Bridge Section Model Research Articles

Control of vortex shedding-induced effects in a sectional bridge model by spanwise perturbation method

An experimental study was conducted to determine the effectiveness of the spanwise sinusoidal perturbation method (SPPM) in controlling vortex-induced vibrations (VIV) in a plate girder bridge section model. The geometric parameters of the plate girder section model were selected to give the maximum VIV response. A SPPM module was attached to both the leading and trailing edges of the section model. Two different SPPM configurations with two different wavelengths and the same amplitude were utilized. Vertical motion responses, surface pressure measurements, as well as hotwire measurements in the wake of the section model were taken. The results revealed that the SPPM with the higher wave steepness distinctively suppressed the VIV responses. The behavior of the model with the SPPM is remarkably different with a fixed section model. Generally, a reduction in the fluctuating surface pressure components is observed, indicating an increase in the degree of steadiness of the flow around the model with either of the two SPPM configurations. However, no qualitative difference could be observed between the effects of the low and high wave steepness configurations. Moreover, wake measurements did not show any distinctive effect for either configuration when compared to the base case.

Wind tunnel test of an active mass damper for bridge decks

An active mass damper is implemented to a bridge section model test in a wind tunnel to enhance the flutter stability. Servo motors controlling the rotational motion of control masses serve as actuators. The torque generated by rotational acceleration is used to control the angular motion of the section model. The mechanical parameters of the uncontrolled and the controlled structures are identified by the modified Ibrahim time domain (MITD) method. The deterioration of the control performance through control loop time delay is determined. The critical wind speeds are determined experimentally by wind tunnel tests and numerically by flutter analysis. The experimental and numerical results are in good agreement. The experimental results underline the applicability of an active mass damper and can be seen as a first step towards an implementation in real bridges.

Direct identification of flutter derivatives and aerodynamic admittances of bridge decks

Flutter derivatives and aerodynamic admittances provide basis of predicting the critical wind speed in flutter and buffeting analysis of long-span cable-supported bridges. In this paper, one popular stochastic system identification technique, covariance-driven stochastic subspace identification (SSI in short), is first presented for estimation of the flutter derivatives and aerodynamic admittances of bridge decks from their random responses in turbulent flow. Numerical simulations of an ideal thin plate are adopted to extract these aerodynamic parameters to evaluate the applicability of the present method. Then wind tunnel tests of a streamlined thin plate model and a Π type blunt bridge section model were conducted in turbulent flow and the flutter derivatives and aerodynamic admittances are determined by the SSI technique. The identified aerodynamic parameters are compared with the theoretical ones and the results indicate the applicability of the current method.

Determination of flutter derivatives by stochastic subspace identification technique

Flutter derivatives provide the basis of predicting the critical wind speed in flutter and buffeting analysis of long-span cable-supported bridges. In this paper, one popular stochastic system identification technique, covariance-driven Stochastic Subspace Identification(SSI in short), is firstly presented for estimation of the flutter derivatives of bridge decks from their random responses in turbulent flow. Secondly, wind tunnel tests of a streamlined thin plate model and a <TEX>${\Pi}$</TEX> type blunt bridge section model are conducted in turbulent flow and the flutter derivatives are determined by SSI. The flutter derivatives of the thin plate model identified by SSI are very comparable to those identified by the unifying least-square method and Theodorson's theoretical values. As to the <TEX>${\Pi}$</TEX> type section model, the effect of turbulence on aerodynamic damping seems to be somewhat notable, therefore perhaps the wind tunnel tests for flutter derivative estimation of those models with similar blunt sections should be conducted in turbulent flow.

Discussion: Measuring Flutter Derivatives for Bridge Sectional Models in Water Channel

Discussion: Measuring Flutter Derivatives for Bridge Sectional Models in Water Channel

Closure to “Measuring Flutter Derivatives for Bridge Sectional Models in Water Channel” by Q. C. Li

Closure to “Measuring Flutter Derivatives for Bridge Sectional Models in Water Channel” by Q. C. Li

Numerical approach for wind loads prediction on buildings and structures

An investigation of the ability of numerical codes to predict wind loads on buildings and structures, using k−ϵ closure model for turbulence, has been undertaken at CSTB. We present in this paper four cases for which wind-tunnel measurements are available: Pressure coefficients around a cube model and a house model in a simulated atmospheric boundary layer, drag and lift forces on a hoarding model and a bridge section model, located in the CSTB climatic wind tunnel.

Measuring Flutter Derivatives for Bridge Sectional Models in Water Channel

Experimental results of flutter derivatives for sectional models of long-span bridges are presented. The tests were carried out in the Water Channel Laboratory of the Center for Applied Stochastics Research of Florida Atlantic University, which has an 8-m-long test section and a maximum flow speed of 0.5 m/s. The experiments were conducted in the forced-oscillation mode. Specifically, each model is forced to execute a sinusoidal motion, either torsional or vertical, one at a time. In each test, both lift force and torsional moment are measured to obtain the noncoupled flutter derivatives as well as the coupled ones. The advantages of using water as the fluid medium, instead of air, are described. The flutter derivatives obtained in the water-channel tests are then compared with some published data obtained in the wind-tunnel tests using the free-vibration mode. The comparison shows that the water-channel data and the respective wind-tunnel data share the same trends. Finally, the measured flutter derivatives are converted to the corresponding impulse response functions required for the stochastic stability analysis in the time domain.

Mechanism of vortex-excited oscillations of a bridge deck

The results of a wind-tunnel study of vortex-induced response of a cable-stayed bridge deck are presented. A bridge section model was employed in smooth flow. The experiments included measurement of the model aerodynamic response and flow visualization. The results indicated existence of two mechanisms causing the vortex-induced model response. One is related to the Kármán voritces shed in the wake. The other mechanism is associated with occurrence of the motion-induced vortices.

Wind-tunnel study of effects of geometry modification on aerodynamics of a cable-stayed bridge deck

The results of a wind-tunnel study of the aerodynamic response and stability of a cable-stayed bridge deck are presented. A bridge section model was employed in smooth flow and the effects of modifying the bridge geometry were investigated. The results showed that the original bridge deck was unstable in torsion and exhibited high, vertex-induced, vertical oscillation. Streamlining of the deck resulted in improved aerodynamic performance, with an increase in the critical wind speed for torsional flutter and decrease in the vortex-induced response.

Wind-tunnel study of aerodynamic stability and response of a cable-stayed bridge deck

The results of a wind-tunnel study of the aerodynamic response and stability of a cable-stayed bridge deck are presented. A bridge section model was employed in smooth flow and the effects of relaxing the Froude number similarity and modifying the bridge geometry by the removal of traffic barriers were investigated. It was verified that the Froude number similarity can be relaxed. The results showed that the bridge deck was unstable in torsion. Removal of the traffic barriers resulted in improved bridge deck aerodynamic behavior, i.e. an increase in the critical wind speed for torsional flutter and a decrease in the vortex-induced response.