Abstract
This report presents the findings of a one-year monitoring effort to empirically characterizernand evaluate the nature of near-ground winds for structural engineering purposes. The current windrnengineering practice in the United States does not explicitly consider certain important near-ground windrncharacteristics in typical rough terrain conditions and the possible effect on efficient design of low-risernstructures, such as homes and other light-frame buildings that comprise most of the building population.rnTherefore, near ground wind data was collected for the purpose of comparing actual near-ground windrncharacteristics to the current U.S. wind engineering practice. The study provides data depicting variabilityrnof wind speeds, wind velocity profiles for a major thunderstorm event and a northeaster, and the influencernof thunderstorms on annual extreme wind speeds at various heights above ground in a typical roughrnenvironment. Data showing the decrease in the power law exponent with increasing wind speed is alsornpresented. It is demonstrated that near-ground wind speeds (i.e., less than 10 m above ground) are likelyrnto be over-estimated in the current design practice by as much as 20 percent which may result in windrnload over-estimate of about 50% for low-rise buildings in typical rough terrain. The importance ofrnthunderstorm wind profiles on determination of design wind speeds and building loads (particularly forrnbuildings substantially taller than 10 m) is also discussed. Recommendations are given for possiblernimprovements to the current design practice in the United States with respect to low-rise buildings inrnrough terrain and for the need to study the impact of thunderstorm gust profile shapes on extreme valuernwind speed estimates and building loads.
Key Words
wind velocity profile; power law; near-ground wind characteristics; wind engineering; extreme value; thunderstorms; shielding; exposure; topographic effects; variability.
Abstract
Many practical time series, including pressure signals measured on roof-corners of low-risernbuildings in quartering winds, consist of relatively quiescent periods interrupted by intermittent transients.rnThe dyadic wavelet transform is used to detect these transients in pressure time series and a relativelyrnsimple pattern classification scheme is used to detect underlying structure in these transients. Statisticalrnanalysis of the resulting pattern classes yields a library of signal
Key Words
wavelet transform; transients; detection; classification
Address
Chris L. Pettit, Air Force Research Laboratory, Wright-Patterson AFB, OH 45433-7532, U.S.A.rnNicholas P. Jones and Roger Ghanem, Department of Civil Engineering, The Johns Hopkins University, Baltimore, MD 21218, U.S.A.
Abstract
This paper presents an approach for evaluating directionality effects for both wind speeds andrnwind loads in hurricane-prone regions. The focus of this study is on directional wind loads on low-risernstructures. Using event-based simulation, hurricane directionality effects are determined for an open-terrainrncondition at various locations in the southeastern United States. The wind speed (or wind load)rndirectionality factor, defined as the ratio of the N-year mean recurrence interval (MRI) wind speed (orrnwind load) in each direction to the non-directional N-year MRI wind speed (or wind load), is less thanrnone but increases toward unity with increasing MRI. Thus, the degree of conservatism that results fromrnneglecting directionality effects decreases with increasing MRI. It may be desirable to account for localrnexposure effects (siting effects such as shielding, orientation, etc.) in design. To account for these effectsrnin a directionality adjustment, the factor described above for open terrain would need to be transformed tornother terrains/exposures. A
Key Words
directionality; hurricane; probability; simulation; wind load; wind speed.
Address
Zhigang Huang, Applied Research Associates, Raleigh, NC, U.S.A.rnDavid V. Rosowsky, Forest Products and Civil Engineering, Oregon State University, Corvallis, OR 97331-5751, U.S.A.
Abstract
The possible application of a spatially placed passive tuned liquid column damper system forrnsuppressing coupled lateral-torsional responses of tall buildings is investigated in this paper. The windrnloads acting on rectangular tall buildings are analytically expressed as 3-D stochastic model. Meanwhile,rnthe 3-D responses of tall buildings may be coupled due to eccentricities between the stiffness and massrncenters of the buildings. In these cases, torsional responses of the buildings are rather larger, and a TLCDrnsystem composed of several TLCD located near the sides of the buildings is more effective than the samernTLCD placed at the building center in reducing both translational and torsional responses of the buildings.rnIn this paper, extensive analytical and numerical work has been done to present the calculation methodrnand optimize the parameters of such TLCD systems. The numerical examples show that the spatiallyrnplaced TLCD system can reduce coupled along-wind, across-wind and torsional responses significantlyrnwith a fairly small mass ratio.
Key Words
tall building; wind loads; coupled responses; control; TLCD
Address
Shuguo Liang, Department of Civil Engineering, Wuhan University of Hydraulic and Electrical Engineering, Wuhan 430072, P.R. ChinarnQiusheng Li, Department of Building and Construction, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, P.R. ChinarnWeilian Qu, Department of Civil Engineering, Wuhan University of Technology,rnWuhan 430070, P.R. China
Abstract
The Strouhal number is an important nondimensional number which is explanatory ofrnaerodynamic instability phenomena. It takes on the different characteristic constant value depending uponrnthe cross-sectional shape of the body being enveloped by the flow. A number of investigations into thisrnsubject, especially on the drag test, surface pressure test and hot-wire test, have been carried out under thernfixed state of the body in the past. However, almost no investigations concerning the determination of thernSt on wind-induced vibration of the body have been reported in the past even though the aerodynamicrnbehavior of the body is very important because the construction of wind-sensitive structures is recently onrnthe sharp increase. Based on a series of wind tunnel tests, this paper addresses a new method to determine thernStrouhal number of rectangular cylinder in the uniform flow. The central idea of the proposed method isrnthat the Strouhal number can be obtained directly by the aerodynamic behaviors of the body throughrnwind-induced vibration test. The validity of proposed method is evaluated by comparing with the resultsrnobtained by previous studies in three B/Ds at attack angle 0 o and a square cylinder with various attackrnangles. The values and trends of the proposed Strouhal numbers are in good agreements with values ofrnprevious studies. And also, the Strouhal numbers of B/D = 1.5 and 2.0 with various attack angles arernobtained by the proposed method and verified by other method. This proposed method is as good as anyrnother previous methods to obtain the Strouhal number.
Key Words
determination of the Strouhal number.
Address
Chang Koon Choi, Department of Civil Engineering, Korea Advanced Institute of Science and Technology(KAIST), 373-1 Kusong-dong, Yusong-gu, Taejon 305-701, KorearnDae Kun Kwon, Department of Civil Engineering, KAIST, Korea
