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CONTENTS
Volume 16, Number 1, January 2013
 

Abstract
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Key Words
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Address
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Abstract
The wind-induced transient response of internal pressure following the creation of a sudden dominant opening during the occurrence of high external pressure, in low-rise residential and industrial buildings was numerically investigated. The values of the ill-defined parameters namely the flow contraction coefficient, loss coefficient and the effective slug length were calibrated by matching the analytical response with the computational fluid dynamics predictions. The effect of a sudden i.e., \'instantaneously created\' windward opening in the Texas Technical University (TTU) test building envelope was studied for two different envelope flexibility-leakage combinations namely: (1) a quasi-statically flexible and non-porous envelope and (2) a quasi-statically flexible and porous envelope. The responses forced by creating the openings at different time leads/lags with respect to the occurrence of the peak external pressure showed that for cases where the openings are created in close temporal proximity to the peak pressure, the transient overshoot values of internal pressure could be higher than the peak values of internal pressure in the pre-sequent or subsequent resonant response. In addition, the influence of time taken for opening creation on the level of overshoot was also investigated for the TTU building for the two different envelope characteristics. Non-dimensional overshoot factors are presented for a variety of cavity volume-opening area combinations for (1) buildings with rigid/quasi-statically flexible non-porous envelope, and (2) buildings with rigid/quasi-statically flexible and porous envelope (representing most low rise residential and industrial buildings). While the factors appear slightly on the high side due to conservative assumptions made in the analysis, a careful consideration regarding the implication of the timing and magnitude of such overshoots during strong gusts, in relation to the steady state internal pressure response in cyclonic regions, is warranted.

Key Words
internal pressure; transient response; low-rise building; envelope flexibility-leakage; nondimensional overshoot factor

Address
T. K. Guha, R.N. Sharma and P.J. Richards : Department of Mechanical Engineering, The University of Auckland, Private Bag 92019, Auckland, New Zealand

Abstract
This paper presents a boundary-layer wind tunnel (BLWT) study on the effect of variable dominant openings on steady and transient responses of wind-induced internal pressure in a low-rise building. The paper presents a parametric study focusing on differences and similarities between transient and steady-state responses, the effects of size and locations of dominant openings and vent openings, and the effects of wind angle of attack. In addition, the necessity of internal volume correction during sudden breaching, i.e., a transient response experiment was investigated. A comparison of the BLWT data with ASCE 7-2010, as well as with limited large-scale data obtained at a \'Wall of Wind\' facility, is presented.

Key Words
internal pressure; dominant openings; sudden breach; compartment; vents; gable roof; volume correction; boundary-layer wind tunnel; wall-of-wind

Address
Amanuel S. Tecle and Girma T. Bitsuamlak : 1Laboratory for Wind Engineering Research, International Hurricane Research Center/Department of Civil and Environmental Engineering, Florida International University, Miami, Florida 33174, USA
Aly Mousaad ALY : WindEEE Research Institute, Western University, London, ON, Canada

Abstract
A dominant opening in a windward wall, which generates large internal pressures in a building, is a critical structural design criterion. The internal pressure fluctuations are a function of the dominant opening area size, internal volume size and external pressure at the opening. In addition, many buildings have background leakage, which can attenuate internal pressure fluctuations. This study examines internal pressure in buildings for a range of dominant opening areas, internal volume sizes and background porosities. The effects of background porosity are incorporated into the governing equation. The ratio of the background leakage area AL to dominant opening area AW is presented in a non-dimensional format through a parameter, 06 = AL/AW. Background porosity was found to attenuate the internal pressure fluctuations when 06 is larger than 0.2. The dominant opening discharge coefficient, k was estimated to lie between 0.05 to 0.40 and the effective background porosity discharge coefficient KL, was estimated to be between 0.05 to 0.50.

