JDH Consulting

Mentone, Australia

JDH Consulting

Mentone, Australia
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Holmes J.D.,JDH Consulting
Wind and Structures, An International Journal | Year: 2010

This review paper discusses research from the last few years relating to windborne debris risk models and the essential elements of engineering damage prediction models. Generic types of windborne debris are discussed. The results of studies of debris trajectories that are relevant to damage models are described- in particular the horizontal component of debris velocity as a function of distance travelled. The merits of impact momentum versus impact kinetic energy as a relevant parameter for predicting damage are considered, and how published data from generic cannon impact tests can be used in risk models. The quantitative variation of debris impact damage with wind speed is also discussed. Finally the main elements of previously-proposed debris damage models are described.


Miller C.,University of Western Ontario | Holmes J.,JDH Consulting | Henderson D.,James Cook University | Ginger J.,James Cook University | Morrison M.,University of Western Ontario
Journal of Atmospheric and Oceanic Technology | Year: 2013

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. © 2013 American Meteorological Society.


Harper B.A.,Pty. Ltd. | Holmes J.D.,JDH Consulting | Kepert J.D.,Center for Australian Weather and Climate Research | Mason L.B.,University of Tasmania | Vickery P.J.,Applied Research Associates Inc.
Journal of Applied Meteorology and Climatology | Year: 2012

Cook and Nicholls recently argued in this journal that the city of Darwin (Northern Territory), Australia, should be located in wind regionDrather than in the current region C in theAustralian/New Zealand Standard AS/NZS 1170.2 wind actions standard, in which region D has significantly higher risk. These comments critically examine the methods used by Cook and Nicholls and find serious flaws in them, sufficient to invalidate their conclusions. Specific flaws include 1) invalid assumptions in their analysis method, including that cyclones are assumed to be at the maximum intensity along their entire path across the sampling circle even after they have crossed extensive land areas; 2) a lack of verification that the simulated cyclone tracks are consistent with the known climatological data and in particular that the annual rate of simulated cyclones at each station greatly exceeds the numbers recorded for the entire Australian region; and 3) the apparent omission of key cyclones when comparing the risk at Darwin with two other locations. It is shown here that the number of cyclones that have affected Port Hedland (Western Australia), a site in Australia's region D, greatly exceeds the number that have influenced Darwin over the same period for any chosen threshold of intensity. Analysis of the recorded gusts from anemometers at Port Hedland and Darwin that is presented here further supports this result. On the basis of this evidence, the authors conclude that Darwin's tropical cyclone wind risk is adequately described by its current location in region C. © 2012 American Meteorological Society.


Holmes J.D.,JDH Consulting
Journal of Wind Engineering and Industrial Aerodynamics | Year: 2014

In this paper, predictions of along-wind base moments for a generic tall building from several wind tunnels from an international benchmark study, are compared with those from three codes and standards: the Hong Kong Code of Practice (2004), the Australian/New Zealand Standard, and the American Standard (ASCE 7). There are significant differences in the predictions from the codes, with two of the codes producing lower values than the average of the wind tunnel data. In the case of the Hong Kong Code, the specified drag coefficients for the building are significantly lower than the effective drag coefficients derived from the other standards, and from the measurements. The lower predictions from ASCE 7 can be partly attributed to an apparent inconsistent formulation in the numerator of the expression for the gust effect factor for dynamic structures.Predictions of cross-wind base moments and resultant accelerations from the Australian/New Zealand Standard, have also been compared with the wind-tunnel data. The comparisons are good, with the Standard giving predictions close to the averages of the wind-tunnel data for the cross-wind moments, and close to the upper limits of the wind-tunnel data for the resultant accelerations. © 2014 Elsevier Ltd.


Holmes J.D.,JDH Consulting | Tse T.K.T.,HKUST
Wind and Structures, An International Journal | Year: 2014

A summary ofthe main results from an international comparative study for the high-frequency base balance is given. Two buildings were specified -a 'basic'and an 'advanced' building. The latter had more complex dynamic response with coupled modes of vibration. The predicted base moments generally showed good agreement amongst the participating groups, but less good agreement was found for the roof accelerations which are dominated by the resonant response, and subject to measurement errors for the generalized force spectra, to varying mode shape correction techniques, and different methodsused for combining acceleration components. © 2014 Techno-Press, Ltd.


