Simplified model for compressive response of RC column footing with square cross-section

Abstract

In this paper, a simplified calculus model for the prediction of the compressive response of RC column footing with a square cross-section is presented. As it is well-known RC concrete footing are designed adopting uniform contact pressures on the substrate and assuming a strut and tie model in deep members and a cantilever beam or slab model in flexible members. Deep and flexible members are distinguished in literature only based on the tangent of the angle expressed as the ratio between the depth and the shear span of the footing. In this paper, several subgrade contact pressures distribution for column footings (rigid or soft soils) were considered in developing a mechanical model able to derive the complete load displacement curves of RC deep and flexible footing in compression. The objective of the research was the more appropriate choice of the calculus model to predict the compressive response of single column footing. In particular, if the angle, expressed as the ratio between the depth and the shear span of the footing, is higher than 45 the strut and tie model was suggested for best prediction, while, if the angle is lower than 45, the beam or the slab models with punching shear were adopted. For both cases simplified loading soil profiles corresponding to rigid, flexible or winker model were adopted. Effects of main parameters such as geometry (depth, width) and shape of footing (single or shaped), the mechanical ratio of longitudinal reinforcement and type of soil are investigated both numerically and analytically. Numerical results and available experimental results were utilized to verify the model. The comparison between analytical and numerical results allows one to validate the proposed model and to define the range of application of the strut and tie or beam model depending on the footing geometry, the mechanical ratio of longitudinal reinforcement and type of soil. Finally, the comparison between analytical and experimental results available in the literature gives a further confirmation on the reliability of the proposed model.