Techno Press
Tp_Editing System.E (TES.E)
Login Search


was
 
CONTENTS
Volume 4, Number 5, October 2001
 

Abstract
Wind tunnel tests were conducted on a model of deck section from the Ting Kau cablernstayed bridge. The purpose of the tests was to determine the set of aerodynamic derivatives conventionallyrnused to describe the motion-induced forces arising from the wind flow, and to investigate the stability ofrnthe deck under different conditions of turbulence and angle of attack. The study shows that except forrnlarge negative angles of attack the deck section itself is stable up to a high wind speed, and that whenrninstability does occur it is essentially a single degree of freedom (torsional) flutter.

Key Words
cable-stayed bridge; wind tunnel; section model; flutter derivatives.

Address
James Mark William Brownjohn and Cheong Chuen Choi, School of Civil and Structural Engineering, Nanyang Technological University, 50 Nanyang Avenue,rnSingapore 639798, Singapore

Abstract
The paper describes the results of the monitoring of an elevated steel water-tank with unusualrnshape, 85 m high and 40 m wide. The research was carried out analysing both the static and dynamicrnbehaviour under wind actions. The instruments used (some of which were employed for the first time forrnthis project) are described and the data processing procedures are discussed. Comparison between thernexperimental results and those obtained through a numerical model gives interesting information both onrnthe structural behaviour and on the characterisation of wind actions.

Key Words
wind effects; modal identification; monitoring; experimental tests.

Address
Vincenzo Sepe and Antonino E. Zingali, Dipartimento di Ingegneria Strutturale e Geotecnica, Universita di Roma \"La Sapienza\", via Eudossiana 18, 00184 Roma, Italy

Abstract
Simultaneous pressure and force measurements have been conducted on a stationary boxrndeck section model for two configurations (namely without and with New Jersey traffic barriers) atrnvarious angles of incidence. The mean and fluctuating aerodynamic coefficients and pressure coefficientsrnwere derived, together with their spectra and with the coherence functions between the pressures and therntotal aerodynamic forces. The mean aerodynamic coefficients derived from force measurements are firstrncompared with those derived from the integration of the pressures on the deck surface. Correlationrnbetween forces and local pressures are determined in order to gain insight on the wind excitationrnmechanism. The influence of the angle of incidence on the pressure distribution and on the fluctuatingrnforces is also analysed. It is evidenced how particular deck section areas are more responsible for thernaerodynamic excitation of the deck.

Key Words
bridge aerodynamics; aerodynamic forces; wind tunnel testing; pressure measurement.

Address
Francesco Ricciardelli, Department of Mechanics and Materials, University of Reggio Calabria, Via Graziella, Feo di Vito, 89060 Reggio Calabria, ItalyrnHoria Hangan, The Boundary Layer Wind Tunnel Laboratory, The University of Western Ontario, London, Ontario, N6A 5B9, Canada

Abstract
This paper presents an extensive analysis of unsteady wind loading data on a 18 m long andrn2 m high wall in a rural environment, with the wind at a range of angles to the wall normal. The data isrnfirstly analyzed using standard statistical techniques (moments of probability distributions, auto- and cross-correlations,rnauto- and cross-spectra etc.). The analysis is taken further using a variety of less conventionalrnmethods - conditional sampling, proper orthogonal decomposition and wavelet analysis. It is shown that,rneven though the geometry is simple, the nature of the unsteady flow is surprisingly complex. The fluctuatingrnpressures on the front face of the wall are to a great extent caused by the turbulent fluctuations in thernupstream flow, and reflect the oncoming flow structures. The results further suggest that there are distinctrnstructures in the oncoming flow with a variety of scales, and that the second order quasi-steady approachrncan predict the pressure fluctuations quite well. The fluctuating pressures on the rear face are alsorninfluenced by the fluctuations in the oncoming turbulence, but also by unsteady fluctuations due to wakernunsteadiness. These fluctuations have a greater temporal and spatial coherence than on the front face andrnthe quasi-steady method over-predicts the extent of these fluctuations. Finally the results are used to checkrnsome assumptions made in the current UK wind loading code of practice.

Key Words
unsteady loading; correlations; proper orthogonal decomposition; wavelet analysis; conditional sampling; wall.

Address
C. J. Baker, School of Civil Engineering, The University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.

Abstract
Conical vortices on roof corners of a prismatic low-rise building have been investigated by using the PIV(Particle Image Velocimetry) technique. The Reynolds number based on the free stream velocity and model height was 5.3  10 3 . Mean and instantaneous vector fields for velocity, vorticity, and turbulent kinetic energy were measured at two vertical planes and for two different flow angles of 30 o and 45 o . The measurements provided a clear view of the complex flow structures on roof corners such as a pair of counter rotating conical vortices, secondary vortices, and tertiary vortices. They also enabled accurate and easy measurement of the size of vortices. Additionally, we could easily locate the centers of the vortices from the ensemble averaged velocity fields. It was observed that the flow angle of a 30 o produces a higher level of vorticity and turbulent kinetic energy in one of the pair of vortices than does the 45 o flow angle.

Key Words
PIV(Particle Image Velocimetry); conical vortices; wind tunnel measurement; instantaneous and ensemble averaged velocity; vorticity and turbulent kinetic energy.

Address
Kyung Chun Kim , Ho Seong Ji and Seung Hak Seong, School of Mechanical Engineering, Pusan National University, San 30, Jangjeon-Dong, Kumjung-Ku, Pusan 609-735, Korea


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2017 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: info@techno-press.com