HASHIZUME LUJAN ALEX KAZUO

Quantitative Evaluation of Salt Deposition Effects on Bridge Structures Based on Bridge Shape

Nakamura Fuminori

 Salt transported from the sea affects the degradation of bridge structures differently depending on the parts and materials of the bridge. Therefore, in this study, an investigation is conducted to quantitatively evaluate the salt deposited by numerical analysis based on various bridge sections. The analysis method of this study is divided into two stages. In the first stage, the flow of wind speed near the bridge section was analysed using the open-source software OpenFOAM. Then, using the wind speed field obtained in the first stage, in the second stage, the movement of salt particles was analysed using the random walk method.
 To confirm the validity of the analysis in this study, an experiment was conducted to compare the results with experimental data. A 1/6 scale model of the Aomikawa Bridge was used, and the wind speed was set to approximately 3.5m/s. In the analysis, the dimensions of the analysis area were made the same to reproduce this experiment. By comparing the results of the experiment with the analysis, although there were errors, the overall flow patterns observed in both were consistent. Therefore, the reliability of the analysis was confirmed. A tendency of decreasing wind speed was observed near the model, and large vortices were observed in the upper part of the bridge girder. Similarly, vortices occurred between the main girders in the lower part of the bridge girder. Salt deposition analysis was conducted using the wind speed field.
 Analyses of models 1 to 8 with different cross-sections were conducted, and in models 1 to 4, salt particles were mainly accumulated at the rear of the model, while model 5 with a smoother airflow pattern showed a more uniform distribution. In models 6 and 7, except for the areas before and after where vortices existed in the airflow, there was little noticeable accumulation of salt particles. In conclusion, there was no significant difference in the amount of salt deposited on the entire model or its lower part. Instead, the main difference was found in specific areas where salt particles accumulated, which is believed to be due to their size and shape.