Load and Resistance Factor Design of Strip Footings

Abstract

This paper proposes a Load and Resistance Factor Design (LRFD) approach for the bearing capacity design of a strip footing. The load factors used are as specified by the National Building Code of Canada. The resistance factors required to achieve a certain acceptable failure probability are estimated as a function of the spatial variability of the soil as well as by the level of “understanding” of the soil properties in the vicinity of the foundation. The analytical results are validated by simulation. The results are primarily intended to aid the development of the next generation of reliability-based geotechnical design codes, but can also be used to guide current designs. Introduction Design of a shallow footing typically begins with a site investigation aimed at determining the strength of the founding soil or rock. Once this information has been gathered, the geotechnical engineer is in a position to determine the footing dimensions required to avoid entering various limit states. The limit states that are usually considered in the footing design are serviceability limit states (typically deformation) and ultimate limit states. The latter is concerned with safety and includes the load-carrying capacity, or bearing capacity, of the footing. This paper develops a load and resistance factor design (LRFD) approach for strip footings designed against bearing capacity failure. The design goal is to determine the footing dimensions such that the resistance to the load, Ru, satisfies