Stress-strain models of high performance steels and concrete after exposure to elevated temperatures

Steels and concrete are most used materials in civil engineering structures. In recent years, high performance steels including high strength steels (HSSs) and stainless steels are increasingly used to reduce the consumption of materials and increase the durability of structures. A number of stress-strain models are available for stainless steels at ambient temperature. However, versatile models for high strength steels have not been found in literature. Although high temperatures can cause severe damage to steels and concrete, most of constructional structures do not collapse during a fire. To evaluate structures after a fire, accurate stress-strain models are required. However, information of stress-strain models after fire exposure is limited. In this study, stress-strain models for high strength steels at ambient temperature are proposed. To investigate the post-fire behaviour, high strength steels, stainless steels and concrete are heated to high temperatures and cooled to room temperature to simulate the fire in a real scenario. Afterwards, post-fire mechanical properties are experimentally investigated, and the stress-strain models are developed. High strength steels might exhibit continuous or discontinuous yielding in their stress-strain relation response at ambient temperature, depending on the chemical composition, manufacturing process and procedure. However, no criterion has been proposed in the literature to predict the occurrence of a yield plateau. Meanwhile, high strength steels often have limited ductility, making it important to predict their fracture for a safe design. But no existing stress-strain models have this desired feature. To allow the development of versatile stress-strain models for high strength steels, stress-strain curves and chemical compositions are collected from the open literature. In addition, experimental investigations are conducted on two types of Australian high strength steels. From the analysis of the test data, a criterion is proposed to determine the occurrence of the yield plateau based on the steel strength and carbon content. Two stress-strain models are then proposed for high strength steels exhibiting continuous and discontinuous yielding, respectively. In this study, extensive experimental investigations on high strength steels, stainless steels and concrete are conducted and a large amount of test data are collected in open literature. Stress-strain models for high strength steels at ambient temperature, and the post-fire models for high strength steels, stainless steels and concrete, are proposed. These models can be used to facilitate a more accurate evaluation and a safer design for civil engineering structures