FAtigue STrength of COLD-formed structural steel details
FASTCOLD is a 42-month long research project funded by Research Fund for Coal and Steel (RFCS) of the European Commission.
The project started on July 2017 and has a total budget of 2.873.935 € and an EC financial contribution 1.724.361 €.
Steel profiles are either produced in steel mills starting from the melted substance: “hot rolled”, or from the semi-finished product (coiled) steel sheet to produce “cold-rolled” profiles (Figure 1). Substantial volumes of cold-formed steel are applied as corrugated sheet, as wall and roof purlins, as structural components in storage rack structures (Figure 2).
Especially in case of storage structures for the logistic industry, cyclic and dynamic loading produced by automatic storage and retrieval systems, such as shuttles (Figure 3) or stacker cranes supported by the rack structure, is introducing steel fatigue into the design.
Figure 1
Cold-rolling of a steel profile
Figure 2
Example of a rack clad construction
Figure 3
Rack rails supporting shuttle cars
Reference to e.g. Industry Code of Practice FEM 9.841 / 10.2.10 “Storage systems with rail dependent storage and retrieval (S&R) equipment – Interfaces”. With the booming e-commerce also the number of racking structures operated by S&R equipment have been exploded.
The design standard “Eurocode 3: Design of steel structures – Part 1-9: Fatigue” provides rules to determine the fatigue resistance for details of steel structures. The S-N curves provided are for welded or bolted connection details as applied in “traditional” structures with steel thicknesses in accordance.
Cold-formed members have a relatively small thicknesses (1 mm – 6 mm) preventing three-dimensional stress distributions. Their connections subjected to fatigue are generally bolted. Therefore, the design rules in EN 1993-1-9 need to be extended to cold-formed structural details.
Figure 4
Load cycle test “wheel on rail”
Figure 5
Pre stretch on coil raw material