DESIGN EQUATIONS FOR EVALUATION OF STRENGTH AND DEFORMATION CAPACITY FOR UNSTRENGTHENED AND FRP STRENGTHENED RC RECTANGULAR COLUMNS UNDER COMBINED BIAXIAL BENDING AND AXIAL LOAD

摘要

When assessing the seismic performance of existing reinforced concrete buildings designed according to obsolete codes, one can identify potentially dangerous situations that could result in catastrophic failures. A typical inadequacy lies in the so-called "strong beam-weak column" situation: columns are no so strength to force plastic hinge formation in beams and, if this is extended to all columns at a given floor, can lead to the development of a soft-storey mechanism. Such weaknesses should be eliminated by upgrading all weak columns in the zones of potential formation of plastic hinges so to increase their flexural capacity and to force plastic hinge formation in the beams. With this aim one or more layers of FRP could be wrapped longitudinally along the column at the end zones. Nevertheless, the flexural strengthening can reduce the elements deformation capacity. This paper, starting from previous authors works propose a simplified procedure for the assessment of flexural strength and deformation capacity of rc unstrengthened and FRP strengthened reinforced concrete rectangular columns. Approximate closed form equations are developed by which the flexural strength and section ultimate curvature are evaluated as a function of the normalized acting axial load and the geometrical and mechanical sections parameter. The proposed approach is compared with a fibre approach.