Performance of a historical cantilever reinforced concrete bridge with half-joint degradation

Abstract

The lack of maintenance of roadway concrete bridges built from the Second World War until the 70 s of the 20th century has led in recent years to an ever-increasing request for safety assessments. When bridge performance in terms of Serviceability Limit State (SLS) and Ultimate Limit State (ULS) has to be evaluated, in-situ visual inspections and load tests for safety and maintenance assessment have to be coupled with structural analysis. In order to identify a sound bridge structural model and to assess the actual conservation state, more refined models than those usually considered for section and reinforcement design should be used to reproduce the results of load tests and perform global and local safety checks in the structural elements. These needs are exemplified here through an assessment of the performance at SLS and ULS of a three-span cantilever reinforced bridge designed by Riccardo Morandi in Southern Italy. The central beam between the cantilevers is prestressed with bonded tendons while the side spans are made of ordinary reinforced concrete. Critical aspects of the bridge behaviour together with deficiencies due to deterioration and lack of maintenance over time, in service life, are investigated. The results of a structural assessment performed with Finite Element models are presented, through a comparison between different approaches and grades of structural analysis and through validation with in-situ investigations. Safety assessment of the half-joint is focused comparing the results obtained from strut-and-tie models supplied by Eurocodes and specifically developed for the case-study, considering the actual arrangement of the Gerber saddle. The results of this study show that a safety assessment of half-joints based on the literature and code models can lead to unreliable evaluations and that only global and local FE models validated through in-situ investigations allow the engineer to perform a reliable evaluation of safety in existing bridges.