Evaluation of Material Properties for Historic Steel Bridges

Evaluating the technical conditions and performance for historic bridges is essential to ensure their structural safety and determine their need for strengthening. This study investigates the first railway steel bridge built in China in 1894, which is listed as a national preservation unit and industrial heritage site. The bridge was not only exposed to years of weather change but also suffered a geological disaster in 1976. In addition, the surroundings have changed, including the construction of new railway lines and scenic areas. Thus, it is imperative to evaluate its technical conditions and performance, particularly its material properties. To this end, evaluation procedures were formulated. First, the material composition, properties, and grades of steel were determined by microstructural analysis: the grade of nonmetallic inclusions in steel was determined by metallographic analysis; the corrosion rate of steel was obtained by electrochemical analysis; and the crystal type, size, element product of the corrosion layer, as well as the fracture type of the steel, were analyzed by phase composition and elemental analysis. Next, the static performance indices of the steel were obtained by mechanical property tests: the hardness value of the steel was obtained from hardness test; the yield and tensile strengths of the steel were obtained from tensile tests; and the fatigue properties of the steel were analyzed through fatigue tests. The S-N curve of the steel was determined by fitting the tested data. This study provides a reference for the evaluation of the technical conditions and performance of historic bridges.