A simple expression to evaluate bending capacity and compression zone height of rectangular RC wall sections

Seismic design codes require verification of sufficient bending capacity of reinforced concrete (RC) wall structures. It is often thought that a very conservative approximation of the capacity is acceptable. Yet, to comply with capacity design requirements, and considering also the shear demands, bending capacity should be known within a reasonable tolerance. Additionally, it is also important to evaluate the height of the compression zone in a given cross-section because it sets the design of the boundary elements and the confinement. To evaluate these two parameters accurately, engineers may use advanced softwares. However, this requires parametrization and calibration of the models, which may be too cumbersome, even for very detailed design cases. Thus, simplified and robust tools for the assessment of the wall bending capacity are required. This paper presents a simplified approach for the estimation of the moment capacity and the compression zone height of rectangular shear walls with distributed reinforcement, which are flexure-controlled. For that purpose, a fiber model has been programmed, verified and calibrated against published experimental results. Next, characteristic independent parameters have been chosen and brought to their non-dimensional form and each of them has been assigned with a practical range of values. A parametric study, based on 235 various cases, was performed by the previously calibrated fiber model. Based on the results of the parametric study, simple formulae for the bending capacity and the compression zone height are proposed. The parameters of these formulae are optimally evaluated, by minimizing the sum of square errors between them and the fiber model predictions.