Buckling of Rectangular Isolated R.C. Columns: Closed-form Approximation for Interaction Domains

Interaction domains for the buckling of isolated R.C. columns are an efficient and versatile instrument for the assessment of the resistance at Ultimate Limit State, and allow the optimization of the structural geometry and reinforcement ratio. The paper presents the procedure for deriving interaction domains for rectangular symmetrically reinforced columns, providing a detailed analysis of the load-carrying capacity for various classes of concrete and reinforcement steel bars. Domains have been obtained according to the “model-column method”, taking into account the uncertainties both in geometry and in the position of axial loads. Effects related to short-term creep are ignored. In order to facilitate the practical utilization, the generic domain has been approximated by a two-branch curve, parabolic and elliptic. The first-one is related to the collapse dominated by axial load, and the second one to flexural crisis. This approximation leads to simple closed-form expressions, particularly suitable for engineering preliminary design.