Experimental and numerical investigations for the structural characterization of a historic RC arch bridge

A comprehensive rational methodology for the structural assessment of existing bridges is presented and specifically applied to a historic reinforced concrete arch bridge. The methodology is based on the use of non-destructive testing tools and structural model updating procedures and involves: (a) preliminary documented research and on-site geometric surveys (aimed at collecting information on the "as built" geometry); (b) ambient vibration testing performed by using a grid of conventional high-sensitivity accelerometers, aimed specifically at investigating the vertical dynamic characteristics of the bridge and c) development of an updated Finite Element (FE) model of the structure. The investigated bridge, completed in May 1917, crosses the Adda river between Brivio (province of Lecco) and Cisano Bergamasco (province of Bergamo), about 50 km North-East from Milano, Northern Italy. Given the still strategic position of the bridge in the current road transportation network and within a systematic surveillance program of main infrastructures by the Province of Lecco, dynamic tests were performed under operational conditions. Main results in terms of Operational Modal Analysis and FE modelling and updating are presented and discussed. A hierarchy of FE models with different levels of refinement is developed, with the purpose of a future selection of the model that better reproduces the current structural properties of the bridge. In this paper an automated system identification procedure has been developed and applied to the simplest of the assembled (consistent) FE models, whose results will constitute a benchmark for further studies upon the other most refined models. The aim is to perform a final baseline reference model to be used for reliability assessment within Structural Health Monitoring (SHM) purposes.