Modal Testing of the Vasco da Gama Bridge, Portugal

Abstract

The Vasco da Gama Bridge is a 17-km crossing over the river Tagus in Lisbon that was constructed and opened to traffic on the occasion of the World Exhibition Expo'98. As part of the dynamic tests required at the commissioning stage, ambient and free vibration tests were developed on the five viaducts and on the main cable-stayed part that form the bridge, with the purpose of assessing the most relevant dynamic parameters in order to validate design studies and verify the safety condition of the structure. Focusing on the main cable-stayed bridge, the efficient strategy followed in order to form an extensive and high-quality database and the different techniques successively employed to identify modal properties are described, showing the potential of operational modal analysis in the assessment of the dynamic behavior of a complex structure and the usefulness of free vibration tests in the accurate identification of modal damping ratios. The full characterization of the dynamic behavior of the bridge provides the definition of the so-called zero-state condition of the bridge and has been used as reference in the subsequent surveillance and monitoring of the bridge that has been implemented by Lusoponte, the consortium that owns the concession of the bridge.