Fiber Reinforced Polymer Confinement of Bridge Columns Suffering from Premature Bars’ Buckling – Strength empirical model

A critical review of the anti-buckling strengthening design procedures of the bars of existing reinforced concrete (RC) columns through fiber reinforced polymer (FRP) confinement is presented. Furthermore, the results of a parametric analytical study, performed by the authors, using finite element method for old-type existing columns with optional steel bars’ buckling under compression are utilized in order to propose an upgraded empirical strength model. The parametric study involved column models constructed with three-dimensional finite elements for concrete and steel incorporating plasticity theory and laminas for FRP jacket elastic response. After elaboration of the parametric finite element analyses of characteristic RC columns, the effect of the existing bars’

yield strength on the behaviour of FRP strengthened columns is evaluated covering all qualities of steel met in existing columns. Finally a strength model sensitive to bars’ quality is proposed for the design of RC columns confined by FRP jackets, that requires no estimation of the effective failure strain of the FRP jacket, as it was found strongly related to the axial rigidity of the confining FRP device and the strength enhancement of the concrete core. The model is compared against an extensive database of experimental results. The proposed model provides remarkably accurate strength prediction results for the abovementioned strengthening applications.