Ultimate Limit State Design of Spread Foundations in The Case of Uplift

As vast majority of spread foundations are never subjected to vertical uplift loads, the subject of uplift capacity in such cases is barely covered by current European standards. Although the limit state design due to uplift is a subject of a section 10 of Eurocode 7, it mainly covers the possibility of a hydraulic failure while taking into the account any destabilizing variable actions. However, in the case of separate foundations of lattice towers used as support structures for overhead power lines, the uplift capacity of spread foundations often governs the design. The rules for the design of these structures are included in the informative annex M of EN 50341-1: 2012 Overhead electrical lines exceeding AC 1 kV – Part 1: General requirements – Common specifications. Rules presented in this standard differ significantly from those presented in Eurocode 7. The purpose of this paper is to present the design approaches for the limit state design of spread foundations subjected to uplift, while the differences between design rules and resulting variation of reliability are the primary concerns.