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Steel and Composite Structures
  Volume 19, Number 1, July 2015 , pages 21-41

Push-out tests and bond strength of rectangular CFST columns
Xiushu Qu, Zhihua Chen, David A. Nethercot, Leroy Gardner and Marios Theofanous

    Push-out tests have been conducted on 18 rectangular concrete-filled steel tubular (CFST) columns with the aim of studying the bond behaviour between the steel tube and the concrete infill. The obtained load-slip response and the distribution of the interface bond stress along the member length and around the cross-section for various load levels, as derived from measured axial strain gradients in the steel tube, are reported. Concrete compressive strength, interface length, cross-sectional dimensions and different interface conditions were varied to assess their effect on the ultimate bond stress. The test results indicate that lubricating the steel-concrete interface always had a significant adverse effect on the interface bond strength. Among the other variables considered, concrete compressive strength and cross-section size were found to have a pronounced effect on the bond strength of non-lubricated specimens for the range of cross-section geometries considered, which is not reflected in the European structural design code for composite structures, EN 1994-1-1 (2004). Finally, based on nonlinear regression of the test data generated in the present study, supplemented by additional data obtained from the literature, an empirical equation has been proposed for predicting the average ultimate bond strength for SHS and RHS filled with normal strength concrete.
Key Words
    composite construction; concrete filled steel tubes; interface bond strength; interface condition; push-out test; slip
(1) Xiushu Qu:
School of Civil and Transportation Engineering, Beijing University of Civil Engineering and Architecture, Beijing, 100044, PR China;
(2) Xiushu Qu, Zhihua Chen:
School of Civil Engineering, Tianjin University, Tianjin, 300072, PR China;
(3) David A. Nethercot, Leroy Gardner:
Department of Civil and Environmental Engineering, South Kensington Campus, Imperial College London, SW7 2AZ, UK;
(4) Marios Theofanous:
School of Civil Engineering, University of Birmingham, Edgbaston, B15 2TT, UK.

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