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Research on post-fire mechanical properties of thin-walled cold-formed steel and its influence on the Σ-shaped columns after fire exposure.

Authors :
Luo, Kai
Li, Haifeng
Yang, Jingjie
Kang, Haixin
Yan, Fengzuo
Han, Xue
Source :
Thin-Walled Structures. Nov2024, Vol. 204, pN.PAG-N.PAG. 1p.
Publication Year :
2024

Abstract

• 144 tensile tests were conducted on post-fire thin-walled cold-formed steel, considering different steel grades, thicknesses, heating temperatures, and specimen locations. • The prediction formula of the post-fire elastic modulus, yield strength, and ultimate strength were developed based on the test results. • Numerical models of cold-formed steel columns were developed and verified against available tests, and parametric analyses were performed to investigate the post-fire behavior of the cold-formed steel columns by importing post-fire material properties. • The applicability of the direct strength method for the post-fire load-bearing capacity of cold-formed steel columns was assessed based on the parametric analysis results. This paper conducts a comprehensive investigation into the post-fire mechanical properties of thin-walled cold-formed steel (CFS) and evaluates the design method for the post-fire load-bearing capacity of CFS lipped channel section with web stiffener (Σ-shaped) columns. A total of 144 tensile tests were conducted to determine the mechanical properties of CFS after exposure to heating treatment. The study considered the effects of varied material strengths (Q235 and Q420), plate thicknesses (1.5 mm and 2.5 mm), extraction positions (flat plate, 90° corner, and 45° corner), as well as heating temperatures ranging from 20 °C to 800 °C. The research indicates that the heating temperature does not have a prominent influence on the elastic modulus of CFS, whereas its impact on yield strength is pronounced. After exposure to 800 °C, the yield strength of CFS can be reduced by 40 %, but the strain-hardening effect by cold-working still existed, which enhanced the yield strength by up to 20 %. This paper presents a predictive formula for the reduction factor of the mechanical properties. To assess the influence of post-fire mechanical properties on the load-bearing capacity of CFS columns, a finite element model of Σ-shaped columns was developed and calibrated. The simulation results indicate that the post-fire strain-hardening effect at corners would enhance the load-bearing capacity by less than 6 %. Finally, based on a parametric analysis, it was demonstrated that the Direct Strength Method (DSM) applied for distortional-local interaction buckling columns was still effective once the post-fire mechanical properties were incorporated when slenderness factor λ dl > 1.5. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
02638231
Volume :
204
Database :
Academic Search Index
Journal :
Thin-Walled Structures
Publication Type :
Academic Journal
Accession number :
179603259
Full Text :
https://doi.org/10.1016/j.tws.2024.112315