Advanced statistical analysis of vortex-induced vibrations in suspension bridge hangers with and without Stockbridge dampers

Abstract

This paper presents a detailed statistical analysis of strong hanger vortex-induced vibrations (VIV) at the Hålogaland Bridge in Narvik, Norway. Severe VIV during construction led to the installation of Stockbridge dampers post-completion. Unfortunately, many dampers broke within a year, prompting a long-term measurement campaign. The measurements highlight the complexity of observed VIV, with non-stationary and multi-frequency vibrations during constant wind speeds. The paper assesses the effectiveness of various damper configurations on the hangers and finds that a single damper notably reduces vibration amplitudes, however, installing more dampers results in a lower observed difference. The research includes a detailed statistical analysis of wind data and cable responses, considering different observation intervals since the observed time of development of lock-in vibrations might impact the VIV statistical indicators. It is also shown that the duration over which wind can be considered stationary most often differs from the conventional 10-minute duration. Finally, using statistical hypothesis testing, it is demonstrated that VIV metrics are slightly influenced by the observation interval length, and it is confirmed that high turbulence intensity significantly limits the amplitude reached at synchronization. Overall, this research provides valuable insights into understanding and addressing challenges related to measuring and interpreting vortex-induced vibrations on hangers.