Fatigue failure of 350WT steel under large-strain seismic loading at room and subfreezing temperatures

Abstract

Due to its high ductility, weldability and toughness at low temperature, CSA G40.21-350WT steel in Canada is primarily used in bridge construction, ship building, and seismic energy dissipation systems. This article presents uniaxial tensile tests and constant- and variable-amplitude cyclic testing performed on 350WT steel at room and subfreezing temperatures. The variable-amplitude tests include common step-loading patterns as well as tests under strain signals obtained from the brace response in building structures subjected to three different types of earthquakes. The ductility of 350WT steel from monotonic tensile tests is essentially same at room and low temperatures (−40°C). The cyclic test results revealed that cold temperatures as low as −35°C did not have adverse effects on the low cycle fatigue life of 350WT steel. The benchmark constant-amplitude tests were employed to predict fatigue life under different large-strain variable-amplitude loading patterns both for room and subfreezing temperature conditions. In addition to the common strain-life approach, the adequacy of two well-established energy-life models for predicting fatigue life under variable-amplitude loading was evaluated. The strain-life approach generally performed better than the energy-life methods, particularly for step-loading histories. Comparison between predictions and laboratory observations showed that the fatigue failure life under large strain seismic loading can be accurately estimated, especially at room temperature.