Numerical modelling of out-of-plane buckling of reinforced concrete walls under monotonic loading

Current design standards do not rigorously address the design of walls under monotonic loading subjected to the combined effects of axial load and in-plane moment, particularly in relation to buckling failure. Buckling occurs when compressive forces induce out-of-plane displacements, resulting in additional forces due to second-order effects. Although certain standards propose methods to account for this phenomenon, they tend to be based on overly conservative assumptions, which can lead to inefficient designs. The objective of this paper is to develop a more accurate design method for walls under combined axial load and in-plane moment. To achieve this, nonlinear finite element analysis (NLFEA) is performed to study the behaviour of walls under these loading conditions. Based on the findings from these analyses, an improved design method is proposed. This method introduces the concept of an equivalent column, for the compression zone of the wall. The compressive force in the equivalent column is derived from the internal equilibrium of the section. In addition, three key parameters relating to the effective stiffness in plate buckling are identified and introduced to refine the design procedure. By applying these factors, the proposed method provides a more realistic approach to wall design under combined actions, offering enhanced safety while reducing unnecessary conservatism compared to existing design standards.