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CONTENTS
Volume 8, Number 5, September 2005
 

Abstract
Aerodynamic damping often plays an important role in estimations of wind induced dynamic responses of super high-rise buildings. Across- and along-wind aerodynamic damping ratios of a square super high-rise building with a height of 300 m are identified with the Random Decrement technique (RDT) from random vibration responses of the SDOF aeroelastic model in simulated wind fields. Parametric studies on effects of reduced wind velocity, terrain type and structural damping ratio on the aerodynamic damping ratios are further performed. Finally formulas of across- and along-wind aerodynamic damping ratios of the square super high-rise building are derived with curve fitting technique and accuracy of the formulas is verified.

Key Words
super high-rise building; aerodynamic damping; wind induced response; aeroelastic model wind tunnel test.

Address
Yong Quan and Ming Gu; State Key Laboratory Disaster Reduction in Civil Engineering, Tongji University, 1239, Siping Road, Shanghai, 200092, ChinarnYukio Tamura; Department of Architecture, Tokyo Polytechnic University, 1583, Iiyama, Atsugi, Kanagawa, 243-0297, Japan

Abstract
This paper deals with the buckling behavior of thin-walled aboveground tanks under wind load. In order to do that, the wind pressures are obtained by means of wind-tunnel experiments, while the structural non linear response is computed by means of a finite element discretization of the tank. Wind-tunnel models were constructed and tested to evaluate group effects in tandem configurations, i.e. one or two tanks shielding an instrumented tank. Pressures on the roof and on the cylindrical part were measured by pressure taps. The geometry of the target tank is similar in relative dimensions to typical tanks found in oil storage facilities, and several group configurations were tested with blocking tanks of different sizes and different separation between the target tank and those blocking it. The experimental results show changes in the pressure distributions around the circumference of the tank for half diameter spacing, with respect to an isolated tank with similar dimensions. Moreover, when the front tank of the tandem array has a height smaller than the target tank, increments in the windward pressures were measured. From the computational analysis, it seems that the additional stiffness provided by the roof prevents reductions in the buckling load for cases even when increments in pressures develop in the top region of the cylinder.

Key Words
bifurcation; buckling; finite elements; steel tanks; tank farms; wind pressures; wind-tunnel.

Address
Genock Portela; General Engineering Department, University of Puerto Rico, Mayag?ez, Puerto Rico 00681-9044, USArnLuis A. Godoy; Civil Infrastructure Research Center, Department of Civil Engineering and Surveying, University of Puerto Rico, Mayag?ez, Puerto Rico 00681-9041, USA

Abstract
Overhead sign support structures number in the tens of thousands throughout the trunk-line roadways in the United States. A recent two-phase study sponsored by the National Cooperative Highway Research Program resulted in the most significant changes to the AASHTO design specifications for sign support structures to date. The driving factor for these substantial changes was fatigue related cracks and some recent failures. This paper presents the method and results of a subsequent study sponsored by the Michigan Department of Transportation (MDOT) to develop a relative performance-based procedure to rank overhead sign support structures around the United States based on a linear combination of their expected fatigue life and an approximate measure of cost. This was accomplished by coupling a random vibrations approach with six degree-of-freedom linear dynamic models for fatigue life estimation. Approximate cost was modeled as the product of the steel weight and a constructability factor. An objective function was developed and used to rank selected steel sign support structures from around the country with the goal of maximizing the objective function. Although a purely relative approach, the ranking procedure was found to be efficient and provided the decision support necessary to MDOT.

Key Words
overhead sign support; cantilever; fatigue; wind load; steel design.

Address
John W. van de Lindt; Department of Civil Engineering, Colorado State University, Fort Collins, CO 80523-1372, USArnTheresa M. Ahlborn; Civil and Environmental Engineering, Michigan Technological University, Houghton Michigan 49931-1295, USA

Abstract
Mean and extreme pressure distributions on a large cantilevered flat roof model are measured in a boundary layer wind tunnel. The largest peak suction values are observed from pressure taps beneath conical

Key Words
flat roof; wind load; wind tunnel test

Address
J. Y. Fu1,2 and Q. S. Li1; 1Department of Building and Construction, City University of Hong Kong, Kowloon, Hong Kongrn2Department of Civil Engineering, Jinan University, Guangzhou 510632, ChinarnZ. N. Xie; Department of Civil Engineering, Shantou University, Shantou 515063, China

Abstract
Quasi-steady approaches have been often adopted to model wind forces on moving cylinders in cross-flow and to study instability conditions of rigid cylinders supported by visco-elastic devices. Recently, much attention has been devoted to the experimental study of inclined and/or yawed circular cylinders detecting dynamical phenomena such as galloping-like instability, but, at the present state-of-the-art, no mathematical model is able to recognize or predict satisfactorily this behaviour. The present paper presents a generalization of the quasi-steady approach for the definition of the flow-induced forces on yawed and inclined circular cylinders. The proposed model is able to replicate experimental behaviour and to predict the galloping instability observed during a series of recent wind-tunnel tests.

Key Words
quasi-steady modeling; aerodynamic instability; yawed cylinders; galloping.

Address
Dipartimento di Ingegneria Strutturale e Geotecnica, University of Genova, Via Montallegro 1, 16145 Genova, Italy


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