Margad Batbayar

Predictive analysis of salt damage environment around a bridge girder by reproduced a large-scale low-pressure

Fuminori NAKAMURA

In winter, coastal areas are subjected to severe weather conditions and waves due to seasonal winds, resulting in the generation of large amounts of seawater spray and degradation of steel and concrete structures due to salt damage. Previous studies have shown that wind speed, wind direction, and wave conditions affect the amount of seawater spray through observation and analysis, and that numerical analysis can predict the temporal and spatial variations of seawater spray. However, the lack of observed meteorological and wave data around the actual bridge structure presents a problem in accurately predicting the amount of salt spray in the vicinity of the bridge girder.
Therefore, this study aimed to construct a numerical simulation that integrates the effects of meteorological and wave action from large-scale low-pressure systems with the prediction of salt spray on bridge girders. This model considers general bridge shapes and terrain conditions, reproduces the surrounding meteorological, wave, and tidal variations, and integrates the resulting salt spray on the bridge girders.
The validity of the constructed model was verified using the results of a survey of salt spray amounts conducted on the Nadachi Bridge located at Joetsu City, Niigata Prefecture, during the period from February 18 to 19, 2018, when a large low-pressure system occurred.
The calculation results of the prediction model were found to be generally consistent with the observed values for a previous large low-pressure system in terms of wind speed, wave height, and tidal level, and the variations of wind and wave conditions over time were reproduced. Furthermore, the calculation results of salt spray on the bridge girder reproduced the spatial distribution of wind and salt concentrations. The boundary conditions for wind, wave height, and tidal level that act on the bridge girder significantly depend on the salt concentration, and the results showed that if the boundary conditions are accurately calculated, the temporal variations of salt concentrations around the structure can be predicted sufficiently.
In conclusion, the use of a model to predict large-scale low-pressure systems enabled detailed predictions of meteorological and wave actions. Furthermore, using these predictions as boundary conditions allowed for the prediction of salt spray around coastal concrete structures.