Fatigue behaviour of RC bridges with externally bonded CFRP reinforcement

Author: Povilas Ambrasas
Language: English

Abstract

Externally bonded carbon fibre reinforced polymers (EB-CFRP) have been used for structural applications for the last three decades. Structural retrofitting is the area where fibre reinforced polymer laminates are particularly widespread especially when used as an EB-reinforcement of concrete structures. The design of retrofitting measures with CFRP materials is highly standardised and its application may be regarded as state-of-the-art in this field. However, most of the technical codes provide very little (bending retrofit)/ no (shear retrofit) consistent design rules concerning EB-CFRP reinforcement used for structures experiencing fatigue loading, such as bridges. In this thesis, resistance to fatigue loading of reinforced concrete members strengthened with EB-CFRP reinforcement was investigated, both on material and structural level, with emphasis on fatigue degradation of the interface between concrete and CFRP reinforcement.
It was shown that for load ranges typical for bridges, the fatigue resistance of the internal steel reinforcement usually governs the resistance of reinforced concrete beams undergoing dynamic loading and strengthened with EB-CFRP in order to increase the bending resistance. If the structure is exposed to higher load levels, though, the integrity of the member may be decreased due to damage at the concrete-CFRP interface. Nevertheless, if the rules of existing design guidelines are followed, the loss of externally bonded reinforcement would not lead to complete collapse of the structure.
When shear strengthening with externally bonded CFRP is considered, no mechanically consistent approaches exist to determine the stress state of the bond between concrete and CFRP under service loads. To overcome this limitation, approaches for determining the behaviour of reinforced concrete members subjected to shear load may be extended to take into account the effect of EB-CFRP reinforcement. In this way, it is possible to determine the stress state, e.g. in the webs of reinforced concrete beams strengthened for shear with CFRP stirrups. The results may be used to determine the fatigue life of internal transverse steel reinforcement and to identify whether concrete-CFRP bond damage is expected during the lifespan of a strengthened structure.
The findings of present thesis contributes to better understanding of fatigue behaviour of reinforced concrete members strengthened with externally bonded CFRP reinforcement, an item hardly covered in most of the current design codes.