Investigation of the interface behaviour of retrofitted concrete columns through finite elements

The current study deals with an analytical investigation of the behaviour of the interface of retrofitted concrete columns with RC jackets through FE analysis. Appropriate plasticity and constitutive models are used to simulate the behaviour of both concrete and steel bars. All analytical results are compared with the experimental ones that are subjected to axial repeated loads of cycles 5‰ of axial strains up to failure. Eighteen specimen of square section (section scale 1:2, 150x150x500mm) of approximate 20MPa nominal concrete strength are simulated and tested. Twelve of them contain 4 longitudinal bars of 500MPa nominal strength and normal confinement ratio (ωcc=0.15, closed stirrups of 220 MPa nominal strength). All columns were retrofitted with RC jackets with various confinement ratios (ωcj=0/0.035/0.071/0.142) and two different kind of interface reinforcement: dowel and bend- down bars. Two loading patterns are selected in order to examine the shear transfer mechanisms (Α) along the interface and the real loading conditions (B). The P-δ diagrams of specimens and dowels together with the flow stress diagrams along the interface path are presented. The result show that: a) the presence of welded bend down bars results in higher levels of initial stiffness, b) the FE analysis results are satisfying and close to the experimental tests since the deviation is under 10%, c) the path diagrams indicate the percentage of the stress concentrated at the region of the first dowel bar along with the amount of stress at each step of the analysis.