Elevated temperature and post-fire stress-strain modeling of advanced high-strength cold-formed steel alloys

Advanced high-strength cold-formed steels (AHSS) have been developed with yield strengths up to 1250 MPa and ultimate strengths up to 1900 MPa. Accurate stress-strain modeling of these new steel alloys are required for eventual application of AHSS into the building construction industry, including the material behavior of AHSS subjected to elevated temperatures. A series of new constitutive material models are proposed based on the experimental AHSS stress-strain database at elevated temperatures (i.e., steady-state and transient-state test methods) and post-fire scenario (i.e., residual test method). The stress-strain curves from experiments on two families of AHSS, including dual phase steel with nominal yield strengths of 340 MPa and 700 MPa, and martensitic steel with nominal yield strengths of 1030 MPa and 1200 MPa, reported in a previous study are considered. Existing stress-strain models are investigated and fit to the AHSS database, in addition to the development of new material models. The required input parameters of the proposed stress-strain models are determined, and their corresponding predictive expressions are proposed. It is shown the stress-strain behaviors of AHSS could be accurately described by the proposed models. The data generated by this research addresses fire safety design and will be essential in supporting the adoption of these next-generation steels in future infrastructure.