Haifan Xiang

Identification of 18 flutter derivatives of bridge decks

Abstract An identification method has been developed to extract all the flutter derivatives defined by R.H. Scanlan. In the present work, the signals of the coupled vertical–torsional free vibration of the spring-suspended section model are used. The flutter derivatives of a thin plate obtained using the present method are compared with the corresponding Theodorsen theoretical values. The present method is then used in the identification of flutter derivatives of the Jiangyin suspension Bridge over Yangtze River. The flutter critical wind speed of this bridge obtained from the full bridge aeroelastic model test in a wind tunnel shows good agreement with the estimated result from Scanlans flutter analysis method with the flutter derivatives using the present method.

Increase of critical flutter wind speed of long-span bridges using tuned mass dampers

Abstract In this paper increasing the critical flutter wind speed of long-span bridges by using tuned mass dampers (TMDs) is theoretically and experimentally studied. Equations governing the motions of a bridge with TMDs are established. The Routh-Hurwitz stability criterion is used to study the aerodynamic instability of the bridge based on the characteristic equation of the system of the bridge and TMDs. A sectional model wind-tunnel test on the Tiger Gate Bridge, a suspension bridge with a steel box deck and a center span of 888 m, is carried out to confirm the numerical results. Some new findings from the test and the calculation are presented.

Coupled flutter analysis of long-span bridges by multimode and full-order approaches

Abstract The coupled flutter problem of long-span bridges is addressed in this paper. Firstly, a multimode flutter analysis is proposed based on Scanlans linear self-excited forces. The proposed multimode method is single-parameter, non-iterative and offers simplicity, automaticity and robustness. Secondly, a new full-order analysis for the flutter problem is developed. The presented full-order method overcomes partly the defects of the previous direct flutter analysis and is also single-parameter and efficient. Since any assumption is not included on computation, the full-order method is a strict and accurate flutter analysis from the viewpoint of methodology. Moreover, the coupled flutter analysis of the Jiangyin Yangtse River Suspension Bridge with 1385m-long main span is performed.

Refinements on aerodynamic stability analysis of super long-span bridges

Abstract The traditional flutter and buffeting analysis method essentially established by Professors Scanlan and Davenport is mainly based on undeformed structures and linear theory. But for super long-span bridges, the influences of basic hypothesis in the conventional theory might be unnegligible factors of aerodynamic performance, and some prospective refinements on aerodynamic stability analysis should be considered. These refinements include nonlinear effects of deformed structures, influence of full-coupled flutter derivatives, full-mode flutter analysis, probabilistic assessment of the onset of flutter and computational fluid dynamics application in aerodynamic analysis as well. The comparison and contrast between the results obtained from traditional approaches and refined ones have shown the importance and rationality, while analyzing the aerodynamic performance of super long-span bridges. All of these refinements have significantly helped to understand how a super long-span bridge behaves in aerodynamic and aeroelastic performance.

Alongwind static equivalent wind loads and responses of tall buildings. Part I: Unfavorable distributions of static equivalent wind loads

Abstract Although on the same theoretical basis, the current standards of major countries have set out two evidently different distributions of alongwind static equivalent wind loads, one being the same as the mean wind force and the other the same as the first mode shape on tall buildings. In this paper, the fluctuating static equivalent wind load is evaluated as mean, background and resonant components, and the unfavorable distribution of each component is separately addressed. Meanwhile, the wind loads by the above two code methods are derived. The effects of the wind loads by the two code methods on tall buildings are then examined to identify whether or not they are equivalent with regard to the actual wind induced responses. The results show that the wind loads by the two code methods can only ensure an equivalent first mode displacement response, and they may lead to some considerably unfavorable load effects, for example, the base shear force estimation. Finally a numerical example demonstrating the main results is given.

A practical method of passive TMD for suppressing wind-induced vertical buffeting of long-span cable-stayed bridges and its application

Abstract Formulas for the reduction ratio of tuned mass dampers (TMD) for suppressing the wind-induced vertical buffeting response of long span bridges and the optimal solutions of the parameters of TMD for engineering purposes are derived. The accuracy of the formulas relevant to the design of TMD is confirmed. An aeroelastic test of a full model of the Yangpu Bridge with and without TMD was done, and it was found that the results for the reduction ratio obtained from the test were in good agreement with those from the formulae. Some meaningful results are obtained from the detailed analysis. In addition, “TMD design wind speed” and the constraint conditions are further stressed and discussed. Finally, the Yangpu Bridge is taken as an example to show the application of these formulae.

Optimization of TMD for suppressing buffeting response of long-span bridges

Abstract A mathematical model is developed for optimizing the parameters of TMD (tuned mass damper) used for suppressing buffeting response of long-span bridges. The parameters of the TMD with which Nanpu Cable-Stayed Bridge under construction in Shanghai, China, is suggested to be equipped are calculated by using the computer program made by the authors based on the method.

Alongwind static equivalent wind loads and responses of tall buildings. Part II: Effects of mode shapes

Abstract The reconsideration of the alongwind responses of tall buildings in part I is continued in the present paper. According to the literature to date, the effects of mode shape on the alongwind responses of tall buildings are taken to be negligible. In this paper, it is pointed out that only the effect of the first-mode displacement response has been included in the previous literature. Closed form expressions for the mode-shape correction are provided. The factor for the first-mode displacement response is in good agreement with that in the literature, and it can be neglected; but the factors for some other wind-induced responses, such as the base shear force, cannot be neglected. Finally a new correction procedure, which provides directly the static equivalent wind load, is developed.

Statistical study for mean wind velocity in Shanghai area

Abstract In order to predict mean wind velocity in the Shanghai area, the probability distribution model of extreme values has been used in the statistical analysis of joint distribution of wind speed and corresponding direction in this paper. The theoretical model of the joint probability distribution with directional independent coefficients is set up to describe joint distribution of wind speed and direction, and its application method is developed into three statistical steps, data processing of wind speed records, examination of joint distribution model and estimation of distribution model parameters. These application methods have been used to calculate extreme wind velocity in the surface measurement stations, Baoshan, Chuansha and Longhua, and at the deck level of the Yangpu Bridge in Shanghai.

An introduction to the Chinese wind-resistant design guideline for highway bridges

Abstract Some main comments upon the Chinese Wind Resistant Design Guideline for Highway Bridges are explained. The determination of bridge design wind speeds, the calculation of wind loads including the static part and dynamic part, some empirical formulas for basic frequency estimation of cable-stayed bridges and suspension bridges, critical flutter wind speed estimation at the preliminary design stage of bridges and the response spectrum method for estimating the buffeting response of bridges after completion are introduced.