Stainless Steel Corrugated Web I-Girders for Composite Road Bridges

Doktorsavhandling, 2025

Achieving a sustainable bridge design requires a comprehensive evaluation of both economic feasibility and environmental impact throughout the structure’s lifespan. While stainless steel is widely recognized for its superior life cycle performance, its high cost has limited its broader application in bridge construction. This thesis investigates a new design solution comprising stainless steel corrugated web I-girders for composite road bridges. This design solution is expected to reduce material usage and compensate for the higher cost of stainless steel, making it a more viable option for bridge girders.

The thesis is structured around three key areas of investigation. First, a comparative study is conducted to evaluate stainless-steel corrugated web girders against conventional carbon steel flat web girders. Second, the issue of flange buckling in stainless steel corrugated web I-girders is studied, noting that EN 1993-1-5 often yields unsafe predictions for carbon steel and has not been updated for stainless steel. Third, a fatigue assessment of the fatigue-prone welded detail between the corrugated web and the flange is conducted, noting that current design standards like EN 1993-1-9 do not categorize this detail, and that no fatigue test data exists for stainless steel.

In concept evaluation, two design solutions—carbon steel S355 with flat web and stainless steel EN1.4162 with corrugated web I-girders—are compared through parametric studies using a simply supported reference bridge. A design optimization tool employing genetic algorithm is developed and employed to optimize each design solution concerning weight, investment cost, life cycle cost (LCC), or environmental impact. The results showed that the new concept can be realized with a moderate increase in investment cost, bridging the cost gap between carbon and stainless steel, while offering lower life cycle costs and reduced climate impact compared to the traditional concept—particularly for bridges with deeper girders, higher average daily traffic, and more intense maintenance activities.

With reference to the flange buckling behaviour, a parametric finite element model is developed and validated. A linear buckling analysis (LBA) and geometrically and materially nonlinear analysis with imperfections (GMNIA) are carried out on 410 girders. The results are compared to previously developed models for carbon steel, and a buckling coefficient factor, together with a new buckling curve, is proposed.

The fatigue of the flange-to-web welded detail is examined through both numerical and experimental studies. Initially, critical load effects at the corrugation corner—the crack initiation location—are identified, including membrane stress and stresses due to transverse flange bending. Subsequently, the combination of these effects in fatigue design is discussed. Additionally, 86 fatigue test results on carbon steel corrugated web members are compiled and categorized by the corrugation angle. Statistical analysis is conducted, and four detail categories (DCs) are proposed for carbon steel.

Finally, to assess the applicability of the proposed detail categories to duplex stainless steel, 15 stainless steel (EN 1.4162) beams with different corrugation angles were tested under cyclic loading. The cracking modes were documented, followed by a statistical analysis and comparison with carbon steel. The tested beams demonstrated fatigue strength comparable to their carbon steel counterparts. In addition, a fatigue assessment using the Hot Spot Stress (HSS) and Effective Notch Stress (ENS) approaches was conducted. The HSS method with DC100 and the ENS method with DC225, both based on the maximum principal stress, provided conservative estimates of the fatigue strength of the tested beams.