Experimental Study on Fatigue Strength of Corroded Bridge Wires

摘要

Fatigue tests were conducted for corroded galvanized steel wires on three corrosion levels, showing that fatigue strength of corroded wires lowers as corrosion progresses. Corrosion pits were measured on the corroded specimens, showing severer corrosion produced deeper pits in more condensed areas. Fatigue tests were then conducted for wire specimens with artificial pits whose sizes were decided by the measured corrosion pit data. Three different pit shapes were assumed: round, triangle, and triangle with a notch. The wire specimens with round pits did not break until 1 million cycles in the stress range of 400 MPa. The fatigue strength of wires with the triangular pit was lower than that with a round shape. Triangular pit specimens broke at fewer cycles for shorter pit length. The fatigue strength of wires with a notched triangle further decreased, and critical cycles did not depend on pit length. As the S-N relation of the wire specimens with triangular pits and notched triangular pits has a similar tendency as those of the actually corroded wires, the pit shape seems to be a dominant factor in lowering fatigue strength. The stress concentration factor at the sharp edge of the pits were obtained by strain gauge measurement and FEM analysis. Both methods showed that the stress concentration is larger for sharper pit shapes, indicating that this is the major cause for the decrease of fatigue strength.