Investigations for structural safety assessment of corroded cast iron bridge piers

Cast iron bridge piers, often more than 100 years old, are still in service in rail and road bridges in many parts of Australia. Increasingly, the effect of corrosion on their present and future structural safety is of interest. Field investigations and observations to assess corrosion losses and pitting of the cast iron piers of four different operational railway bridges located in tidal marine exposure conditions are described, noting that direct visual examination usually is rendered difficult by immersion, marine growth and the presence of the graphitised layer. Measured corrosion losses and pit depths showed considerable variability between piers and between bridges. Evidence was found for the influence of microbiological corrosion, fostered by nitrogenous pollution. Implications for structural safety assessment are discussed and an example given of the estimation of likely future rate of (long-term) corrosion, necessary for assessment of remaining structural safe life.