Experimental Damping Identification of a Bridge Case Study in Norway under Still Air Conditions

Aeroelastic effects are a fascinating yet problematic phenomenon that lies in between the fields of aeronautical and bridge engineering, as many long-span bridge decks show dynamic behaviors similar to the ones of wing airfoils when met with strong winds. In particular, modal damping is a critical factor in understanding the dynamic behavior of bridges when exposed to these kinds of interactions between aerodynamic forces and their structural elastic properties. This short contribution presents an in-depth investigation of modal damping identification through output-only operational modal analysis (OMA) in a bridge deck case study in Norway subjected to still-air conditions, where aeroelastic damping can be neglected. However, in this long-span suspension bridge, its slenderness implies having several closely-spaced modes of interest below 1.00 Hz. Therefore, the herein-considered still air wind condition represented a critical situation for proper activation of some first modes of interest, highlighting that experimental OMA can not properly identify the right value of the expected structural damping ratio associated with those modes from comparisons with other literature results