Steel box sections can be found in a wide range of structural applications including bridges, buildings, industrial plants and resources equipment. The sections are usually fabricated from flat plates which are welded at the corners. The welding process can introduce residual stresses and geometric imperfections into the sections which are known to have an influence on their strength. For some thin-walled sections, large periodic geometric imperfections have been observed in manufactured sections. Subsequent investigations have indicated that the imperfections are in fact buckling deformations i.e. the box section has buckled due to welding residual stresses prior to any application of external load. The behaviour of the box sections has been modelled using a finite element analysis that accounts for both geometric and material non-linearities. The welding procedure has been modelled including the cooling process around the heated area due to welding. Tests have been carried out on box sections with a range of width to thickness ratios for the plate elements. Using calibration with the test results, simulation studies have been performed to determine the initial "stress-free" imperfections prior to welding. Modelling was shown to give good correlation with the test results. The conditions for buckling to take place as a result of the welding process have been established. The influence of welding buckling deformations on subsequent loading strength has been examined theoretically and experimentally and design recommendations have been made.
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