CFRP strengthening of concrete slabs, with and without openings experiment, analysis, design and field application

Abstract: Rehabilitation and strengthening of concrete structures with externally bonded FRP (Fibre Reinforced Polymers) has been a viable technique for at least a decade. The most common way to strengthen a structure is in flexure where thedesign normally follows traditional concrete design, with exceptions for control of bond and anchorage related to the FRP. The method is also used for strengthening in shear and torsion, as well as for strengthening of columns. An interesting and useful application is strengthening of slabs or walls without or with openings. In the latter situation, FRP sheets or plates are very suitable; not only because of their strength, but also due to the simplicity in theexecution in comparison to traditional steel girders or other lintel systems. Even though many benefits have been shown in the use of FRP strengthening of openings in practical applications, not much research have been presented in the scientific literature. In this licentiate thesis, the results from laboratory tests on strengthened slabs loaded with a uniformly distributed load are analyzed with analytical and numerical methods. The slabs with openings have been strengthened with CFRP (Carbon Fibre Reinforced Polymers) sheets and are compared to traditionally steel reinforced slabs, both with and without openings. The results from the tests show that slabs with openings can be strengthened with externally bonded CFRP sheets. The performance is, in comparison, even better than for traditionally steel reinforced slabs if bond failure can be avoided. The numerical and analytical evaluations are in good agreement with the experimental results. The case study presented in chapter 5, shows a practical design application of a courtyard deck strengthened with CFRP using epoxy bonded plates. It also points out the difficulties in retrofitting of existing structures. Since the information was inadequate when the original design was performed, an active design approach was used i.e. the design was changed when the true site conditions was revealed during the reconstruction work.