A FE-BASED LIMIT ANALYSIS APPROACH FOR CONCRETE ELEMENTS REINFORCED WITH FRP BARS

The use of FRP reinforcements in concrete structures has increased rapidly in the last decade being a valid alternative to steel reinforcements. To guarantee a reliable design is essential to possess, as for the traditional reinforced concrete structures, codes able to catch the behaviour of such structures even above the elastic limit. Post elastic step-by-step analyses are the common tools available to this aim. A valid alternative for design purposes can be given by the so called direct methods, that are able to predict the load bearing capacity of a structure in terms of its peak load value. In the present study a numerical FE-based approach, known as Linear Matching Method (LMM) is used to tackle the addressed structural elements. A plasticity model for concrete is adopted in a three-dimensional framework with a pressure-sensitive yield surface and a non associated flow rule. The yield surface turns into the failure surface proposed by Menétrey and Willam. A cap in compression is adopted, while the FRP re-bars are treated as elastic-brittle elements working only in the fibres direction. The non associated flow, essential to take into account the volumetric expansion under compression exhibited by concrete, implies the lack of a unique peak/collapse load multiplier, the LMM is then applied to compute an upper bound to the peak load multiplier. Few examples are finally presented and critically discussed.