Mechanical properties and design recommendations of very high strength steel S960 in fire

• Mechanical properties of VHSS S960 at elevated temperature are obtained.
• Elevated-temperature mechanical properties of steels are dependent on steel grades.
• No current design standard is applicable to VHSS S960 at elevated temperatures.
• Accurate predictive equations are proposed for evaluating VHSS S960 in fire.
• Research results offer information for revision of current design standards.

Due to the lack of experimental evidence in literature and specific provisions in current leading design standards for (very) high strength steel structures, the fire-resistance design of steel structures with high strength steel (HSS) and very high strength steel (VHSS) is either too conservative or safety-compromised in practice, which seriously retards the application of HSS and VHSS in civil engineering as well as leads to safety risk. This paper presents a detailed experimental study on VHSS S960, under both steady state fire condition and transient state fire condition. The elastic modulus, yield strength and ultimate strength of S960 in fire are obtained and compared with the recommendations of leading design standards for steel structures (i.e. EC3, ASCE, AISC, AS 4100 and BS 5950), as well as with HSS S460 and S690 reported in previous study. The comparison with design standards reveals the necessity of including specified recommendations on the deterioration of mechanical properties in fire for very high strength structural steels in current leading design standards. Further, some unique predictive equations are proposed for the elevated-temperature mechanical properties of VHSS S960. The research results could be employed as fundamental data to numerically or theoretically analyze the fire performance of steel structures with members made of S960 and to carry out accurate fire-resistance design.