Bonded FRP/steel deck-to-girder connections

Renovation of movable bridges

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Many movable bridges, built in the 1950’s and 1960’s, reach their end of service life or do not meet future traffic demands. Renovation of those bridge, if possible, is preferred over newly built from an economical point of view. Fibre-reinforced polymer (FRP) decks prove to be excellent for retrofitting bridge decks compared to traditional decks, mainly due to its high strength-to-weight ratio. Lightweight bridge decks are advantageous in movable bridges considering the savings on foundation, counter- weights and mechanical equipment, not to mention, reduced transportation costs, installation time and traffic hindrance during execution.
Connecting FRP decks to the steel girders can either be done mechanically (bolts), chemically (bonded) or in a hybrid fashion. Adhesively bonded connections do not require drilling in the FRP deck, thereby increasing its durability, have a more uniform stress distribution and fabrication costs are lower compared to bolted connections. Complex stress states and strength prediction of a bonded joints are yet not fully understood, therefore rarely being applied in primary load bearing structures like bridges.
This thesis focuses on the stress analysis and strength prediction of adhesively bonded connection between FRP decks and steel girders. An existing bridge, representative for renovation projects, is considered as case study. Its former bridge deck is replaced by a FRP deck and adhesively bonded to the steel girders. Structural analysis of the bridge deck performed with a global and local numerical model, focuses on the stress states in the bonded deck-to-girder connections. Traffic and thermal loads are the governing load cases, which show the largest stress concentrations. Peak stress levels are obtained along the edges and ends of the bonded connection between the FRP deck and secondary girders.
Comparison of results from the global and local model showed significant difference in stress levels and was further investigated. Stress concentration factors are determined to relate the (peak) stresses from the global and local model for different adhesive thickness and elastic modulus. Stress results from the global model are tweaked with the stress concentration factors and compared with strength values from literature. It can be concluded that bonded FRP/steel deck-to-girder connections are critical details in movable bridges.