Elsevier

Journal of Constructional Steel Research

Volume 65, Issues 8–9, August–September 2009, Pages 1617-1630
Journal of Constructional Steel Research

Experiments on rectangular concrete-filled steel tubes loaded axially on a partially stressed cross-sectional area

https://doi.org/10.1016/j.jcsr.2009.04.004Get rights and content

Abstract

The present paper aims to experimentally investigate the behaviour of rectangular concrete-filled steel tubular (RCFST) stub columns loaded axially on a partially stressed cross-sectional area. A total of twenty-two specimens, including thirteen partially loaded composite specimens, six partially loaded plain concrete reference specimens and three corresponding fully loaded composite specimens, were tested under concentric loads. The main parameters varied in the tests are: (1) depth-to-width ratio of the rectangular sections: from 1.2 to 1.8; (2) partial compression area ratio (concrete cross-sectional area to partial compression area): from 1.44 to 17.42; (3) steel wall thickness of top endplate: from 0 mm to 12 mm; and (4) shape of the bearing plate for partial compression: rectangular and strip. The test results showed that, while being loaded on partial cross-sectional area, RCFST stub column had a favourable bearing capacity and ductility compared with the corresponding plain concrete specimens. Simplified formulae were used for the prediction of the ultimate strength of CFST stub columns loaded on partial cross-sectional area.

Introduction

Combining the advantages of both hollow structural steel (HSS) and concrete, rectangular concrete-filled steel tubes (RCFSTs) are being used widely in real civil engineering projects due to their excellent static and earthquake-resistant properties, such as high strength, high ductility and large energy absorption capacity.

When being used as a pier of bridge or a member for load introduction in high rise and multi-storey buildings, a RCFST column is often loaded on partial cross-sectional area. Fig. 1 illustrates a schematic view of RCFST columns loaded on partial cross-sectional area. Recently, the performance of partially loaded CFST has been the interests of structural engineers.

In the past, many studies had been conducted for RCFST columns to investigate the static and dynamic behaviours. Shakir-Khalil and Zeghiche [1] tested seven full-scale concrete-filled rolled steel rectangular columns about 3 m long. Shakir-Khalil and Mouli [2] further tested nine full-scale 3m-long and thirteen short concrete-filled rolled steel rectangular columns. Bradford [3] developed a procedure for predicting the strength of RCFST slender columns based on the intersection of the section strength envelope and the nonlinear loading line. Schneider [4] presented an experimental and analytical study on the behaviour of RCFST stub columns. Wang [5] tested eight concrete filled rectangular hollow steel section columns with end eccentricities producing moments other than single curvature bending. Han [6] experimentally studied the performance of RCFST stub columns and the tested bearing capacities were compared with the predictions of the available design specifications. Zhao et al. [7] described a series of tests on empty and void-filled rectangular hollow section (RHS) braces subjected to static and cyclic axial loading. Han et al. [8] performed the tests on RCFST columns under constant axial load and cyclically increasing flexural loading. A mechanics model was developed to predict the cyclic responses of such columns. Lue et al. [9] tested twenty-four RCFST columns with high-strength concrete and the compressive concrete strength varied from 29 MPa to 84 MPa.

Bergmann [10], Cai [11], Porsch and Hanswille [12] and Han et al. 13., 14., 15. experimentally investigated the behaviour of CFST stub columns with circular and square sections loaded on partial cross-sectional area. It was found that, due to the partially loaded effects, the behaviour of such composite columns was significantly different from those of the fully loaded members. Based on the experimental and theoretical studies, the simplified models to predict the bearing capacities of circular and square CFST columns loaded on partial cross-sectional area were provided by Han et al. [15] and Han [16]. A design method considering the effects of the partial loading and the confinement of the steel tube was also presented in EN 1994-1-1 [17] and a CIDECT report (Bergmann et al. [18]).

From the literature review above, it can be concluded that there are still lack of information on rectangular concrete-filled steel tubes loaded on partial cross-sectional area. This means a further study is needed in this area.

This paper is thus an attempt to study the behaviour of RCFST stub columns loaded on partial cross-sectional area. The main objectives of the paper are threefold: first, to present test results on RCFST stub columns loaded on partial cross-sectional area; second, to analyze the effects of several parameters, such as, shape of bearing plate, partial compression area ratio, endplate thickness and depth-to-width ratio, on the behaviour of partially loaded RCFST specimens; and third, to predict the ultimate strength of CFST stub columns loaded on partial cross-sectional area by using a set of simplified formulae.

Section snippets

Experimental program

A total of 22 stub columns loaded on partial cross-sectional area, including 13 partially loaded RCFST specimens, 6 partially loaded plain concrete specimens and 3 fully loaded RCFST specimens, were tested. The main parameters varied in the tests include:

  • Depth-to-width ratio, η (=D/B; where, D and B are the outside depth and width of rectangular steel tube or plain concrete specimen respectively): from 1.2 to 1.8;

  • Partial compression area ratio, β (=Ac/Ap; where, Ac is the cross-sectional area

Strength index

For convenience of analysis, strength index (SI) for RCFST stub columns loaded on partial cross-sectional area is defined as: SI=Nue,pNue,f where, Nue,p and Nue,f are the measured ultimate strength of RCFSTs loaded on partial cross-sectional area and the corresponding fully loaded RCFSTs.

For plain concrete specimens loaded on partial cross-sectional area, SI is defined as: SI=Nue,pDBfc where, fc is the concrete compressive cylinder strength.

Fig. 11 illustrates the effects of the

Conclusions

We have attempted to study the behaviour of rectangular concrete-filled steel tubular (RCFST) stub columns loaded axially on partially stressed cross-sectional area. Based on the results of this study, the following conclusions can be drawn:

  • (1)

    Generally, the partially loaded RCFST stub columns exhibit a ductile performance. The partial compression effects can lead to the decrease of bearing capacities of the composite columns.

  • (2)

    While being loaded on partial cross-sectional area, the performance of

Acknowledgements

The work is financially supported by the Research Foundation of the Ministry of Railways and Tsinghua University (RFMOR & THU) (NO. J2008G011), the National Basic Research Program of China (973 Program) (Grant No. 2009CB623200) and the Program for Changjiang Scholars and Innovative Research Team in University (IRT00736). The financial support is highly appreciated.

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