American Society of Civil Engineers


Service Life Prediction for Weathering Steel Highway Structures


by Neal Damgaard, (University of Waterloo, Waterloo ON, Canada E-mail: ndamgaar@uwaterloo.ca) and Scott Walbridge, (University of Waterloo, Waterloo ON, Canada E-mail: swalbrid@uwaterloo.ca)
Section: Steel Bridge Issues, pp. 1-10, (doi:  http://dx.doi.org/10.1061/41031(341)240)

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Document type: Conference Proceeding Paper
Part of: Structures Congress 2009: Don’t Mess with Structural Engineers: Expanding Our Role
Abstract: Composite concrete and steel slab-on-girder systems are used for the superstructures of highway structures, including underpasses and overpasses, throughout North America. In certain jurisdictions, it has been reported that large numbers of these structures show evidence of serious corrosion in the webs and the bottom flanges of the girders. The cause of the corrosion is believed to be a combination of moisture from melting snow, road salt, and sulphur dioxide. In a number of observed cases, the most heavily corroded regions of these bridges appear to coincide with the splash zones that are present due to the passage of large trucks. In order to facilitate the probabilistic structural analysis of these deteriorating structures, an analysis program has been developed, which enables the calculation of their diminishing structural reliability with the passage of time. Specifically, the effects of corrosion on the shear, moment, and bearing resistance of the girders are evaluated in accordance with the limit states outlined in the Canadian Highway Bridge Design Code [1]. Statistical distributions are then applied to the load- and resistance-related input parameters, including those associated with various corrosion models. A Monte Carlo simulation is then performed to generate curves of bridge reliability versus time for various assumed corrosion rates. The focus of this study is lifespan prediction of weathering steel highway structures. Weathering steel is a type of high-strength, low-alloy steel which has been found to behave favourably with respect to atmospheric corrosion resistance. The steel contains small amounts of nickel, chromium, and copper; it is available as Type A or Type AT, as designated in CAN/CSA G40.21-M92 [2]. Under repeated cycles of wetting and drying, weathering steel forms a thin, adherent oxide patina, which afterwards protects it from further penetration of oxygen and moisture that leads to corrosion. This patina is supposed to form in 18 to 36 months [2].


ASCE Subject Headings:
Service life
Predictions
Steel structures
Highway and road structures