Abstract

To achieve sustainability in bridge design, it is critical to ensure both economic viability and low environmental impact. While stainless steel has great mechanical properties and life cycle performance, the material is expensive, which has limited its use in bridges. This research aims at exploring the benefits of using stainless steel corrugated web girders as an alternative to carbon steel flat web girders in composite road bridges. This concept is expected to lower the investment cost, which enables a broader utilization of the good properties offered by stainless steel. A genetic algorithm optimization routine has been developed to produce bridge designs with minimum weight, investment cost, life cycle cost (LCC), or life cycle impact. Multiple parametric studies are conducted using a simply supported reference bridge. The optimal design solutions are compared for two main design alternatives: conventional S355 flat web girders and duplex (EN 1.4162) corrugated web girders. The parametric studies consider the effects of different design parameters, including the span length, available girder depth, average daily traffic (ADT) with the corresponding indicated number of heavy vehicles in the slow lane , and the paint maintenance schedule, on the optimal solutions. Furthermore, a sensitivity analysis is carried out to analyse the impact of inflation and discount rates on the obtained results. The results show that the concept of stainless steel corrugated web girders offers significant potential LCC and environmental impact saving for the examined span lengths, particularly in the case of deeper girders, high ADTs, and more intensive maintenance activities. Also, despite the influence of inflation and discount rates on LCC results, the studied concept consistently demonstrated favorable results.

Introduction

Nowadays, sustainability is a priority in the design, construction, and maintenance of civil engineering structures [1]. The United Nations established the 2030 Agenda for Sustainable Development in 2015, along with 17 Sustainable Development Goals (SDGs) [2]. The SDGs address urgent and crucial concerns that humans are currently confronted with, such as climate change and resource depletion [2]. The Communication “Next Steps for a Sustainable European Future” makes it clear that the European Union (EU) prioritizes the transition to a sustainable society [3]. One of the biggest obstacles for the EU in achieving its aim of reducing climate change is mitigating the environmental impacts of buildings and construction. The construction and building sector in the EU accounts for around 40% of total energy final consumption, 35% of greenhouse gas emissions (GHG), and more than 50% of all extracted materials [4]. Furthermore, the construction industry generates a large amount of waste, accounting for one-third of the EU’s yearly waste creation [5].

The bridge industry has shown growing interest in sustainable development, particularly in light of its huge potential impacts on the economy and environment [6]. Composite bridges are well-known bridge types, usually designed with steel girders having flat webs (Fig. 1a) and connected to a concrete deck using shear studs. The shear studs allow composite action and enable the best possible utilization of the two materials [7]. The steel girders are typically made of conventional carbon steel, which is prone to corrosion and necessitates frequent maintenance in the form of inspection, repainting, and replacement throughout its service life. In addition to the costs of these activities, the impact on the environment and the disruption of traffic during the maintenance work are considerable [8].

To mitigate the problems associated with maintenance activities, stainless steel is a good solution. Corrosion resistance is the main justification for using stainless steel [9]. The high durability and corrosion resistance of stainless steel can be utilized to minimize the need for maintenance during the bridge’s design life, leading to a lower life cycle cost. The term “stainless steel” refers to a group of alloys with at least 10.5% chromium that, when exposed to water and oxygen, forms a protective layer against corrosion. Duplex stainless steels are the most commonly used type in bridge applications because of their excellent strength and corrosion resistance [1]. Duplex stainless steel is composed of austenite and ferrite. Ferrite increases strength, whereas austenite is ideal for structural applications because of its ductility, toughness, and excellent corrosion resistance [10]. Not only that but also duplex stainless steel has a comparable or higher strength-to-weight ratio compared to carbon steel. In addition, stainless steel’s improved fire resistance makes it useful for civil engineering applications [11].

Results and discussion

The design of all bridges in the parametric study was governed by either ULS or FLS criteria, specifically related to welded vertical stiffeners (detail C for flat web and detail D for corrugated web, Fig. 4). SLS criteria only governed in cases with limited height (ID14 and ID16). The following sections will present the results of the parametric study, focusing on the examined parameters.

۶٫۱٫ Optimization objective
As mentioned in Section 5, as the first step in the parametric studies, the influence of the optimization objective on the design solution is studied. This is done on the reference case study bridge made of flat-web S355 girders, ID 1–۴, and corrugated-web duplex girders, ID 5–۸٫ The results are presented in Fig. 5.