Determination of bearing capacity factors of ring footings using the method of stress characteristics

In this paper, the bearing capacity of ring footing is investigated. Ring footings are more economical in comparison with circular footings since less material is used in their construction. However, less investigation regarding the behavior and the bearing capacity of ring footings exits in the literature. The method of characteristics is applied in the present research in order to find the bearing capacity factors, which have been introduced in the so-called Terzaghi’s bearing capacity equation. The ring footing is assumed to be located on the horizontal ground surface, which carries vertical and centric load. The roughness between the footing base and the ground is ignored. The soil is assumed frictional-cohesive, which obeys Mohr-Coulomb yield criterion. The values of the bearing capacity factors are obtained for a wide range of soil friction angle (0~50 deg) and for different ring geometries in terms of the ratio of internal to outer ring radii (n), where n = 0, 0.2, 05, 0.7, and 0.9. The variations of the factors with n are presented in the forms of tables, graphs, and mathematical equations. The magnitude of the obtained factors is compared with the available data published in the literature. Comparisons show that there is good agreement between the results. In the end, by using some optional examples, it is shown that using the proposed bearing capacity equation for a ring footing is safe and conservative in comparison to applying a direct and rigorous plastic analysis.