Ginger J.D.,James Cook University | Holmes J.D.,JDH Consulting | Kim P.Y.,James Cook University
Journal of Structural Engineering | Year: 2010

A dominant opening in a windward wall will generate large positive internal pressures during windstorms, which, in combination with large suction pressures on the roof, commonly causes building failures and is hence a governing design criterion. The fluctuating (and peak) internal pressures are dependent on the external pressure and the size of the opening and the size of the building volume. This study presents ratios of internal pressure to external pressure standard deviations and peaks in terms of the nondimensional opening size to volume parameter, S, and the size of the dominant opening and discharge coefficient. The study also analyzes equations that have been proposed as design formulas for inclusion in codes and standards. © 2010 ASCE.


Holmes J.,JDH Consulting | Allsop A.,Arup
12th Americas Conference on Wind Engineering 2013, ACWE 2013: Wind Effects on Structures, Communities, and Energy Generation | Year: 2013

This paper discusses the appropriate duration for basic gust wind speeds in wind loading codes and standards. Although various proposed definitions are discussed, the 'moving average' gust duration has been accepted internationally, and is suggested as the appropriate one for use by wind engineers. Various historical definitions or descriptions are discussed and compared with the 'moving average' gust duration that has been more recently accepted internationally by the World Meteorological Organization (WMO) for gust speed recording. By this definition, gust durations for analogue outputs from various anemometers are shown to be generally less than 1 second, even though these were historically described as '3-second gust'. It is shown that a 3-second moving digital average, as suggested for gust reporting by the World Meteorological Organization, has significant attenuation effects on wind spectra at design wind speeds, and is equivalent to the filtering of a structure with a frontal area equivalent to that of a typical tall building in a city centre. Hence, for codes and standards that have adopted the WMO 3- second gust as a basis (such as ASCE 7), it is appropriate that 'gust effect factors' greater than 1.0 should be adopted for small structures, or that another adjustment should be made to correct the design pressures.


Holmes J.D.,JDH Consulting | Ginger J.D.,James Cook University
Australian Journal of Structural Engineering | Year: 2012

This paper discusses the rationale behind the redefinition of the design gust speed in the Australian/New Zealand Standard for Wind Actions, AS/NZS 11 70.2, as one with a duration of 0.2 seconds, based on a moving average of that time. The origin of the basic gust in the Australian Standards since 1971, from the Dines anemometer, is discussed, and the relative response of that anemometer to gusts is compared with the current recording system based on cup anemometers, with digital processing including a moving average filter. The cup anemometers in the automatic weather stations (AWS), with the associated 3-second digital averaging, that have replaced the Dines in Australia, since the early 1990s, are shown to significantly attenuate the high frequency wind fluctuations, and hence record lower gust wind speeds. The correction factors provided in the paper for the post-1990 gusts should be applied by writers of future editions of the standard wishing to use AWS data. It should be noted that users of the standard will not be affected by the redefinition as there will be no changes to either the wind speeds or the shape factors. © Institution of Engineers Australia, 2012.


Holmes J.,JDH Consulting
12th Americas Conference on Wind Engineering 2013, ACWE 2013: Wind Effects on Structures, Communities, and Energy Generation | Year: 2013

In this paper, predictions of along-wind base moments for a generic tall building from seven wind tunnels from an international benchmark study, are compared with those from three codes and standards, including ASCE 7. There are significant differences in the predictions, with two of the codes producing significantly lower values than the average of the wind tunnel data. The lower predictions from ASCE 7 can be partly attributed to an apparent inconsistent formulation in the numerator of the expression for the gust effect factor for dynamic structures.


Holmes J.D.,JDH Consulting | Ginger J.D.,James Cook University
Journal of Wind Engineering and Industrial Aerodynamics | Year: 2012

A building with a dominant opening in a wall may experience internal pressures equal to, or greater than, the external wind pressures in a severe windstorm. This is a critical design case in severe wind events, during which accidental openings may be produced by windborne debris or by direct wind loading. This paper reviews previous work on the prediction of fluctuating and peak internal pressures arising from a dominant opening on a windward wall, and summarizes proposed, or current, code formulations in a unified non-dimensional format. Experimental data from a number of sources are plotted together, and are found to fall into two groups, depending on the turbulence intensity in the approach flow. It is shown that the proposed relationships for the ratio of internal to external pressure fluctuations differ considerably, depending on the assumptions made. An intermediate relationship, which agrees well with experimental data in approach flow with turbulence intensities representative of atmospheric wind flow in developed boundary layers, is presented, and a design example of its application is given. © 2011 Elsevier Ltd.

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