An existing reinforced concrete building with moment-resisting frames can be vulnerable during an earthquake owing to its deficient columns. The present paper reports a study on the enhancement of flexural strength and behaviour of columns, by concrete jacketing. First, the performance of the interface of additional concrete cast against the prepared surface of existing concrete was studied. Tests were then conducted on reference (without strengthening) and jacketed column specimens, to study the enhancement of strength of a retrofitted column section under the interaction of axial load and bending moment. Subsequently, interior beam–column–slab sub-assemblage specimens were tested under simultaneous vertical and lateral loading. It was observed that the selected jacketing scheme was effective in enhancing the flexural strength, as well as in retaining the ductility and energy dissipation in the behaviour. The moment–curvature behaviour of a retrofitted column section was predicted based on the layered analysis. The information was fed in the lateral load against drift analysis of a computational model of a retrofitted sub-assemblage specimen, using an incremental non-linear technique. The paper presents the method of analysis and guidelines for retrofitting of columns for seismic forces. © 2014, Thomas Telford Services Ltd. All rights reserved.