Key Words
background porosity; internal pressure; discharge coefficient; Helmholtz resonance; dominant opening; building

Address
P.Y. Kim and J.D. Ginger : School of Engineering and Physical Sciences, James Cook University, Townsville, Queensland, Australia

Abstract
An analytical model of internal pressure response of a leaky and quasi-statically flexible building with a dominant opening is provided by including the effect of the envelope external pressure fluctuations on the roof, in addition to the fluctuating external pressure at the dominant opening. Wind tunnel experiments involving a flexible roof and different building porosities were carried out to validate the analytical predictions. While the effect of envelope flexibility is shown to lower the Helmholtz frequency of the building volume-opening combination, the lowering of the resonant peak in the internal and net roof pressure coefficient spectra is attributed to the increased damping in the system due to inherent background leakage and envelope flexibility. The extent of the damping effects of \'skin\' flexibility and background leakage in moderating the internal and net pressure response under high wind conditions is quantified using the linearized admittance functions developed. Analytical examples provided for different combinations of background leakage and envelope flexibility show that alleviation of internal and net pressure fluctuations due to these factors by as much as 40 and 15% respectively is possible compared to that for a nominally sealed rigid building of the same internal volume and opening size.

Key Words
internal pressure; leaky; quasi-statically flexible; building; dominant opening; wind tunnel experiments; helmholtz frequency; net roof pressure; admittance function

Address
T.K. Guha , R.N. Sharma and P.J. Richards : Department of Mechanical Engineering, The University of Auckland, Private Bag 92019, Auckland, New Zealand

Abstract
This paper describes a study of the influence of a dynamically flexible building structure on pressures inside and net pressures on the roof of low-rise buildings with a dominant opening. It is shown that dynamic interaction between the flexible roof and the internal pressure results in a coupled system that is similar to a two-degree-of-freedom mechanical system consisting of two mass-spring-damper systems with excitation forces acting on both the masses. Two resonant modes are present, the natural frequencies of which can readily be obtained from the model. As observed with quasi-static building flexibility, the effect of increased dynamic flexibility is to reduce the first natural frequency as well as the corresponding peak value of the admittance, the latter being the result of increased damping effects. Consequently, it is found that the internal and net roof pressure fluctuations (RMS coefficients) are also reduced with dynamic flexibility. This model has been validated from experiments conducted using a cylindrical model with a leeward end flexible diaphragm, whereby good match between predicted and measured natural frequencies, and trends in peak admittances and RMS responses with flexibility, were obtained. Furthermore, since significant differences exist between internal and net roof pressure responses obtained from the dynamic flexibility model and those obtained from the quasi-static flexibility model, it is concluded that the quasi-static flexibility assumption may not be applicable to dynamically flexible buildings. Additionally, since sensitivity analyses reveal that the responses are sensitive to both the opening loss coefficient and the roof damping ratio, careful estimates should therefore be made to these parameters first, if predictions from such models are to have significance to real buildings.

Key Words
internal pressure; dominant opening; dynamic flexibility; flexible roof; net roof pressure; helmholtz resonance

Address
Rajnish N Sharma : Department of Mechanical Engineering, The University of Auckland, Private Bag 92019, Auckland, New Zealand

Abstract
A field study of wind-induced internal pressures in a flexible and porous industrial warehouse with a single dominant opening, of various sizes for a range of moderate wind speeds and directions, is reported in this paper. Comparatively weak resonance of internal pressure for oblique windward opening situations, and hardly discernible at other wind directions, is attributed to the inherent leakage and flexibility in the envelope of the building in addition to the moderate wind speeds encountered during the tests. The measured internal pressures agree well with the theoretical predictions obtained by numerically simulating the analytical model of internal pressure for a porous and flexible building with a dominant opening. Ratios of the RMS and peak internal to opening external pressures obtained in the study are presented in a non-dimensional format along with other published full scale measurements and compared with the non-dimensional design equation proposed in recent literature.

Key Words
internal pressure; warehouse; field study; Helmholtz resonance; leakage; flexibility; porous and flexible building; non-dimensional design equation

Address
T.K. Guha, R.N. Sharma and P.J. Richards : Department of Mechanical Engineering, The University of Auckland, Private Bag 92019, Auckland, New Zealand


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