Issue 29

D. De Domenico et alii, Frattura ed Integrità Strutturale, 29 (2014) 209-221; DOI: 10.3221/IGF-ESIS.29.18 209 Focussed on: Computational Mechanics and Mechanics of Materials in Italy Limit analysis on FRP-strengthened RC members D. De Domenico, A.A. Pisano, P. Fuschi University Mediterranea of Reggio Calabria, Department PAU dario.dedomenico@unirc.it , aurora.pisano@unirc.it, paolo.fuschi@unirc.it Dedicated to Professor Castrenze Polizzotto on the occasion of his 90 th birthday A BSTRACT . Reinforced concrete (RC) members strengthened with externally bonded fiber-reinforced-polymer (FRP) plates are numerically investigated by a plasticity-based limit analysis approach. The key-concept of the present approach is to adopt proper constitutive models for concrete, steel reinforcement bars (re-bars) and FRP strengthening plates according to a multi-yield-criteria formulation. This allows the prediction of concrete crushing, steel bars yielding and FRP rupture that may occur at the ultimate limit state. To simulate such limit- state of the analysed elements, two iterative methods performing linear elastic analyses with adaptive elastic parameters and finite elements (FEs) description are employed. The peak loads and collapse mechanisms predicted for FRP-plated RC beams are validated by comparison with the corresponding experimental findings. K EYWORDS . Finite element modelling; Multi-yield-criteria limit analysis; Reinforced concrete elements; FRP- strengthening systems. I NTRODUCTION any existing steel-reinforced concrete structures, including decks and beams in highway bridges as well as beams, slabs and columns in buildings, are being assessed as having insufficient load carrying capacity due to their deterioration, ageing, poor initial design and/or construction, lack of maintenance, corrosion of steel reinforcement or underestimated design loads. In other cases they no longer comply with the current standards and requirements because of changed load conditions or modification of structural system for some reason. It is both economically and environmentally preferable to upgrade these structures rather than replace/rebuild them, even more if rapid, simple and effective strengthening techniques are employed. In this context, flexural and/or shear repair and rehabilitation of RC structures with externally bonded fiber reinforced polymer sheets, strips and fabrics is generally viewed as a valid and viable solution. Moreover, these techniques can be carried out while the structure is still in use as well as they can be targeted at where the structural deficiency is more marked [1, 2]. On the other hand, to estimate the actual efficacy of the strengthening system, without performing expensive laboratory tests, as well as to design the proper repair interventions to reach a given gain in load carrying capacity, analytical tools and predictive numerical models are highly needed. Experimental investigations confirm that, after the application of such FRP techniques [3], a significant increase in flexural/shear capacity of the RC elements (up to about 125%) is achieved. Experiments also show the enhancement of the confinement effect exerted on concrete by the FRP laminates, resulting in shifting the failure mode of the strengthened elements from brittle concrete crushing to more ductile steel yielding and/or FRP rupture [4]. In fact, the FRP strengthening system mitigates crack development and, as a result, increases the overall ductility of the RC element. The above considerations make indeed a limit analysis plasticity-based numerical approach, among many others presented in M