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


was
 
CONTENTS
Volume 12, Number 5, August 2009
 

Abstract
A method is applied for the estimation of structural damage of tall slender structures using natural frequency and displacements measurements by GPS. The relationship between the variation in the global stiffness matrix (or in the stiffness of each finite element) and the change in the natural frequencies of the structure is given. In engineering practice the number of frequencies which can be derived by GPS measurement of long-period structures will be equal to one, two or three first natural frequencies. This allows us in initial studies to detect damage with frequency changes based on forward methods in which the measured frequencies are compared with the predicted analytical data. This idea, of health monitoring from possible changes to natural frequencies, or from a statement of excessive displacements is applied to the Stuttgart TV Tower.

Key Words
full-scale measurements; GPS; monitoring; the Stuttgart TV Tower; wind.

Address
Tadeusz Chmielewski; Opole University of Technology, ul. Katowicka 48, 45-061 Opole, Poland
Peter Breuer; University of Applied Sciences, Schellingstrasse 24, 70174 Stuttgart, Germany
Piotr Gorski; Opole University of Technology, ul. Katowicka 48, 45-061 Opole, Poland
Eduard Konopka; University of Applied Sciences, Schellingstrasse 24, 70174 Stuttgart, Germany

Abstract
A series of wind tunnel free-decay sectional model dynamic tests were conducted to examine the effects of torsional-to-vertical natural frequency ratio of 2DOF bridge dynamic systems on the aerodynamic and dynamic properties of bridge decks. The natural frequency ratios tested were around 2.2:1 and 1.2:1 respectively, with the fundamental vertical natural frequency of the system held constant for all the tests. Three 2.9 m long twin-deck bridge sectional models, with a zero, 16% (intermediate gap) and 35% (large gap) gap-to-width ratio, respectively, were tested to determine whether the effects of frequency ratio are dependent on bridge deck cross-section shapes. The results of wind tunnel tests suggest that for the model with a zero gap-width, a model to approximate a thin flat plate, the flutter derivatives, and consequently the aerodynamic forces, are relatively independent of the torsional-to-vertical frequency ratio for a relatively large range of reduced wind velocities, while for the models with an intermediate gap-width (around 16%) and a large gap-width (around 35%), some of the flutter derivatives, and therefore the aerodynamic forces, are evidently dependent on the frequency ratio for most of the tested reduced velocities. A comparison of the modal damping ratios also suggests that the torsional damping ratio is much more sensitive to the frequency ratio, especially for the two models with nonzero gap (16% and 35% gap-width). The test results clearly show that the effects of the frequency ratio on the flutter derivatives and the aerodynamic forces were dependent on the aerodynamic cross-section shape of the bridge deck.

Key Words
wind-induced vibration; flutter derivative; system identification; frequency ratio; wind tunnel test.

Address
X.R. Qin, K.C.S. Kwok, C.H. Fok and P.A. Hitchcock
; CLP Power Wind/Wave Tunnel Facility, HKUST, H.K. S.A.R. P.R. China

Abstract
The expediency of revising universal rules for the combination of gravity and lateral actions of wind force-resisting steel structures recommended by the Standards EN 1990 and ASCE/SEI 7-05 is discussed. Extreme wind forces, gravity actions and their combinations for the limit state design of structures are considered. The effect of statistical uncertainties of extreme wind pressure and steel yield strength on the structural safety of beam-column joints of wind force-resisting multistory steel frames designed by the partial factor design (PFD) and the load and resistance factor design (LRFD) methods is demonstrated. The limit state criterion and the performance process of steel frame joints are presented and considered. Their long-term survival probability analysis is based on the unsophisticated method of transformed conditional probabilities. A numerical example illustrates some discrepancies in international design standards and the necessity to revise the rule of universal combinations of loads in wind and structural engineering.

Key Words
wind engineering; wind-resisting frames; wind forces; combinations of actions; beam-column joints; structural safety.

