Niloufar Vahedi
Bridges are a critical component of national infrastructures and economies. A significant percentage of bridges built all around the world are made of reinforced concrete which according to building codes have a life span between 80-100 years. However, structural inspections demonstrate that deterioration can begin in as little as 10 years due to the limited durability of steel-reinforced concrete. Exposure to humidity, freeze-thaw cycles and de-icing salts during winter result in corrosion of the steel reinforcement and spalling of the surface concrete which subsequently lead to partial or full bridge closure for required repair. Maintenance, upgrading and replacement of bridges may have significant economic and social impact due to disturbances in traffic flow. Mentioned reasons motivated scientists and engineers to develop and use more durable alternative materials with lower life-cycle cost. Composite sandwich bridge decks composed of glass fiber-reinforced (GFRP) face sheets and a balsa wood core, which are subject of this projects, provide the possibility of a more durable, lightweight and easily installed alternative. Balsa wood is a lightweight wood species exhibiting high strength- and stiffness-to-weight ratios, and therefore it is a favorable core material in bridge decks. However, this new type of sandwich bridge decks has to meet the same requirements as traditional concrete decks do. In particular, their behavior during a fire incident has to be known and predictable. Although fire is an accidental action according to Eurocodes, it has to be taken into account in the design of bridges and should not lead to a premature collapse. The knowledge about the combined thermo-mechanical behavior during a fire of these new sandwich decks is therefore crucial, in particular since the polymer matrix of the GFRP material and the balsa core are sensitive to high temperatures and combustible.GFRP sandwich structures are also used in other high-risk fire applications, e.g. in the automotive, naval and aerospace fields and numerous works about their thermo-mechanical behavior have been performed. However, these results cannot be simply transferred to GFRP-balsa sandwich bridge decks which are subjected to much more severe loads and their life span is much longer. The aim of this project is thus to investigate the thermo-mechanical behavior of GFRP-Balsa sandwich bridge decks in order to overcome this barrier of insufficient knowledge.Three level of investigations are planned, a) on the constituent material level, b) on the sandwich panel level, and c) on the bridge deck and superstructure level. Experimental investigations and modeling are conducted on each level from small- to full-scale. Since the performance of GFRP laminates under elevated temperatures have been investigated by many researchers, only thermo-physical and thermo-mechanical properties of balsa wood are investigated by proper experiments. At the second level, thermo-mechanical sandwich response models are developed and validated by experiments. The final level is conducted in order to investigate the thermo-mechanical behavior of the bridge deck at the structural system level which includes adhesively-bonded joints between the individual balsa panels of the deck and between the deck and the bridge girders. Furthermore, post-fire recovery models are established in order to assess the remaining structural capacity after a fire incident.
EPFL2022
