Output-only modal identification of Luiz I Bridge before and after rehabilitation

Abstract

Luiz I Bridge is a double deck metallic arch bridge over Douro river at the city of Porto, in Portugal, built in 1885 by Eiffel's former engineer Theophile Seyrig. Recently, the local authorities decided to use the upper deck of this bridge to install a line of the new light metro of Porto, which required the development of significant rehabilitation works, involving the modification of the upper deck and the replacement and strengthening of a significant number of structural components, due to the important level of deterioration observed. This paper describes the experimental work developed before and after rehabilitation, aiming the accurate modal identification of the bridge at two different stages. The data collected in the second test was analysed using three different output-only modal identification techniques: Peak-Picking, PolyMax and covariance driven Stochastic Subspace Identification (SSI-COV).