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Steel and Composite Structures
  Volume 38, Number 2, January25 2021 , pages 121-139
DOI: https://doi.org/10.12989/scs.2021.38.2.121
 


Behaviour of ultra-high strength concrete encased steel columns subject to ISO-834 fire
Yong Du, Huikai Zhou, Jian Jiang and J.Y. Richard Liew

 
Abstract
    Ultra-high strength concrete (UHSC) encased steel columns are receiving growing interest in high-rise buildings owing to their economic and architectural advantages. However, UHSC encased steel columns are not covered by the modern fire safety design code. A total of 14 fire tests are conducted on UHSC (120 MPa) encased steel columns under constant axial loads and exposed to ISO-834 standard fire. The effect of load ratio, slenderness, stirrup spacing, cross-section size and concrete cover to core steel on the fire resistance and failure mode of the specimens are investigated. The applicability of the tabulated method in EC4 (EN 1994-1-2-2005) and regression formula in Chinese code (DBJ/T 15-81-2011) to fire resistance of UHSC encased steel columns are checked. Generally, the test results reveal that the vertical displacement-heating time curves can be divided into two phases, i.e. thermal expansion and shortening to failure. It is found that the fire resistance of column specimens increases with the increase of the cross-section size and concrete cover to core steel, but decreases with the increase of the load ratio and slenderness. The EC4 method overestimates the fire resistance up to 186% (220 min), while the Chinese code underestimates it down to 49%. The Chinese code has a better agreement than EC4 with the test results since the former considers the effect of the load ratio, slenderness, cross section size directly in its empirical formula. To estimate the fire resistance precisely can improve the economy of structural fire design of ultra-high strength concrete encased steel columns.
 
Key Words
    concrete encased steel column; ultra-high strength concrete; ISO-834 fire; failure mode; fire resistance; design code
 
Address
Yong Du: College of Civil Engineering, Nanjing Tech University, Nanjing, China;
International Centre of Integrated Protection Research of Engineering Structures, Nanjing Tech University, Nanjing, China
Huikai Zhou: College of Civil Engineering, Nanjing Tech University, Nanjing, China
Jian Jiang: School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou, China
J.Y. Richard Liew: College of Civil Engineering, Nanjing Tech University, Nanjing, China;
Department of Civil and Environmental Engineering, National University of Singapore, 117576, Singapore
 

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