H.F. Xiang

Tsing Ma bridge deck under skew winds—Part II: flutter derivatives

The six static aerodynamic coefficients of the Tsing Ma suspension bridge deck under skew winds have been discussed in detail in the companion paper. This paper addresses the measurement of eight flutter derivatives of a typical oblique strip of the Tsing Ma bridge deck under skew winds. The wind tunnel test technique developed for this measurement includes the design of oblique sectional model, the development of a dynamic test rig, and the application of unifying least-square (ULS) method for identification. The eight identified flutter derivatives of discrete values are first fitted to obtain eight flutter derivative curves as functions of both wind inclination and yaw angle. Based on these curves, the effects of wind inclination and yaw angle on aeroelastic damping and stiffness, in particular on critical wind speed, are then discussed. Furthermore, the measured flutter derivatives of the bridge deck under skew winds are compared with those obtained from the empirical formulae derived from the skew wind theory. Finally, the critical wind speeds from the measured flutter derivative A2* curves are also compared with those from the A2* curves estimated by the empirical formulae.

Tsing Ma bridge deck under skew winds—Part I: Aerodynamic coefficients

Abstract This paper aims to measure six static aerodynamic coefficients, while a companion paper addresses the measurement of eight flutter derivatives, of a typical oblique strip of the Tsing Ma suspension bridge deck under skew winds. The wind tunnel test technique developed for the aerodynamic coefficient measurement includes the design of oblique sectional models, the development of a test rig and a measurement system, and the analysis of test results. The effects of model end angle on the aerodynamic coefficients are investigated and found to be very small on lift, drag and pitching moment coefficients. The measured results are then fitted to obtain the six aerodynamic coefficient curves as functions of both wind inclination and yaw angle, which will be used in a later comparison of buffeting response of the bridge between field measurement and analysis. The measurement results reveal that the drag, lift and pitching moment coefficients are much larger than the crosswind force, rolling moment and yawing moment coefficients. The variation of lift coefficient with wind yaw angle is small, but the value of drag coefficient decreases with increasing wind yaw angle and the value of pitching moment coefficient increases with increasing wind yaw angle. The obtained six aerodynamic coefficient curves are also used to examine the currently used cosine rule for buffeting analysis of a bridge under yaw winds. It is found that the traditional cosine rule is generally inadequate, particularly in the cases of large wind yaw angle.

Investigation and prevention of deck galloping oscillation with computational and experimental techniques

Abstract Although bridge aerodynamics usually involves such kinds of wind-induced responses as vortex shedding excitation, buffeting and flutter instability, a bluff cross section for even a short-span bridge, combined with a lightweight superstructure in reality, has brought its galloping-type instability as an important issue for bridge aerodynamics. This paper focuses its attention on the galloping-type oscillation taking as an example of the Yadagawa Bridge in Nagoya, Japan. The deck galloping oscillation of this continuous beam bridge has been thoroughly investigated by CFD computational estimation and wind-tunnel experimental confirmation using a sectional model and an aeroelastic model. Three aerodynamic preventive means, including the 40% slotted deck, the 80% slotted deck and the structure with aerodynamic deflectors, have been suggested and studied to improve the galloping characteristics of the bridge deck.

State-of-the-Art on long-span bridge aerodynamics in China

The State-of-the-Art on long-span bridge aerodynamics in China is presented in this paper with an emphasis on three aspects: contributions in the development of aerodynamic theories, probability-based assessment method in evaluating bridge aerodynamics, and aerodynamic vibration control. The theoretical development discussed in this paper comprises the full-mode flutter analysis method, some new findings in flutter mechanism and stabilization as well as Computational Fluid Dynamics techniques and application. A series of probabilistic assessment approaches is then proposed and applied in wind induced vibration investigation including flutter instability, buffeting response and vortex-induced vibration. The final aspect focuses on the aerodynamic vibration control of long span bridges experienced in China.

Wind-Induced Damages to a Three-Span, Continuous, Concrete Arch Bridge under Construction

The second Yibin bridge is a three-span, continuous, reinforced concrete arch bridge with equal span lengths of 160 m. After two reinforced concrete (RC) ribs were constructed through all three spans, during the night of June 7, 1997, the central span and the side span near Zigong city were found to have collapsed into the river on its own. The remaining side span near Yibin city collapsed later on its own, on August 29, 1997. The aeroelastic and aerodynamic investigations, including definition of design wind speed, determination of aeroelastic and aerodynamic wind loading, testing of wind-induced vibrations, evaluation of RC arch rib strength, were conducted to identify the reason for the collapse. It was finally concluded that aerodynamic instability, flutter or galloping, should be excluded in these two accidents, and the direct reason was the ultimate resistance of the cross-sections at the arch bases being less than the total load response under the joint action of structural dead loads and wind-induced loads including aerodynamic wind loading, aeroelastic wind loading and the loading based on P-Δ effects which were not considered in the design of the bridge under construction.

Nonlinear Aerodynamic Forces on Bridge Decks due to Transverse Sinusoidal Fluctuation of Wind

The aerodynamic forces on bridge decks generated by transverse sinusoidal fluctuation of wind are investigated by 2-dimesional lattice Boltzmann method. The aerodynamic admittance functions in traditional buffeting force model are identified. The proposed numerical method is verified by comparing the corresponding identified admittance functions of a thin flat-plate with the Sears function. The longitudinal buffeting forces of all the four typical decks simulated here have multiple-frequency phenomenon. The transverse buffeting force and buffeting torque of the blunt п-shape deck also have this nonlinear characteristic. A nonlinear buffeting forces model is proposed to reproduce the nonlinear aerodynamic force due to the transversely fluctuating wind.