Modeling of stress-strain relationship of advanced high-strength cold-formed steel at elevated temperature

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Recent material advances in the steel manufacturing processes have led to materials with greatly enhanced capabilities at competitive cost. New grades of cold-formed steels, referred to as Advanced High-Strength Steels (AHSS), have been developed with yield strengths up to 1200 MPa and ultimate strengths up to 1900 MPa. However, the behavior of these novel materials must be understood and characterized under extreme environments which may arise in structural applications, including high temperatures resulting from fire. In most current design codes, including the American Iron and Steel Institute standard, Eurocode and the Australian Standard, the properties of high strength cold-formed steel subjected to fire conditions are limited or non-existent. A series of steady-state coupon tensile tests for two families of AHSS with nominal yield strength of 340 MPa, 700 MPa, 1030 MPa and 1200 MPa at various uniform temperature stages from ambient to 700 C were carried out. A new constitutive model was proposed based on the characteristics of AHSS stress-strain curves from the tests, and a good agreement between the test data and the model was achieved. In addition, existing stress-strain models from previous studies were investigated to represent the material properties of AHSS at elevated temperatures and compared with the updated model. The fittings of the multiple material models for various families and grades of AHSS were evaluated. 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.