Address
Antanas Kudzys and Algirdas Kudzys; KTU Institute of Architecture and Construction, Tunelio 60, 44405 Kaunas, Lithuania

Abstract
Studying the spatial distribution in coherent fields such as turbulence and turbulence-induced force is important to model and evaluate turbulence-induced forces and response of structures in the turbulent flows. Turbulence field-based coherence function is commonly used for the spatial distribution characteristic of the turbulence-induced forces in the frequency domain so far. This paper will focus to study spectral coherent structure of the turbulence and induced forces in not only the frequency domain using conventional Fourier transform-based coherence, but also temporo-spectral coherence one in the time-frequency plane thanks to wavelet transform-based coherence for better understanding of the turbulence and force coherences and their spatial distributions. Effects of spanwise separations, bluff body flow, flow conditions and Karman vortex on coherent structures of the turbulence and induced pressure, comparison between turbulence and pressure coherences as well as intermittency of the coherent structure in the time-frequency plane will be investigated here. Some new findings are that not only the force coherence is higher than the turbulence coherence, the coherences of turbulence and forces depend on the spanwise separation as previous studies, but also the coherent structures of turbulence and forces relate to the ongoing turbulence flow and bluff body flow, moreover, intermittency in the time domain and low spectral band is considered as the nature of the coherent structure. Simultaneous measurements of the surface pressure and turbulence have been carried out on some typical rectangular cylinders with slenderness ratios B/D=1 (without and with splitter plate) and B/D=5 under the artificial turbulent flows in the wind tunnel.

Key Words
coherent structure; spanwise coherence; wind turbulence; surface pressure; continuous wavelet transform; wavelet coherence; time-frequency analysis.

Address
Thai-Hoa Le; Department of Engineering Mechanics and Automation, Vietnam National University, Hanoi 144 Xuan Thuy, Cau Giay, Hanoi, Vietnam
Masaru Matsumoto and Hiromichi Shirato; Department of Civil and Earth Resources Engineering, Kyoto University, Kyoto-Daigaku-Katsura Campus, Nishikyo-ku, Kyoto 611-8540, Japan

Abstract
Techniques for stabilising slender bridges under wind loads are presented in this article. A mathematically consistent description of the acting aerodynamic forces is essential when investigating these ideas. Against this background, motion-induced aerodynamic forces are characterised using a linear time-invariant transfer element in terms of rational functions. With the help of these functions, the aeroelastic system can be described in the form of a linear, time-invariant state-space model. It is shown that the divergence wind speed constitutes an upper bound for the application of the selected mechanical actuators. Even active control with full state feedback cannot overcome this limitation. The results are derived and explained with methods of control theory.

Key Words
bridges; rational function approximation; state-space model; flutter; divergence; active control.

Address
Arno Kirch and Udo Peil; Institute of Steel Structures, Technische Universitat Carolo-Wilhelmina zu Braunschweig, Beethovenstra

Abstract
Currently, the commonly built suspension bridges are single or three-span symmetric structural system. To well suit with the natural conditions, several two-span non-symmetric suspension bridges have been built such as the Tsingma Bridge in Hongkong, the Xihoumen Bridge in China etc. It is well known that the wind stability of suspension bridges during erection becomes a subject of major concern. Up to now, comprehensive investigations on the wind stability of structurally symmetric suspension bridges under erection have been conducted, and some wind stability improvement measures have been proposed. (Cobo del Arco and Aparicio 2001, Ge and Tanaka 2000, Zhang 2004). Unfortunately, few investigations on the wind stability of structurally non-symmetric suspension bridge during erection have been done. The present paper focuses its attention on how the wind stability varies during deck erection, and also attempts to find an optimized erection sequence for a structurally non-symmetric suspension bridge. By taking the world

Key Words


Address
Xin-Jun Zhang; College of Civil Engineering Architecture, Zhejiang University of Technology, Hangzhou 310014, P.R.China


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