Steel jacketing of RC columns: Reliability of capacity laws for concrete.

In the seismic assessment of framed R.C. structures reinforced by steel angles and battens (steel jacketing) the use of proper confinement models for concrete is still a main topic. Really, the capacity of reinforced concrete columns under concentric and eccentric loads strongly depends on confinement exerted by the external reinforcement. Further a proper attribution of concrete stress-strain laws allows obtaining reliable estimations of inelastic capacity of reinforced elements. Moreover the presence (or not) of connections of the angles with the end joints influences their capacity to support vertical loads. In the two cases the mechanical models have to account for buckling or frictional effects. In this frame this paper presents a selected review of literature confinement models for steel jacketed concrete elements, presenting a parametric study in which the main confinement parameters predictable by each of them are compared. The reliability of the models in object is finally tested comparing analytical predictions of the ultimate vertical capacity with experimental results coming from several literature compressive tests of reinforced column specimens