A truss model for the confinement of concrete columns

In order to investigate the dependence of the ductility of a concrete column on its confinement by transverse reinforcement, a part of a column, subjected to axial compression between two successive confined sections, is simulated by a plane truss, with bars obeying non-linear sigma-epsilon laws of concrete or steel The equilibrium conditions are written with respect to the deformed structure, so that instability phenomena are taken into account. The proposed model is applied on a column with square section first unconfined and then with increasing confinement, for various values of spacing of transverse reinforcement. Finally, a method of preliminary design, based on the truss model, is proposed for the preestimation of minimum required section of transverse reinforcement assuring ductility.