Distortions and residual stresses of NSS, HSS and hybrid box sections with single-bevel butt welds: An experimental study

• A total of nine NSS, HSS and hybrid box sections are analysed. • Ratio of maximum welding-induced compressive strains in the flange and web varies between 0.93 and 1.28. • Maximum out-of-flatness is approximately B /230. • Contour method is used for determining residual stresses. • A novel residual stress model is developed incorporating manufacturing parameters. A comprehensive experimental study, focusing on distortions and residual stresses, is conducted on a total of nine box sections with single-bevel butt welds consisting normal strength steel (S355MC), high strength steel (S700MC), and hybrid (NSS-HSS) sections. Dimensional analysis is carried out and the calculated Rosenthal numbers indicate the use of fast MAG welding heat sources, validating the assumption of uniaxial residual stresses. Strain gauge measurements during welding reveals the ratio of maximum welding-induced compressive strains in the flange and web depending on the width-to-thickness ratio. Measured maximum out-of-flatness is closely matching the B /200 recommendation for equivalent geometric imperfections in panels according to EN 1993–1–5 suggesting that a modification of local imperfection limits in welded box sections is needed. The contour method is successfully used to evaluate manufacturing-induced longitudinal residual stress fields, designating a novel application for box sections. Compressive stresses show a clear decreasing trend with increasing thickness. Furthermore, compressive residual stress variation due to pre-welding manufacturing steps is assessed based on the difference between measured welding-induced and manufacturing-induced membrane residual stresses. In addition, a novel residual stress model is developed for NSS, HSS, and hybrid box sections with single-bevel butt welds, incorporating manufacturing parameters such as heat input, weld seam area, number of weld passes, filler material strength, and steel grades of the base material.