Behaviour of ultra-high-strength concrete-filled double-skin tubes under elevated temperature

This paper provides a comprehensive study of the behavior of ultra-high-strength concrete-filled double-skin tubes (CFDST) at elevated temperatures. Material constitutive models for various materials, including high-strength steel (HSS), stainless steel, and different concrete grades, are examined and refined for better simulation of such members under elevated temperatures. Firstly, a finite element (FE) model is developed and verified against extensive test results. An innovative automatic algorithm is then employed to create meticulously verified FE results. Through a systematic parametric study, the research aims to enhance understanding of the fire performance exhibited by CFDST columns. As a result, design recommendations are presented concerning the preferred material arrangement for the inner core and outer ring using the analyzed materials for metal tubes and filling concrete. Utilizing high-strength materials for the inner core with a specified diameter ratio (i.e., D_in / D_out) is preferred for higher member capacity. Finally, a proposed design method, complying with existing codified methods, is examined and proven to be efficient and reliable.