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Aerodynamic stability and buffeting response due to turbulent wind have a fundamental importance for long-span bridge design. However, there are no benchmark cases that can be used as a reference estimate for an independent validation of the numerical methods and theoretical approximations. Therefore, the IABSE Task Group 3.1 proposal is to fill this gap by defining a reasonably well predicted set case for the response to wind of long-span bridges, both in terms of aerodynamic stability and buffeting. Specifically, a statistical analysis was performed on the numerical results collected by the task group participants, who used their own methodology and tools (either in time domain and/or frequency domain) to predict the bridge stability to flutter and buffeting response to wind, sharing the same input data (wind conditions, bridge structural properties, and deck aerodynamic coefficients). The benchmark results presented in this paper can be used as a point of reference for other numerical codes, and they include the onset of flutter speed, damping ratio variation with mean wind speed and the root mean square of the displacements as a function of mean wind speed, power spectral density values, and time histories of displacements. [ABSTRACT FROM AUTHOR]

From an aerodynamic point of view, very large observation wheels are complex structures. Several parts are slender with bluff cross sections, and therefore wind–structure interaction effects can influence their dynamic behaviour. Vortex-induced vibrations (VIVs), wake-effects, galloping instability, wind–rain interactions and buffeting response must be considered and studied during the design of substructures such as the A-frames and spoke cables. Both wind-tunnel tests and numerical tools can be used to assess the expected vibration levels and eventually to design appropriate countermeasures. In this paper, the Ain Dubai observation wheel is taken as a test case to present a procedure that can be applied to verify and validate the design of such structures when considering the effects of natural wind. For the A-frame, which turned out to be prone to VIVs during wind-tunnel tests on a scaled model, tuned mass dampers are studied as mitigation devices; for the spoke cables, several parameters affecting their aerodynamics were investigated in a wind tunnel on a full-scale model: inclination angle, structural damping and LED equipment. The characterization of these effects allowed both the performance of the cable damping system to be assessed, and configurations that could not perform adequately to be discarded. [ABSTRACT FROM AUTHOR]

IABSE Task Group 3.1 has the mandate to define reference results for the validation of methodologies and programs used to study both stability and buffeting responses of long-span bridges. To this end, the working group set up a benchmark procedure consisting of several steps with increasing complexity to define reference results useful for this validation. The simplest step (1.1a) was presented in Part 1. In this paper (Part 2), the contributions and reference results of the second sub-step (1.1c) are discussed. It consists of the simulation of the aeroelastic response of a three-degree-of-freedom bridge deck section forced by turbulent wind, using experimental aerodynamic coefficients measured in a wind tunnel. The increase in complexity, compared to the previous step, involves the experimental definition of unsteady force coefficients that are defined in a limited range of reduced velocities, and inclusion of the lateral motion and horizontal turbulent wind velocity components. Comparison of the different outputs, obtained by Task Group 3.1 participants with the same input data, is presented, revealing differences that are not always negligible. Moreover, the increase in complexity of the test case results in larger spreads of the results compared to the fully analytical case, analysed in Part 1. [ABSTRACT FROM AUTHOR]

IABSE Task Group 3.1 has the mandate to define reference results for the validation of methodologies and programs used to study both stability and buffeting responses of long-span bridges. These tools for the simulation of the aeroelastic behaviour are fundamental in the safe design of bridges and they should be validated. The working group decided to set up a benchmark procedure consisting of several steps to define reference results for this validation. For each step, contributors use their own methodology to simulate the bridge behaviour using the same input data. All the results are then compared, and reference values are defined through statistical analysis. The benchmark procedure is considered as a three-step problem with substeps of increasing difficulty: Step 1 compares numerical results only, Step 2 is validation against wind tunnel experiments, and Step 3 is validation against full-scale data. In this paper, the contributions and the reference results of the simplest initial substep (1.1a) are presented. It consists of the simulation of the aeroelastic response of a two-degree-of-freedom bridge deck section, with analytical aerodynamic coefficients, forced by turbulent wind. Despite the problem's simplicity, differences in some contributions are significant, confirming the necessity of having solid references to validate software programs. [ABSTRACT FROM AUTHOR]