Influence of geometric parameters on residual stresses in cold formed structural steel details : a parametric study

The need and usage of cold-formed steel members increased rapidly after the technological advancements and developments in roll forming industry. Racking industry is one of the areas in which cold-formed steel is mostly used. Increasing storage demand and technological innovations led to the trend of storage Racking and Shelving (R&S) systems with multi-level cranes, where the cold-formed rack structure has to support the Storage and Retrieval (S/R) machines. With faster and heavier S/R machines working on a 24/7 basis, higher dynamic actions act on the rack. The estimated number of cycles can reach to 0.5 million/year. Consequently, the cyclic loads can no longer be considered negligible; racking systems and components must be designed for fatigue loading. In European design codes, fatigue design rules for cold-formed steel sections and details are not covered particularly. “EN 1993-1-3: General rules - Supplementary rules for cold-formed members and sheeting” concerns only with the static design of cold-formed thin-walled sections and fatigue is not mentioned. On the other hand, fatigue design is introduced in “EN 1993-1-9: Eurocode 3: Design of steel structures - Part 1-9: Fatigue” however it is not covering the design and classification of cold-formed thin-walled details. For the European logistic industry, the total lack of fatigue assessment rules for cold-formed steel members corresponds to a crucial problem causing losses estimated around 25-30 million €/year. This study is a part of FASTCOLD (FAtigue STrength of COLD-formed structural steel details) research project. FASTCOLD, with an estimated project duration of four years, aims at generating essential knowledge in the field of fatigue assessment of cold-formed steel structural details, as the results will be presented in a way compatible for immediate implementation in Eurocodes. For a comprehensive fatigue assessment, residual stresses in members should be well known. The aim of this study is to analyze and investigate the behavior of residual stresses occurred due to cold-forming in bent corners of cold-formed steel members.