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CONTENTS
Volume 6, Number 1, January 2003
 

Abstract
Nowadays balanced cantilever construction plays an essential role as a sophisticated erection technique of bridges due to its economical and ecological advantages. Experience teaches that wind has a great importance with regard to this construction technique, but methods proposed by codes to take wind effects into account are still rather crude and, in most cases, completely lacking. Also research in this field is quite limited and aimed at studying only the longitudinal shear and the torque at the pier base, caused by the mean wind velocity and by the longitudinal turbulence actions over the deck. This paper advances the present solutions by developing a new procedure that takes into account all wind effects both on the deck and on the pier. The proposed model assumes the mean wind velocity as orthogonal to the bridge plane and considers the effects produced by all the three turbulence components and by the vortex shedding. The applications point out the role of each loading component on different bridge configurations and show that disregarding the presence of some effects may imply oversimplified results and relevant underestimations.

Key Words
alongwind vibrations; atmospheric turbulence; bridges; cantilever erection stages; crosswind; vibrations; maximum response; torsional vibrations; vortex shedding; wind engineering; 3D wind-induced effects.

Address
ParsonsrnDepartment of Structural and Geotechnical Engineering, University of Genoa, Italy

Abstract
The steady state response of a torsionally coupled system with tuned mass dampers (TMDs) to external wind-induced harmonic excitation is presented. The torsionally coupled system is considered as oneway eccentric system. The eccentricity considered in the system is accidental eccentricity only. The performance of single tuned mass damper (TMD) optimally designed without considering the torsion is investigated for the torsionally coupled system and found that the effectiveness of a single TMD is significantly reduced due to torsion in the system. However, the design of TMD system without considering the torsion is only justified for torsionally stiff systems. Further, the optimum parameters of a single TMD considering the accidental eccentricity are obtained using numerical searching technique for different values of uncoupled torsional to lateral frequency ratio and aspect ratio of the system. The optimally designed single TMD system is found to be less effective for torsionally coupled system in comparison to uncoupled system. This is due to the fact that a torsionally coupled system has two natural frequencies of vibration, as a result, at least two TMDs are requiredrnwhich can control both lateral and torsional response of the system. The optimum damper parameters of different alternate arrangements such as (i) two identical TMDs placed at opposite corners, (ii) two independent TMDs and (iii) four TMDs are evaluated for minimum response of the system. The comparative performance of the above TMDs arrangements is also studied for both torsionally coupled and uncoupled systems. It is found that four TMDs arrangement is quite effective solution for vibration control of torsionally coupled system.

Key Words
vibration control; wind excitation; harmonic; TMDs; torsional coupling; robustness; accidental eccentricity.

Address
Department of Civil Engineering, Indian Institute of Technology Bombay,rnPowai, Mumbai-400 076, India

Abstract
Rain-wind induced vibrations of cables are a challenging problem in the design of cablestayed bridges. The precise excitation mechanism of the complex interaction between structure, wind and rain is still unknown. A theoretical model that is able to accurately simulate the observed phenomena is not available. This paper presents a mathematical model describing rain-wind induced vibrations asrnmovement-induced vibrations using the quasi-steady strip theory. Both, the vibrations of the cable and the movement of the water rivulet on the cable surface can be described by the model including all geometrical and physical nonlinearities. The analysis using the stability and bifurcation theory shows that the model is capable of simulating the basic phenomena of the vibrations, such as dependence of wind velocity and cable damping. The results agree well with field data and wind tunnel tests. An extensive experimental study is currently performed to calibrate the parameters of the model.

Key Words
rain-wind induced vibration; cable-stayed bridges; guyed mast; cable vibrations; nonlinear dynamics; stability and bifurcation theory.

Address
Graduate College

Abstract
Tsing Ma Bridge in Hong Kong is the longest suspension bridge in the world carrying both highway and railway. It has two H-shape concrete towers, each of which is composed of two reinforced concrete legs and four deep transverse prestressed concrete beams. A series of wind tunnel tests have been performed to measure the aerodynamic coefficients of the tower legs and transverse beams in various arrangements. A 1:100 scaled 3D rigid model of the full bridge tower assembled from various tower components has been constructed for different test cases. The aerodynamic coefficients of the lower and upper segments of the windward and leeward tower legs and those of the transverse beams at different levels, with and without the dummy bridge deck model, were measured as a function of yaw wind angle. The effects of wind interference among the tower components and the influence of the bridge deck on the tower aerodynamicrncoefficients were also investigated. The results achieved can be used as the pertinent data for the comparison of the computed and field-measured fully coupled buffeting responses of the entire bridge under yaw winds.

Key Words
Tsing Ma Bridge; tower leg; tower transverse beam; yaw wind; aerodynamic coefficient; wind tunnel test.

Address
State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University,rn1239 Siping Rd. Shanghai 200092, ChinarnDepartment of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, ChinarnDepartment of Bridge Engineering, Tongji University, 1239 Siping Rd., Shanghai 200092, China

Abstract
In recent years, high-strength, light-weight materials have been widely used in the construction of high-rise buildings. Such structures generally have flexible, low-damping characteristics. Consequently, wind-induced oscillation greatly affects the structural safety and the comfort of the building

Key Words
tuned liquid column damper; aerodynamic damping ratio; wind tunnel experiment; high-rise building.

Address
Department of Civil Engineering, National Central University, Taiwan, R.O.C.


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