In this study, fracture toughness of existing steel highway bridge members was investigated by CTOD and Charpy Impact tests, and critical crack length, at which fatigue crack shifts to the brittle fracture, was discussed. Critical CTOD value, δc became 0.058mm(-30℃) and 0.027mm(-50℃) based on the lower value obtained by the CTOD tests (4 bridges) and Charpy impact tests (13 bridges). Based on δc, critical crack length was estimated for fatigue crack growth at web gusset welded joints of steel I-girder bridges.
