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CONTENTS
Volume 2, Number 1, March 1999
 

Abstract
Wind effects are critical considerations in the design of topside structures, overall structural systems, or both, depending on the water depth and type of offshore platform. The reliable design of these facilities for oil fields in regions of hostile environment can only be assured through better understanding of the environmental load effects and enhanced response prediction capabilities. This paper summarizes the analysis and performance of offshore platforms under extreme wind loads, including the quantification of wind load effects with focus on wind field characteristics, steady and unsteady loads, gust loading factors, application of wind tunnel tests, and the provisions of the American Petroleum Institute Recommended Practice 2A - Working Stress Design (API RP 2A-WSD) for the construction of offshore structures under the action of wind. A survey of the performance of platforms and satellite structures is provided, and failure mechanisms concerning different damage scenarios during Hurricane Andrew are examined. Guidelines and provisions for improving analysis and design of structures are addressed.

Key Words
hurricanes; offshore platforms; turbulence; wind loading; building codes; damage; wind speeds; waves.

Address
NatHaz Modelling Laboratory, Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556-0767, U.S.A.rnOffshore Mineral Management, Mineral Management Service, Technology Assessment and Research Branch, Herndon, VA 22070-4817, U.S.A.

Abstract
In this paper, artificial neural networks, a new kind of intelligent method, are employed to model and predict amplitude dependent damping in buildings based on our full-scale measurements of buildings. The modelling method and procedure using neural networks to model the damping are studies. Comparative analysis of different neural network models of damping, which includes multi-layer perception network (MLP), recurrent neural network, and general regression neural network (GRNN), is performed and discussed in detail. The performances of the models are evaluated and discussed by tests and predictions including self-test,

Key Words
full-scale measurement; amplitude dependent damping; artificial neural networks; general regression network; prediction.

Address
Department of Building and Construction, City University of Hong Kong, Tat Chee Ave. Kowloon, Hong Kong

Abstract
The flutter of a bridge is induced by self-exited force factors such as lift, drag and aerodynamic moment. These factors are associated with flutter derivatives in the analysis of wind engineering. The flutter derivatives are the function of structure configuration, wind velocity and response circular frequency. Therefore, the governing equations for the interaction between the wind and dynamic response of the structure are complicated and highly nonlinear. Herein, a numerical algorithm through graphical technique for the solution of wind at flutter is presented. It provides a concise approach to the solution of wind velocity at flutter.

Key Words
flutter; aerodynamic instability; cable-suspended bridges

Address
Department of Civil Engineering, National Chung-Hsing University, Taichung, Taiwan-40227, R.O.C.

Abstract
Applying and extending some preceding researches, this paper proposes a map of Italian extreme winds assigning the reference velocity, i.e., the wind velocity averaged over 10 minutes, at 10m height, in a flat open terrain, with 50 years mean return period, depending on the site and the altitude. Furthermore, an objective criterion is formulated by which the actual values of the local wind velocity are given as a function of the reference velocity. The study has been carried out in view of the revision of the Italian Standards dealing with safety and loads and the introduction of the aeolic Italian map into Eurocode 1.

Key Words
extreme velocity; meteorological station; probabilistic analysis; standards; wind load; wind map.

Address
Department of Structural Engineering, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, ItalyrnDepartment of Structural and Geotechnical Engineering, University of Genova, Via Montallegro 1, 16145 Genova, Italy

Abstract
The most common used control device on tall buildings and high-rise structures is active and passive tuned mass damper (ATMD and TMD). The major advantages of ATMD and TMD are discussed. The existing installations of various passive/active control devices on real structures are listed. A set of parameter optimization methods is proposed to determine optimal parameters of passive tuned mass dampers under wind excitation. Simplified formulas for determining the optimal parameters are proposed so that the design of a TMD can be carried out easily. Optimal design of wind-induced vibration control of frame structures is investigated. A thirty-story tall building is used as an example to demonstrate the procedure and to verify the efficiency of ATMD and TMD with the optimal parameters.

Key Words
optimization, active structural control, tuned mass damper, wind-induced vibration, tall buildings.

Address
Department of Building and Construction, City University of Hong Kong, Hong Kong.rnDepartment of Civil Engineering, State University of New York at Buffalo, USArnDepartment of Civil Engineering, Wuhan University of Technology, China


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