Studio dell'intervento di rinforzo di un sovrappasso autostradale in struttura mista = Study of the reinforcement intervention of a highway overpass in a mixed structure

This thesis discusses and responds to the structural issues and reinforcement requirements of the SR.15 highway overpass, a mixed steel-concrete bridge located over the A4 Torino-Trieste Highway in Italy.The bridge was constructed between 2000 and 2003 and is 108 m long with a trapezoidal steel box girder and a reinforced concrete deck slab. The current setup is substandard for the current load demand, and it lacks adequate load-carrying members, construction distortions, support constraints, joint degradation, and corrosion. The first part of this discussion describes the bridge and its construction materials and parts including the box girder, concrete deck and support piers. The construction of the bridge uses both steel for it to be flexible and concrete for strength and load bearing but some of the features do not meet today’s standard. Assessments showed that there are essential regions in which structural members are not well positioned to bear higher loads and this causes stress concentrations, joint spalling and material failure. Additional changes to load bearing involve construction deviations such as welded hinges that were supposed to allow for rotation, aged support systems and degraded joint connections make the structure more vulnerable. The load combinations of permanent and variable loads such as traffic load, thermal loads and wind loads were calculated according to the modern design codes to check the structures for ULS and SLS. In this study, MIDAS Civil software was used to model the bridge behavior under these loads using finite element modeling (FEM) and generate 3D and 2D models of the structure that incorporated concrete creep, cracking, and long-term wear. The models proved that the bridge does not conform to the present load configuration requirements and established the effects of construction modifications and material degradation on the bridge. To fill these gaps, a specific reinforcement solution was suggested. The approach involves new lateral support elements added into the bridge framework in order to share load. In particular, new HEA 140 beams are arranged in the direction of the bridge width and are connected to the transverse structures with C-profiles. This reinforcement configuration increases the lateral stability, also the stress on the central structural parts, and the areas with high stress concentration are also improved to increase the load bearing capacity of the bridge. This thesis shows how structural documentation, accurate modeling, and phased intervention are vital in reinforcing a bridge. This paper provides practical implications for extending the service life of the SR.15 overpass to match modern load standards and retrofitting similar mixed-structure bridges, including recommendations for infrastructure maintenance, design compliance, documentation, and load assessment and intervention planning.