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CONTENTS
Volume 6, Number 4, July 2003
 

Abstract
The purpose of this study is to propose a procedure for evaluating quantitatively the increase of the equivalent damping ratio of a structure with passive/active vibration control systems subjected to a stationary wind load. A Lyapunov function governing the response of a structure and its differential equation are formulated first. Then the state-space equation of the structure coupled with the secondaryrndamping system is solved. The results are substituted into the differential equation of the Lyapunov function and its derivative. The equivalent damping ratios are obtained from the Lyapunov function of the combined system and its derivative, and are used to assess the control effect of various damping devicesrnquantitatively. The accuracy of the proposed procedure is confirmed by applying it to a structure with nonlinear as well as linear passive/active control systems.

Key Words
equivalent damping; wind load; structural control; active/passive dampers.

Address
Jae-Seung Hwang; School of Architecture, Chonnam National University, Gwangju, KorearnJinkoo Kim; Department of Architectural Engineering, Sungkyunkwan University, Suwon, KorearnSang-Hyun Lee; Department of Architecture, Seoul National University Seoul, KorearnKyung-Won Min; Department of Architectural Engineering, Dankuk University, Seoul, Korea

Abstract
This study investigates the effects of a bridge deck's width-to-depth (B/H) ratio and turbulence on buffeting response and flutter critical wind speed of long-span bridges by conducting section model tests. A streamlined box section and a plate girder section, each with four B/H ratios, were tested in smooth and turbulent flows. The results show that for the box girders, the response increases with the B/H ratio, especially in the vertical direction. For the plate girders, the vertical response also increases with the B/H ratio. However, the torsional response decreases as the B/H ratio increases. Increasing the B/H ratio and intensity of turbulence tends to improve the bridge's aerodynamic stability. Experimental results obtained from the section model tests agree reasonably with the calculated results obtained from a numerical analysis.

Key Words
width-to-depth ratio; turbulence; buffeting; flutter; section model; long-span bridge.

Address
Department of Civil Engineering, Tamkang University, Tamsui, Taiwan 251, R.O.C.

Abstract
Flutter stability is one of major concerns on the design of long-span cable-stayed bridges. Considering the geometric nonlinearity of cable-stayed bridges and the effects due to the nonlinear windstructure interactions, a nonlinear method is proposed to analyze the flutter stability of cable-stayed bridges, and a computer program NFAB is also developed. Taking the Jingsha bridge over the YangtzernRiver as example, parametric analyses on flutter stability of the bridge are carried out, and some important design parameters that affect the flutter stability of cable-stayed bridges are pointed out.

Key Words
cable-stayed bridge; design parameters; flutter stability; nonlinear flutter analysis.

Address
Xin-Jun Zhang; Department of Civil Engineering, Zhejiang University of Technology, Hangzhou 310032, ChinarnBing-Nan Sun; Department of Civil Engineering, Zhejiang University, Hangzhou 310027, China

Abstract
Many investigations have been conducted to find out the reason behind wind-rain-induced cable vibration in cable-stayed bridges. A single-degree-of-freedom (SDOF) analytical model, which could capture main features of wind-rain-induced cable vibration, was recently presented by the writers. This paper extends the SDOF model to a 2DOF model by including the equation of motion of upper rivulet. The interaction between the upper rivulet and the cable is described in terms of nonlinear damping force, linear restoring force, and inertia force. The computed results using the 2DOF model are first comparedrnwith the results from simulated wind-rain tunnel tests, and the comparison is found satisfactory in general. The possible mechanisms of wind-rain-induced cable vibration are discussed and a parametric study is then conducted. Finally, the computed results using the 2DOF model are compared with those predicted by thernSDOF model. The 2DOF model is found better than the SDOF model but the SDOF model is still acceptable for its simplicity.

Key Words
stay cable; cable vibration; wind; rain; moving rivulet; SDOF model; 2DOF model; comparison.

Address
Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China

Abstract
The paper presents results of studies concerning wind-induced aeolian vibration and fatigue of a 110 kV covered conductor overhead line. Self-damping measurement techniques are discussed: power method is found to be the most reliable technique. A method for compensating tension variations during thernself-damping test is presented. Generally used empirical self-damping power models are enhanced and the different models are compared with each other. The Energy Balance Analysis (EBA) is used to calculate the aeolian vibration amplitudes, which thereafter are converted to bending stress for the calculation ofrnconductor lifetime estimate. The results of EBA are compared with field measurements. Results indicate that adequate lifetime estimates are produced by EBA as well as field measurements. Generally the EBA gives more conservative lifetime expectancy. This is believed to result from the additional dampingrnexisting in true suspension structures not taken into account by EBA. Finally, the correctness of the line design is verified using Cigre

Key Words
aeolian vibration; transmission line; conductor; lifetime; self-damping; energy balance principle.

Address
Tapio Leskinen; Ensto Utility Networks, POB 51, 06101 Porvoo, FinlandrnKari Kantola; Helsinki University of Technology, POB 4300, 02015 HUT, Finland


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