Optimized design and life cycle cost analysis of a duplex welded girder bridge

Stainless steel, as a Chromium-Nickel (Cr-Ni) alloy, has recently become a popular construction material owing to the combination of excellent corrosion resistance and mechanical strength. In particular, duplex grades, with a balanced austenite ferrite microstructure, show greater proof strength and ductility than that of standard austenitic stainless steel groups. Over the last decade, those grades were often used in bridges in corrosive environments. The increased interest in stainless steel is also due to recent research demonstrating the good fatigue resistance of duplex welded components, raising an even higher interest in bridges made of these grades. The EN 1.4162 and 1.4062 duplex grades are characterized by a lower Nickel and Molybdenum content which results in a more stable cost, but at the same time more prone to pitting corrosion. In mildly corrosive environments, they can be a good alternative to protected carbon steel (regarding maintenance) or austenitic grades (regarding initial price). Additionally, reference research today exists proving that those grades have comparable corrosion resistance to the austenitic stainless steel grades EN 1.4307 and EN 1.4404. The ultimate objective of this study is to calculate the possible weight reduction in an existing carbon steel girder bridge, when lean duplex welded components are used. The benefit from the greater mechanical properties of the latter are considered according to the latest version of EN 1993-1-4 (2015). The fatigue design is made using the hot-spot stress method combined with finite element models to assess the local stress distribution, considering eight critical details along the girder. The fatigue life of all the considered details were found to be satisfactory with a higher number of loading cycles than the design value proposed by EN 1993-1-9 (2005). Conclusions were also drawn upon the influencing finite element parameters on the evaluation of hot spot stress via sensitivity analysis. Based on previous published research on the life cycle cost assessment of painted and hot-dip galvanized steel bridges, the initial costs of the carbon and the stainless steel option are compared, as well as the total Net Present Value at the life horizon of the bridge.