Numerical analysis of concrete beams strengthened with CFRP: a study of anchorage lengths

The advantages of Fibre Reinforced Polymer (FRP) strengthening have been shown time and again during the last decade. All over the world several thousand structures have been retrofitted using FRP. Buildings and civil structures usually have a very long life and it is not uncommon that the demands on the structure change with time. The structures may have to carry larger loads at a later date or fulfil new standards. In extreme cases, a structure may need repair due to an accident, or due to errors made during the design or construction phase. To guarantee the function of the strengthening properties, anchorage of the FRP is essential. Without sufficient anchorage lengths, full utilization of the strengthening material cannot be achieved, leading to possible premature failure. In this paper, experimental work and numerical analyses of three different Carbon Fibre Reinforced Polymer (CFRP) strengthening techniques have been carried out. The techniques are externally bonded plates, sheets and the use of Near Surface Mounted Reinforcement (NSMR). The aim is to find a critical anchorage length, where a longer anchorage length does not contribute to the load bearing capacity. Three different anchorage lengths have been investigated; 100, 200 and 500 mm. The finite element program ABAQUS has been used for the numerical study. The results show that a critical anchorage length exists for plates and sheets as well as for NSMR. However, the present study also shows that an exact critical anchorage length may be difficult to estimate, at least with the present test set-up. Further tests and investigations of the constitutive model for the concrete are needed.