Slender structures are set into vibration transverse to the wind direction due to alternating vortex shedding when the frequency of vortex shedding matches the structure’s natural frequency. This phenomenon can be observed in the Steel Structures Department’s wind tunnel using sectional models in laminar flow. The video shows a circular cylindrical test specimen on which the onset velocity and transverse vibration amplitude were measured. The study was conducted as part of a master’s thesis based on the content of the module “Wind Engineering and Structural Dynamics.”

The reason for the experiments on vortex-induced transverse vibrations is the upcoming change in the calculation method. To date, DIN EN 1991-1-4 has provided for two methods for calculating the maximum transverse vibration amplitude. The national annex stipulates that only Method 1, also known as the effective length method, is to be used in Germany. However, the current draft of the Eurocode provides for only a revised form of the spectral method as the sole method for calculating the lateral vibration amplitude. The onset speeds and lateral vibration amplitudes measured in the wind tunnel test provide comparative values for assessing the suitability of the different calculation methods.

The video recording of the test shows the lateral vibration amplitude increasing as the wind speed rises. If the critical wind speed—which is 2.1 m/s for this test setup—is exceeded, the amplitude decreases again. Since the first and second natural frequencies of the test specimen are close together, the specimen begins to oscillate proportionally at the second natural frequency as the wind speed continues to increase.