Parametric studies on relationships between flutter derivatives of slender bridge(Ⅱ)

Based on curve fitting of coefficients of three component forces of the Messina Straits Bridge, and the previously proposed semi-analytical expressions of flutter derivatives of flexible structure, the change of flutter derivatives of slender bridge cross-section with respect to its aerodynamic center, rotational speed and angle variation is studied using a parametric method. The calculated results are compared with the measured ones, and expressions of flutter derivatives of the Messina Straits Bridge are derived. The intrinsic relationships existing in flutter derivatives are validated again. It is shown that the influence of the rotational speed on flutter derivatives is not negligible. Therefore, it provides an additional semi-analytical approach for analyzing flutter derivatives of the bridge with streamlined cross-section to get its aerodynamic information.

Parametric studies on relationships between flutter derivatives of slender bridge (Ⅰ)

Relationships between flutter derivatives of slender bridge are investigated based on our previously proposed semi-analytical flutter derivatives of flexible structure. The intrinsic relations are validated with test data of flutter derivatives of two bridges. Changes in flutter derivatives with the aerodynamic center, rotation speed, and angle variation are also studied by using a parametric method. The results show correctness of the proposed expressions of flutter derivatives given by authors in Ref. [1], and indicate that certain relations exist between these derivatives. It is also shown that semi-analytical flutter derivatives are applicable to bridges with a streamlined cross-section.

Comparisons of bridges flutter derivatives and generalized ones

The causes of the nonlinearity of self-excited aerodynamic force of bridge are interpreted from such two aspects as amplitude and wind velocity.The concept of"generalized flutter derivative"is proposed,and its physical meaning is illustrated.The graphs of the general-ized flutter derivatives of plate and Sutong Bridge section model are plotted.The characteristics of all generalized flutter derivatives are compared and analyzed,and their superiorities are verified.The results indicate that the physical meaning of generalized flutter derivatives are more explicit compared to the traditional ones.It is more convenient to understand the nonlinearity properties of self-excited aerodynamic force of bridge according to the generalized flutter derivatives graphs with the wind velocity as the horizontal coordinate.

Time-domain and frequency-domain approaches to identification of bridge flutter derivatives

Flutter derivatives are essential for flutter analysis of long-span bridges,and they are generally identified from the vibration testing data of a sectional model suspended in a wind tunnel.Making use of the forced vibration testing data of three sectional models,namely,a thin-plate model,a nearly streamlined model,and a bluff-body model,a comparative study was made to identify the flutter derivatives of each model by using a time-domain method and a frequency-domain method.It was shown that all the flutter derivatives of the thin-plate model identified with the frequency-domain method and time-domain method,respectively,agree very well.Moreover,some of the flutter derivatives of each of the other two models identified with the two methods deviate to some extent.More precisely,the frequency-domain method usually results in smooth curves of the flutter derivatives.The formulation of time-domain method makes the identification results of flutter derivatives relatively sensitive to the signal phase lag between vibration state vector and aerodynamic forces and also prone to be disturbed by noise and nonlinearity.

LINEAR AND NONLINEAR AERODYNAMIC THEORY OF INTERACTION BETWEEN FLEXIBLE LONG STRUCTURE AND WIND

In light of the characteristics of the interactions between flexible structure and wind in three directions, and based on the rational mechanical section-model of structure, a new aerodynamic force model is accepted, i.e, the coefficients of three component forces are the functions of the instantaneous attack angle and rotational speed C-t = C-t (beta(t), 0). (i = D, L, M). So, a new method to formulate the linear and nonlinear aerodynamic items of wind and structure interacting has been put forward in accordance with 'strip theory' and modified 'quasi-static theory', and then the linear and nonlinear coupled theory of super-slender structure for civil engineering analyzing are converged in one model, For the linear aerodynamic-force parts, the semi-analytical expressions of the items so-called 'flutter derivatives' corresponding to the one in the classic equations have been given here, and so have the nonlinear parts. The study of the stability of nonlinear aerodynamic-coupled torsional vibration of the old Tacoma bridge shows that the form and results of the nonlinear control equation in rotational direction are in agreement with that of V. F. Bohm's.

Aerodynamic problems of cable-stayed bridges spanning over one thousand meters

The elongating of cable-stayed bridge brings a series of aerodynamic problems. First of all,geometric nonlinear effect of extreme long cable is much more significant for cable-stayed bridge spanning over one thousand meters. Lateral static wind load will generate additional displacement of long cables,which causes the decrease of supporting rigidity of the whole bridge and the change of dynamic properties. Wind load,being the controlling load in the design of cable-stayed bridge,is a critical problem and needs to be solved. Meanwhile,research on suitable system between pylon and deck indicates fixed-fixed connection system is an effective way for improvement performance of cable-stayed bridges under longitudinal wind load. In order to obtain aerodynamic parameters of cable-stayed bridge spanning over one thousand meters,identification method for flutter derivatives of full bridge aero-elastic model is developed in this paper. Furthermore,vortex induced vibration and Reynolds number effect are detailed discussed.

Investigation of Turbulence Effects on the Aeroelastic Properties of a Truss Bridge Deck Section

This paper presents the flutter derivatives （FDs） extracted from a stochastic system identification （SSI） method under different turbulent flows, The objective of the study is to investigate the effects of oncoming turbulence on the flutter of suspended long-span bridges using a section model wind-tunnel test, Several wind-tunnel tests were performed on a truss bridge deck section with different oncoming turbulent properties involving reduced turbulence intensities and turbulent scales. This study includes an investigation of the effect of oncoming flows on modal dynamic responses. The transient and buffeting response data from the wind-tunnel test are analyzed using the system identification technique in extracting FDs, and the difficulties involved in this method are discussed. The time-domain SSI is applied to extract all FDs simultaneously from one and two degree-of-freedom （1DOF and 2DOF） systems, Finally, the results under different conditions are discussed and conclusions are formed.