Risk assessment of steel bridges under the influence of changing environmental conditions

Corrosion is a commonly observed deterioration mechanism in metallic bridges, resulting in loss of material with time, which may lead to impaired performance and premature in-service failures. A number of factors are known to influence the initiation and subsequent rate of corrosion in metallic bridges, including climatic parameters such as relative humidity and temperature, atmospheric pollutants (e.g. SO2) and high airborne salinity. These factors and their interactions may have a detrimental influence on the rate of corrosion. Alterations of the exposure conditions, for instance due to climate change or/and adoption of government policies related to the levels of atmospheric pollutants, are likely to influence the long-term corrosion rates in metallic bridges. This paper presents a methodology, based on reliability analysis, for the time-dependent risk assessment of corroding metallic railway bridges, considering the impact of long-term changes in climatic and atmospheric pollutant variables. The evolution of variables related to the deterioration process (e.g. climatic parameters, atmospheric pollutants, etc) and bridge resistance variables are treated as random using suitable distributions. The time evolution of the probability of failure of the bridge is quantified through Monte Carlo simulation and this is then extended into risk by considering the consequences of bridge failure. The procedure is demonstrated through a case study using a steel railway bridge. Results are presented for the moment-capacity limit state of the bridge, considering a number of emission scenarios based on UKCP09 climate projections and assumed changes in the concentrations of atmospheric pollutants