INFLUENCE OF RESIDUAL STRESSES ON THE FATIGUE LIFE OF COLD FORMED PROFILES USED IN AUTOMATED WAREHOUSES

Cold-formed steel members are increasingly adopted in racking systems installed in logistic warehouses where "storage and retrieval" (S/R) machines run faster and faster, while carrying heavier and heavier loads in a "7 days - 24 hours" economy. For this reason, loading conditions on these types of racks and their auxiliary structures are not anymore quasi-static but dynamic, and cold-formed steel structural details may be subjected to load cycles in the order of 0.5 million/year. Fatigue design rules for cold-formed steel sections and details are completely missing on a European level. EN 1993-1-3, deals only with the static design of cold-formed thin-walled sections. This total lack of fatigue assessment rules for cold-formed steel structural details at European level represents a relevant problem for the whole European logistic industry, causing losses estimated in the order of 25-30 millions/year. The presence of residual stresses and surface texture induced by the cold rolling (or press breaking) process affects the fatigue behaviour of cold-formed steel details. This paper, developed within the numerical activities of the EU-RFCS project FASTCOLD, aims at introducing the problem of fatigue for cold formed steel sections, analysing the residual stresses and their effect on the field of fatigue of cold-formed steel structural details.