Reliability analysis of EN 1997 design approaches for eccentrically loaded footings

Abstract

EN 1997-1:2004 provides a choice of three design approaches with various combinations of partial factors applied to loads, material properties and/or resistances. A modification to design approach 2 has been suggested in which actions are combined prior to being factored. The merits of this alternative, generally referred to as DA2*, are considered in the context of spread footings subject to vertical and horizontal loads (H and V), giving rise to inclined, eccentric loading at founding level. Evaluation of the reliability of strip and square footings designed according to design approaches DA1 to DA3, as well as DA2*, indicate that at high H/V the DA2* approach yields significantly lower reliability than the three recognised EN 1997-1:2004 options. In addition, the reliability of DA2* designs show a greater decrease with increasing H/V, as the approach does not meaningfully distinguish between favourable as opposed to unfavourable effects of vertical loads. It is shown that the approach effectively reduces the limit states design framework to a working stress design one. The approach is therefore considered to be less suitable for limit states design of eccentrically loaded shallow footings than the recognised options.