads as compared to isolated (single) parapets which end at the side wall, indicating that shortened isolated parapets could also be beneficial.     

Wind effects of parapets on low buildings: Part 1. Basic aerodynamics and local loads

This is the first paper in a series on the effects of parapets on the wind-induced loads on low buildings. Part 1 focuses on the basic aerodynamic effects of parapets and the local (components and cladding) loads. Wind tunnel data were obtained from about 700 pressure taps in the area of a corner panel of 3.7 m×7.6 m (equivalent full-scale dimensions) for several parapet heights and configurations. Significant downward loads were observed which exceed code values for all parapet heights. This may be significant when combined with other loads (such as snow or water). It was also found that parapets alter the suction loads on the roof by changing the location of the corner vortex relative to the roof, for continuous perimetric parapets, and the type of vortex formed, for isolated (single wall) parapets. In the ASCE-defined interior region, the measured coefficients for component and cladding loads exceed those in the code for all parapets and areas examined. For the edge zone, the experimental coefficients for areas less than 1 m² exceed the code values (except for tall perimetric parapets). However, it was found that the component and cladding loads in the ASCE 7 adequately envelope the uplift caused by perimetric parapets in the corner zone for H=4.6 m, but not for isolated parapets, in particular for areas less than 1 m². It was also discussed that the ASCE 7 will be unconservative for larger eaves heights since H² is the correct normalizing factor for roof areas beneath the separated flow. Furthermore, the use of edge zone coefficients in the corner zone for h ?0.9 m should be changed to h/(H+h)?0.23 in the ASCE 7.     

Interpolation of pressure time series in an aerodynamic database for low buildings

Database-assisted design (DAD) is a relatively new concept whereby archived pressure time series from wind tunnel experiments are used directly in structural analysis software for the design of a structure. The US National Institute of Standards and Technology (NIST) is currently creating an aerodynamic database of wind-induced pressure time series on the envelope of various low buildings. In order for DAD to be of practical use, simple interpolation schemes must be used to cover the wide range of low building geometries a designer may desire since only relatively few geometries could be included in any database. The approach investigated herein consists of using a set of re-scaled pressure time series from an aerodynamically similar building at the same wind angle and in the same terrain. The set of reference time series are corrected by adjusting their mean and rms. pressure coefficients with artificial neural network models which have captured the variability of these statistical parameters. The use of the re-scaled time series is a simple way to get the correct spatial correlations for the interpolated building without resorting to more elaborate simulation schemes. However, interpolation must be limited to situations where the spatial correlations are similar. The methodology was applied to two test cases with reasonable success.     

Prediction of pressure coefficients on roofs of low buildings using artificial neural networks

This paper describes an artificial neural network (ANN) approach for the prediction of mean and root-mean-square (rms) pressure coefficients on the gable roofs of low buildings. The ANN models, which employ a backpropagation training algorithm, are capable of generalizing the complex, nonlinear functional relationships between the pressure coefficients and eave height, wind direction and spatial location on the roof. The performance of the ANN is demonstrated by the prediction of the pressure coefficients for roof tap locations in a corner bay. The mean bay uplift can be predicted accurately with an average error less than 2% for three cornering wind directions not seen by the ANN during training. The mean-square errors of all of the individual pressure taps in the corner bay were 12% and 9% for the mean and rms coefficients, respectively. This approach could be used to expand aerodynamic databases to a larger variety of geometries and increase its practical feasibility.     

Wind loads on low-rise buildings: a review of the state of the art

This paper refers to the most recent research on wind loads on low-rise buildings. Novel measurement techniques and methodologies are reviewed, and selected experimental results from various studies are presented. Particular emphasis is given to works aimed at the formulation of codified data, i.e. results appropriate for incorporation into design standards and codes of practice. Only either full-scale studies or those done under conditions simulating the earth's atmospheric boundary layer have been considered. Comparisons between full-scale and laboratory results are discussed. Areas requiring additional research and analysis are identified.     

Extreme wind load estimates based on the Gumbel distribution of dynamic pressures: an assessment

We present a contribution to the current debate on whether it is more appropriate to fit a Gumbel distribution to the time series of the extreme dynamic pressures (i.e. of the squares of the extreme wind speeds) than to fit an extreme value distribution to the time series of the extreme wind speeds themselves. It has been shown that the use of time series of the extreme dynamic pressures would be justified if the time series of the wind speed data taken at small intervals (e.g. 1 h) were, at least approximately, Rayleigh-distributed. We show that, according to sets of data we believe are typical, this is not the case. In addition, we show results of probability plot correlation coefficient (PPCC) analyses of 100 records of sample size 23 to 54, according to which the fit of reverse Weibull distributions to largest yearly wind speeds is considerably better than the fit of Gumbel distributions to the corresponding largest yearly dynamic pressures. We interpret the data and results presented in the paper as indicating that there is no convincing support to date for the hypothesis that the Gumbel distribution should be used as a model of extreme dynamic pressures.     

Wind tunnel tests on the relationship between building density and pedestrian-level wind velocity: Development of guidelines for realizing acceptable wind environment in residential neighborhoods

The main purpose of this study is to reveal the relationship between the building density and the average wind velocity at pedestrian level in residential neighborhoods. This paper firstly presents the results of wind tunnel tests on 22 residential neighborhoods selected from actual Japanese cities. The results show that there is a strong relationship between the gross building coverage ratio and the mean wind velocity ratio. Secondly, the wind environment evaluation for case study areas is performed by using the wind tunnel results and the climatic conditions of several major Japanese cities. The development method of guidelines for realizing acceptable wind environment in residential neighborhoods using the gross building coverage ratio is proposed.     

