۱- Introduction

۲- Simplified equation to predict the flexural strength of a CFST composite girder

۳- Experimental study

۴- Finite element analysis of the CFT composite girder for test specimens

۵- Parametric study and design consideration of the CFST composite girder

۶- Conclusion

References

Abstract

The flexural strength of the concrete-filled steel tube (CFST) composite girder was investigated in this study. Firstly, simple equations to evaluate the flexural strength of the CFST composite girder under both positive and negative bending moment were derived based on the plastic stress distribution method (PSDM). A series of tests was then conducted to verify the accuracy of the proposed equation, and to investigate the effect of internal shear connectors between the steel tube and concrete infill. Further, non-linear finite element analysis for each test specimen was performed to demonstrate the failure mechanism, and to set up the verified finite element analysis model. From the results, it was found that the proposed equations provided a reasonably conservative prediction of the flexural strength of the CFST composite girder under both positive and negative bending moment, and the effect of internal shear connectors between the steel tube and concrete infill on the flexural strength was negligible. A series of parametric studies was performed to investigate the effect of the D/t ratio, compressive strength of the concrete infill, and local buckling of the steel tube on the flexural strength of the CFST composite girder. Finally, some design considerations are noted based on the results of the parametric study.

Introduction

The concrete-filled steel tube (CFST) is a composite member that consists of steel tube and concrete infill. The major benefit of the CFST is that the concrete infill is confined by the tube resulting in a tri-axial state of compression that increases the strength and strain capacity of the concrete [1,2]. In particular, when subjected to cyclic axial or flexural loading conditions, the crushed concrete remains confined within the steel tube, providing high ductility and energy dissipation with delayed degradation of resistance [3,4]. Furthermore, the concrete infill restrains buckling deformation of the tube, and leads to an increase in buckling strength [5]. To take these benefits, CFSTs have been widely used as building columns and bridge piers, where the major loading is axial compression. Recently, the applications of the CFST have been extended to the superstructure of bridges. Chen and Wang [6] reported that CFST arch bridges have been built more than 200 since 1990 in China, and the CFST bridges become a good alternative to reinforced concrete bridges or steel bridges due to the structural advantages and artistic appearance of the CFST. Recently, CFSTs have also been used as parts of a girder to adopt the ability to provide strength, ductility, constructability and aesthetic [7–۱۱], and the CFST composite girder system was first proposed by Nakamura et al. [7]. Fig. 1 shows a typical CFST composite girder. The CFST composite girder consists of CFST and concrete slabs, and these are connected with mechanical shear connectors. By replacing the conventional Igirder with a CFST, the noise and vibration induced by cars or trains, which are the major disadvantages of a conventional steel I-girder bridge, can be reduced [9]. And it can also be expected that the local and global instability resistance of the bridge increases by using CFSTs. In the construction of the CFST composite bridge, steel tubes are produced at steel mill, thus little fabrication is required to make them bridge girders, and the steel tube serves as a formwork so that the labor associated with formwork can be reduced [6,9–۱۱]. Therefore, the CFST composite girder could be economical compared with conventional welded plate girders.