Amplified moments in reinforced concrete core-walls

A finite element formulation for the out-of-plane buckling analysis of reinforced concrete walls is presented. The formulation is based on an orthotropic constitutive model for concrete. An in-plane analysis is firstly carried out to determine the stresses and tangent moduli. Out-of-plane, the concrete is modelled using non-linear orthotropic 16 DOF plate bending elements; the reinforcing steel using elasto-plastic fibre-type elements. In the plane of the structure stresses are calculated using either 4 or 8 node membrane elements with bar elements used for the reinforcing steel. Examples are presented for different boundary conditions and for walls with out-of-plane imperfections. The magnitude and distribution of amplified moments due to second order effects are discussed.