Stainless Steel Corrugated Web Girders for Composite Road Bridges: Concept Evaluation and Flange Buckling Resistance

Sammanfattning: Achieving a sustainable bridge design requires careful consideration of economic viability and environmental impact over the entire lifespan of the structure. While stainless steel is recognized for its excellent life cycle performance, its high cost prevents it from being used to a larger extent in bridges. In this thesis work, a new solution is investigated to mitigate this issue. The new solution comprises the use of corrugated webs in stainless steel girders which is expected to result in reduced material consumption and cost. The work in this thesis focuses on two problem areas in this field. First, a study is performed to examine the competitiveness of the new concept in relation to conventional designs of steel-concrete composite road bridges. The second part of the work focuses on the problem of flange buckling in girders with corrugated webs. Previous research has shown that the design models developed for flange buckling resistance, including the one in EN 1993-1-5, frequently result in unsafe design. Furthermore, these models were developed for carbon steel and have not been updated for stainless steel. To explore the economic and environmental benefits of the new concept, two studies have been conducted. Firstly, three design solutions are examined on a case study bridge with three continuous spans. These design solutions include carbon steel flat web, stainless steel flat web, and stainless steel corrugated web girder bridges. A genetic algorithm is used to optimize each design solution in terms of weight. The three optimal solutions are then assessed in terms of investment costs, life cycle costs (LCC), and environmental life cycle impact. Secondly, two of the considered design solutions, namely carbon steel flat web and stainless-steel corrugated web girders, are employed to conduct multiple parametric studies using a simply supported reference bridge. For both design solutions, the effects of optimization targets on weight, investment cost, life cycle cost, and environmental life cycle impact are initially investigated. Following that, the focus is put on the life cycle cost (LCC) as an optimization target, and the impact of various design input parameters is investigated. These parameters include span length, girder depth, average daily traffic (ADT) with the associated number of heavy vehicles per slow lane (Nobs), and time intervals and expenses for maintenance activities. Furthermore, a sensitivity analysis is conducted to study the influence of the inflation rate and discount rate. The results indicate that the new concept offers considerable potential saving in weight, life cycle costs, and life cycle impacts for both simply supported and continuous bridges. The saving is more apparent with deeper girders, higher ADT, and more intense maintenance activities. Saving is also larger when inflation is high and discount rate is low. After studying the potential of corrugated web girders to reduce costs and environmental impacts in the case of employing stainless steel, a study of the flange buckling behaviour in duplex stainless-steel girders is conducted in this work. A parametric finite element model is developed and validated with tests conducted on beams made of carbon steel. The material is then changed to EN1.4162, and linear buckling analysis (LBA) and geometrically and materially nonlinear analysis with imperfections (GMNIA) are carried out on 410 girders with typical bridge girder dimensions. The results are compared to previously developed models for carbon steel, and a new buckling curve and flange local buckling design procedure for duplex stainless-steel girders with corrugated webs are proposed. The study shows that the new proposed design model generates more accurate estimates of flange buckling resistance than previous proposed models.