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Steel and Composite Structures
  Volume 15, Number 6, December 2013 , pages 679-703

Fundamental behavior of CFT beam-columns under fire loading
Amit H. Varma, Sangdo Hong and Lisa Choe

    This paper presents experimental investigations of the fundamental behavior of concrete filled steel tube (CFT) beam-columns under fire loading. A total of thirteen specimens were tested to determine the axial force-moment-curvature-temperature behavior of CFT beam-columns. The experimental approach involved the use of: (a) innovative heating and control equipment to apply thermal loading and (b) digital image correlation with close-range photogrammetry to measure the deformations (e.g., curvature) of the heated region. Each specimen was sequentially subjected to: (i) constant axial loading; (ii) thermal loading in the expected plastic hinge region following the ASTM E119 temperature-time T-t curve; and (iii) monotonically increasing flexural loading. The effects of various parameters on the strength and stiffness of CFT beam-columns were evaluated. The parameters considered were the steel tube width, width-tothickness ratio, concrete strength, maximum surface temperature of the steel tube, and the axial load level on the composite CFT section. The experimental results provide knowledge of the fundamental behavior of composite CFT beam-columns, and can be used to calibrate analytical models or macro finite element models developed for predicting behavior of CFT members and frames under fire loading.
Key Words
    fire; columns; composite; experiments; temperature
(1) Amit H. Varma: School of Civil Engineering, Purdue University, 550 Stadium Mall Drive West Lafayette, Indiana 47907, USA;
(2) Sangdo Hong: Indiana Department of Transportation, West Lafayette, Indiana, USA;
(3) Lisa Choe: National Institute of Standards and Technology, Gaithersburg, Maryland, USA.

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