Guidelines for the required time resolution of meteorological input data for wind-driven rain calculations on buildings

An important question in wind-driven rain (WDR) calculations on buildings, either with semi-empirical formulae or with Computational Fluid Dynamics (CFD), concerns the required time resolution of the meteorological input data: wind speed, wind direction and horizontal rainfall intensity. Earlier work has indicated that the use of 10 min input data can provide accurate results, while the use of arithmetically averaged hourly data can yield significant underestimations in the calculated WDR amounts. This paper builds further on this earlier work by providing a detailed investigation of the parameters that determine the required time resolution for WDR calculations on building facades: (1) the averaging technique, (2) the building geometry and the position at the building facade and (3) the type of the rain event. It is shown that all three parameters can have a large influence on the required time resolution. Depending on these parameters, hourly or even daily wind and rain input data could provide accurate results, while in other situations they can lead to very large errors. Finally, guidelines for the required time resolution as a function of the influencing parameters are provided.     

Evaluation of the corrected seasonal energy demand, for buildings classification, to be compared with a standard performance scale

In the European panorama, the relevant increase of the buildings energy consumptions has resulted, from the normative point of view (European directive 2002/91/EC [European Parliament and Council of December 16th, 2002 on the energy performance of buildings, Official Journal of the European Communities, L 1/65] and the relative national norms - for example Italian Decrees 192/05-311/06), in the imposition of minimum standards of construction, limiting the specific energy requirements specifically for heating and cooling. Moreover, in some countries it is being started to introduce, for buildings that respect the minimum performances levels imposed, incentive and defiscalization measures, function of their particular energetic efficiency and the corresponding performance class.Therefore, to compare the construction quality of different buildings, through energy performance classification, the authors propose a procedure for the determination of the corrected energy demand, separately for heating and cooling, independent of buildings location and directly comparable to a standard seasonal performance scale, defined on the entire territory of application.The procedure is so developed through simulation on a wide range of case-studies and then tested on a different buildings set: its effectiveness results in the attribution to each building test of an univocal performance class, providing an energy performance evaluation not affected by the building localization.     

On the estimation of wind speed in urban canyons for ventilation purposes—Part 2: Using of data driven techniques to calculate the more probable wind speed in urban canyons for low ambient wind speeds

For low ambient wind speeds, airflow in deep urban canyons is characterized by a high scatter and important fluctuation as no coupling is established between the undisturbed wind flow and the flow inside the canyon. Thus, thermal and mechanical forces determine the wind speed characteristics. Existing studies based on experimental comparison have shown that under the above boundary conditions, deterministic models may predict with sufficient accuracy the mean wind speed but not the fluctuation caused by the thermal phenomena.     

'EUROPART'. Airborne particles in the indoor environment. A European interdisciplinary review of scientific evidence on associations between exposure to particles in buildings and health effects

The relevance of particle mass, surface area or number concentration as risk indicators for health effects in non-industrial buildings has been assessed by a European interdisciplinary group of researchers (called EUROPART) by reviewing papers identified in Medline, Toxline, and OSH. Studies dealing with dermal effects or cancer or specifically addressing environmental tobacco smoke, house dust-mite, cockroach or animal allergens, microorganisms and pesticides were excluded. A total of 70 papers were reviewed, and eight were identified for the final review: Five experimental studies involving mainly healthy subjects, two cross-sectional office studies and one longitudinal study among elderly on cardiovascular effects. From most studies, no definite conclusions could be drawn. Overall, the group concluded that there is inadequate scientific evidence that airborne, indoor particulate mass or number concentrations can be used as generally applicable risk indicators of health effects in non-industrial buildings and consequently that there is inadequate scientific evidence for establishing limit values or guidelines for particulate mass or number concentrations.     

A Study of Human Reactions to Emissions from Building Materials in Climate Chambers. Part II: VOC Measurements,Mouse Bioassay,and Decipol Evaluation in the 1–2 mg/m3 TVOC Range

Monitoring of human reactions to the emission of formaldehyde and volatile organic compounds (VOC) from four commonly used building materials was carried out. The building materials were: a painted gypsum board, a rubber floor, a nylon carpet, and a particle board with an acid-curing paint. The exposures were performed in climate chambers. The air quality was quantified on the decipol scale by a trained panel, measurements of formaldehyde and VOC being performed simultaneously. The irritating potency of the materials was measured by a mouse bioassay. The VOC measurements showed several malodorants and irritants. Some abundant VOC identified in the head-space analyses were absent in the climate chamber air. The rubber floor and the nylon carpet exhibited a marked increase in decipols compatible with a number of odorous VOC identified in the air. A high formaldehyde concentration (minimum 743μg/m³) was measured for the particle board coated with an acid-curing paint. This was not reflected by a corresponding relatively high decipol value but a long-lasting irritating potency was observed in the mouse bioassay. TVOC sampled on Tenax and expressed in mass per volume as well as in molar concentration, and decipol evaluation both have limitations and should be used with caution as indicators of (perceived) indoor air quality. Eye irritation expressed by means of the eye index reflecting the tear film quality index (comprised of break-up time, foam formation, thickness of the precorneal lipid layer of the tear film, and epithelial damage) was found to be insensitive to formaldehyde and a VOC mixture but sensitive to TVOC concentrations of 1–2 mg/m³. Lipophilic VOC may be the cause of reduced tear film quality by destabilization of the lipid multilayer of the tear film.