Design of cold-formed beam-columns restrained by sheeting

The load-bearing capacity and behaviour of laterally braced cold-formed sections has been studied in this project. The test program comprised 28 loading tests on cold-formed purlins continuously braced by trapezoidal sheeting and two tests where the purlins were connected to the gypsum board. The aim of the tests has been to determine the behaviour of single span purlin systems in combined compression and bending. The test program consists of centric and eccentric compression, bending with uplift and gravity load and combined compression and bending tests. A total of seven load cases for each of U-, C-, Z- and /sigma/-profiles were carried out. The test results are compared to design procedures determined by Eurocode 3 (1993), design of steel structures, draft annex A (part 1.3). The Eurocode 3 design method appears to give better results for C- and Z-profiles than for U- and /sigma/-profiles. It is also shown that the calculated ultimate loads according to Eurocode 3 are on average 62% conservative compared to tested results. The main reason for conservatism is in the effective length determination for the free flange. The fixed end boundary conditions used in VTT's tests are not included in the design expressions of Eurocode 3. The effective length for a beam on an elastic foundation with concentrated and distributed axial loading is derived using an energy method. The derived effective lengths are used with the Eurocode 3 design method. The use of correct effective lengths results in an average conservatism of 23 % in the design method. However, when the inelastic buckling of the free flange determines the ultimate load, the average conservatism is about 31%. The comparison is made between test and calculated characteristic resistance. Therefore the partial safety factor /gamma/M1 is set to 1.0. The accuracy of geometrically and materially non-linear finite element analysis of the /sigma/-profile is also verified. An example, where calculation of the C-profile according to Eurocode 3 is made, is included