A monitoring system for determination of real deck slab behaviour in prestressed box girder bridges

Due to ever increasing traffic demands the fatigue safety and service life of the bridges of a railway line in Brazil need to be examined. Conventional assessment methods using load models and approaches as suggested in codes lead to conservative results resulting in significant strengthening interventions. Due to the important direct and indirect costs of the intervention, more detailed examination methods based on data as obtained from monitoring is suggested. This paper reports on an ongoing study to examine the fatigue safety of one standard bridge type, i.e. riveted steel truss structure. First resultsDeck slabs of road bridges are particularly exposed to high numbers of fatigue inducing stresses. It can be difficult to accurately model their service behaviour as secondary elements such as parapets, kerbs and surfacing layers reduce the stress levels in the steel reinforcement bars. Changes in material properties over time and thermal variations further complicate the process. For these reasons a monitoring regime is favoured for the accurate determination of real ‘action effects’ within the bridge elements. This paper presents a 1960’s prestressed concrete motorway bridge in Switzerland which is instrumented with a remotely accessible structural health monitoring (SHM) system. The key focus of the study is on the direct measurement of strains in reinforcement bars to provide a better understanding of the real structural behaviour of such bridges. The system is used to show the signature of an extreme vehicle crossing event as strain and vibrational response in the structural elements. show that all bridge members are safe under the various limit states. The level of stress ranges found in the truss members due to fatigue loading are low such that only two members experience fatigue damage. The bridge structure has thus significant reserves in capacity which makes a future increase in axle loads feasible.