Keito NAKAJIMA

Study on Buckling Strength Formula of Truss Bridge Compression Diagonals with Corrosion Breaks on Two Edges

Eiji IWASAKI

 In the cross sections of the diagonal members of truss bridges, if corrosion progresses, the fillet welds may separate, leading to corrosion break. The previous study proposed a buckling strength formula to evaluate the buckling strength of diagonals containing a single corrosion break. However, this formula cannot be applied when two corrosion breaks are present.
 To resolve this issue, this study proposes a buckling strength formula that can evaluate the buckling strength of diagonals containing corrosion breaks on two edges.
 First, FEM analysis was carried out on plates containing corrosion breaks on two sides, based on the following parameters, corrosion break length ratio (a/b), width-to-thickness parameter, and corrosion break center distance ratio (d/a). From these analyses, it was found that when d/a exceeds 1, the buckling strength is equivalent to that of a plate containing a single corrosion break, whereas when d/a is less than 1, the buckling strength decreases. Therefore, a regression analysis was conducted, and a local buckling strength formula was proposed for plates containing corrosion breaks on two sides, in which buckling strength of a plate with d/a equal to 0 is multiplied by the multiplier α.
 Second, FEM analysis was carried out on diagonals containing corrosion breaks on two edges, where d/a was set to 0. The results showed that the existing coupled buckling strength formula cannot accurately evaluate the buckling strength of such diagonals. Also, a new coupled buckling strength formula was proposed for diagonals containing corrosion breaks on two edges, in which overall buckling strength is multiplied by the correction factor Q' based on average local buckling strength Q.
 Finally, a comparison with FEM analysis results confirmed that this method can evaluate the buckling strength of diagonals containing corrosion breaks on two edges with an accuracy within 10% of the yield strength.