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CONTENTS
Volume 15, Number 5, September 2012
 

Abstract
Atmospheric boundary layer winds experience two types of effects due to friction at the ground surface. One effect is the increase of the wind speeds with height above the surface. The second effect, called the Ekman layer effect, entails veering - the change of the wind speed direction as a function of height above the surface. In this study a practical procedure is developed within a databaseassisted design (DAD) framework that accounts approximately for veering effects on tall building design.The procedure was applied in a case study of a 60-story reinforced concrete building, which also considered the dependence of veering effects on the orientation of the building. Comparisons are presented between response estimates that do not account for veering, and account for veering conservatively. For the case studied in this paper veering effects were found to be small.

Key Words
building technology; database-assisted design; mean recurrence interval; reinforced concrete; veering

Address
National Institute of Standards and Technology, Gaithersburg, MD, USA

Abstract
Researchers have recently begun using high spatial resolution remote-sensing data, which are automatically captured and georeferenced, to assess damage following natural and man-made disasters, in addition to, or instead of employing the older methods of walking house-to-house for surveys, or photographing individual buildings from an airplane. This research establishes quantitative relationships between the damage states observed at ground-level, and those observed from space using high spatial resolution remote-sensing data, for windstorms, for individual site-built one- or two-family residences (FR12). \"Degrees of Damage\" (DOD) from the Enhanced Fujita (EF) Scale were determined for groundbased damage states; damage states were also assigned for remote-sensing imagery, using a modified version of Womble\'s Remote-Sensing (RS) Damage Scale. The preliminary developed model can be used to predict the ground-level damage state using remote-sensing imagery, which could significantly lessen the time and expense required to assess the damage following a windstorm.

Key Words
damage; remote-sensing; Enhanced Fujita Scale; tornadoes; hurricanes; Katrina; satellite; Super Tuesday

Address
Tanya M. Brown : Insurance Institute for Business and Home Safety, Richburg, South Carolina, United States, Wind Science & Engineering Research Center, Texas Tech University, Lubbock, Texas, United States
Daan Liang: Department of Construction Engineering and Engineering Technology, Texas Tech University, Lubbock,
Texas, United States
J. Arn Womble : Wind Science & Engineering Research Center, Texas Tech University, Lubbock, Texas, United States,
WindForce Associates, Inc., Lubbock, Texas, United States

Abstract
Bridge hanger vibrations have been reported under icy conditions. In this paper, the results from a series of static and dynamic wind tunnel tests on a circular cylinder representing a bridge hanger with simulated thin ice accretions are presented. The experiments focus on ice accretions produced for wind perpendicular to the cylinder at velocities below 30 m/s and for temperatures between -5C and -1C. Aerodynamic drag, lift and moment coefficients are obtained from the static tests, whilst mean and fluctuating responses are obtained from the dynamic tests. The influence of varying surface roughness is also examined. The static force coefficients are used to predict parameter regions where aerodynamic instability of the iced bridge hanger might be expected to occur, through use of an adapted theoretical 3- DOF quasi-steady galloping instability model, which accounts for sectional axial rotation. A comparison between the 3-DOF model and the instabilities found through two degree-of-freedom (2-DOF) dynamic tests is presented. It is shown that, although there is good agreement between the instabilities found through use of the quasi-steady theory and the dynamic tests, discrepancies exist-indicating the possible inability of quasi-steady theory to fully predict these vibrational instabilities.

Key Words
circular cylinder; bridge hangers; ice accretion; wind tunnel tests; aerodynamic instability; low temperatures; quasi-steady aerodynamics

Address
H. Gjelstrup :COWI A/S, Parallelvej 2, 2800 Kgs. Lyngby , Denmark, Department of Civil Engineering, Technical University of Denmark, Building 118, Brovej,
2800 Kgs. Lyngby , Denmark
C.T. Georgakis :Department of Civil Engineering, Technical University of Denmark, Building 118, Brovej,
2800 Kgs. Lyngby , Denmark
A. Larsen: COWI A/S, Parallelvej 2, 2800 Kgs. Lyngby , Denmark

Abstract
In this paper, the method of introducing additional source/sink terms in the turbulence and momentum transport equations was applied to appropriately model the effect of the tree canopy. At first, the new additional source term for the turbulence frequency w equation in the SST k-w model was proposed through theoretical analogy. Then the new source/sink term model for the SST k-w model was numerically verified. At last, the proposed source term model was adopted in the wind environment optimal design of the twin high-rise buildings of CABR (China Academy of Building Research). Based on the numerical simulations, the technical measure to ameliorate the wind environment was proposed. Using the new inflow boundary conditions developed in the previous studies, it was concluded that the theoretically reasonable source term model of the SST k-w model was applicable for modeling the tree canopy flow and accurate numerical results are obtained.

Key Words
wind environment; high-rise building; numerical simulation; SST k-w model; additional source/sink term; optimization design

Address
Yi Yang :State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou, China, Department of Civil and Environmental Engineering, The Hong Kong University of Science and
Technology, Clear Water Bay, Kowloon, Hong Kong, China
Zhuangning Xie : State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou, China
Tim K.T. Tse : Department of Civil and Environmental Engineering, The Hong Kong University of Science and
Technology, Clear Water Bay, Kowloon, Hong Kong, China
Xinyang Jin : Center of Wind Engineering Research, China Academy of Building Research, Beijing, China
Ming Gu: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China



Abstract
Three common medium- rise building forms were physically tested to study their overall wind induced structural response. Emphasis was placed on the torsional response and its correlation with other peak responses. A higher correlation was found between the peak responses than between the general fluctuating parts of the signals. This suggests a common mechanism causing the peak event, and that this mechanism is potentially different to the mechanism causing the general load fluctuations. The measurements show that about 80% of the peak overall torsion occur simultaneously with the peak overall along wind drag for some generic building shapes. However, the peak torsional response occurs simultaneously with only 30%-40% of the peak overall drag for the rectangular model. These results emphasise the importance of load combinations for building design, which are often neglected in the design of medium sized rigid buildings for which the along-wind drag is dominant. Current design wind loading standards from around the world were evaluated against the results to establish their adequacy for building design incorporating wind-induced torsion effects. Although torsion is frequently neglected, for some structural systems it may become more important.

Key Words
torsion; wind loading; structural response; medium rise building; correlation; design standards

Address
D.C. Keast :Arup Group, Cairns, Australia
A. Barbagallo :School of Civil Engineering, The University of Sydney, Australia
G.S. Wood: Cermak Peterka Petersen Pty. Ltd., Australia

Abstract
This article presents theoretical investigations on techniques for the improvement of the dynamic characteristics of slender bridges under wind action. Aerodynamically effective control shields are applied as controlled actuators. The first part of the article describes the modelling of the uncontrolled aeroelastic system. Acting aerodynamic forces are consistently characterised using linear time-invariant transfer elements in terms of rational functions. On this basis, two configuration levels of the uncontrolled system are represented with linear time-invariant state-space models and investigated. The second part of the article addresses controller design and the behaviour of the controlled aeroelastic system. Both fundamental limits for stabilisation and the efficiency for attenuating the influence of gusts are described for different actuator mechanisms. The results are derived and discussed with methods of control theory.

Key Words
bridges; state-space model; flutter; divergence; active aerodynamic control

Address
Arno Kirch and Udo Peil :Institute of Steel Structures, Technische Universitat Carolo-Wilhelmina zu Braunschweig,
Beethovenstrasse 51, 38106 Braunschweig, Germany


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