Determination of initial geometric imperfections in the flanges of stainless steel corrugated web I-Girders using distributed optical fibre sensing

Artikel i vetenskaplig tidskrift, 2026

Geometric imperfections significantly influence the local flange resistance of plated structures, including corrugated web I-girders; however, reliable methods for their characterization and modelling remain limited. This study investigates different approaches for representing initial imperfections and their influence on the moment resistance of corrugated web girders through a full-scale four-point bending test on a stainless steel specimen. Prior to testing, the central corrugated web segment was captured using 3D scanning to obtain the as-built geometry, while distributed optical fibre sensing (DOFS) sensors recorded strain distributions on the upper surface of the top flange during loading. The scanned geometry was incorporated into a geometrically and materially nonlinear finite element (FE) model, which was validated against the experimental load–displacement response and measured strain fields. In parallel, simplified shell models employing eigenmode-based imperfections with amplitudes derived from the 3D scan, DOFS measurements, and the Eurocode recommendation of cf/50, wherecf denotes the maximum flange outstand, were evaluated. The results demonstrate that the scan-based solid model accurately reproduces both the global and local structural responses, whereas shell models using imperfection amplitudes directly obtained from the 3D scan or the Eurocode recommendation significantly underestimate the ultimate resistance. Improved predictions were achieved by isolating the local flange imperfections associated with the corrugation from the global initial imperfections. Based on the observed correlation between distributed strain profiles and local geometric deviations, an analytical expression is proposed for estimating local imperfection amplitudes from DOFS measurements. Although demonstrated for the investigated specimen, the results indicate that DOFS provides a practical means of estimating representative imperfection amplitudes for advanced FE modelling and highlight that local undulating flange imperfections associated with the corrugated web govern the flange local buckling resistance.