Improving Composite Action in Circular CFST Columns Using Internal Spiral Plates

Sandeep TN; Job Thomas

doi:10.56748/ejse.26990

Authors

Sandeep TN Cochin university of Science and Technology, Kerala https://orcid.org/0000-0003-2200-9412
Job Thomas Cochin University of Science and Technology https://orcid.org/0000-0002-3832-4073

DOI:

https://doi.org/10.56748/ejse.26990

Keywords:

Concrete filled steel tube column, finite element analysis, confined CFST column, spiral plate stiffener

Abstract

Numerous confinement techniques have been proposed to enhance the strength and ductility of circular concrete-filled steel tube (CFST) columns. This study introduces an innovative confinement method for short circular CFST columns incorporating internal spiral plate stiffeners. The rectangular spiral plates are attached to the inner surface of the steel tube such that their flat faces remain in direct contact with the tube wall. This configuration minimizes obstruction to concrete flow and ensures proper compaction without void formation during casting. The spiral plates were connected to the steel tube using intermittent external fillet welding and tested under axial compression to evaluate their influence on load-carrying capacity and deformation behavior. A detailed finite element (FE) model was developed to complement the experimental program and to investigate the effects of key parameters, including spiral pitch, plate width, and weld spacing, on axial performance. The results demonstrate that incorporating spiral plate stiffeners increases the ultimate strength by an average of 16% compared to conventional CFST columns. Strength enhancement ranged from 5% to 55% as the spiral pitch decreased from 150 mm to 25 mm, while reducing weld spacing from 180° to 30° improved strength by 6–10%. A normalized spiral pitch (p/D) ≤ 0.5 provided effective confinement, resulting in stable post-peak behavior and mitigation of local buckling. Increasing the spiral plate width up to 40 mm enhanced axial strength by approximately 22%, highlighting its contribution to improved load resistance. Furthermore, the spiral plates were effectively delayed and uniformly distributed local bulging along the column height.

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