Experimental Study on the High Temperature Properties of Advanced High-Strength Cold-formed Steels

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Recent advances in steel manufacturing have led to materials with greatly enhanced capabilities at competitive cost. New types of steel, referred to as Advanced High-Strength Steels (AHSS), have been developed for automotive applications with yield strengths up to 1200 MPa, ultimate strengths up to 1900 MPa, and relatively large tensile elongations. Efficiently harnessed, the adoption of AHSS materials in the construction industry can provide many benefits, notably with cold-formed steel structures which provide efficient, lightweight, and resilient solutions for a range of building applications. However, the behavior of these novel materials still needs to be characterized under extreme environments which may arise in structural applications, including high temperatures resulting from fire. To fill this gap, an experimental investigation was carried out on the mechanical properties at elevated temperature and after cooling down of six different steel grades. The tested materials included dual-phase steel (DP), martensitic steel (MS), and high-strength low-alloy steel (HSLA) with nominal yield strengths ranging from 340 to 1200 MPa and nominal ultimate strengths ranging from 480 to 1500 MPa. Three types of high temperature regimes, namely steady-state, transient-state, and residual tests, were applied at temperatures up to 700°C. Material properties were obtained including elastic modulus, yield stress, and ultimate stress. The test results were compared with the prediction models in Eurocode 3 and AISC 360, and other published test data. Comparisons showed that AHSS steels exhibit larger reduction in stiffness and strength than lower grade cold-formed steels at elevated temperature and after cooling down.