Efficiency of stress-strain models of confined concrete with and without steel jacketing to reproduce experimental results

The improvement and the capacity assessment of existing buildings has become the main topic of the last years so that different studies can be found devoted to damaged structures or structures not having a capacity compatible with the safety levels of the actual codes. Reinforced concrete framed structure buildings represent a conspicuous rate of the existing constructions so many efforts are addressed to them. Referring to this type of buildings, a good prediction of strength and deformation capacity requests models able to interpret the constitutive law of concrete confined by internal reinforcement or by eventual external reinforcement applied to increase capacity of cross-sections. Considering that one of the techniques much diffused for the improvement of the capacity of reinforced concrete members is the steel jacketing by the combined system of angles and battens, models able to predict the real contribution of this kind of intervention are desirable. In this connection the paper discusses the different confined concrete models available in the literature, analyzing all the characteristics and comparing the σ-ε constitutive laws for different type of RC cross sections. Also, an experimental campaign aimed to the validation of the above models is presented. Through the paper, the results of tests on columns reinforced with steel jacketing are described and the reliability of some costitutive laws for concrete confined by steel jacketing is examined.