Load Factors for Permanent Actions and Cable Preload in Cable-stayed Bridges

Abstract

Cable-stayed bridges are often the most economical solution for spans in the range of 150 to 500 m today and have therefore found widespread application over the past decades. In the design of cable-stayed bridges, the choice of partial factors applied on the permanent loads and the cable preload has a significant effect on economy and may even affect the feasibility of a project. While different design approaches are being used today, most designers consider the uncertainties of the two actions as correlated and hence apply the same partial factor to both actions simultaneously. However, in the frame of the development of the second generation of Eurocodes currently under way, a new code clause has recently been proposed which suggests considering different partial factors. The present paper aims to provide a basis for discussion based on the findings of a case study on three existing cable-stay bridges, where the impact of the aforementioned design approaches regarding the load factors for permanent load and cable preload was investigated. Based on the findings, recommendations for the load factors are given taking into account aspects of economy and safety.