Authors : S. K. Katariya; Amit Rautela; Pankaj Prasad

Volume/Issue : Volume 10 - 2025, Issue 11 - November

Google Scholar : https://tinyurl.com/mwpv63yu

Scribd : https://tinyurl.com/snrnuv5k

DOI : https://doi.org/10.38124/ijisrt/25nov1123

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Abstract : This study presents a comprehensive nonlinear constitutive model for the in-filled concrete of square Concrete- Filled Steel Tube (CFST) columns, accounting for the confinement effects provided by the steel tube. Due to the non-uniform confinement in square sections particularly reduced effectiveness in flat regions compared to corners—the behaviour of the core concrete differs significantly from that observed in circular CFST columns. To capture this response, an effective lateral confining pressure model is formulated, incorporating tube thickness, yield strength, and confinement efficiency. The confined concrete strength and strain capacity are derived using an enhanced Mander-type relationship, and a continuous nonlinear stress–strain equation is proposed to represent both the ascending and descending branches of the concrete response. The model enables the generation of complete constitutive curves suitable finding the axial capacity of square CFST columns. Validation against experimental data from the literature demonstrates that the proposed formulation predicts peak stress and overall axial behaviour of square CFST columns. The model provides a reliable analytical tool for structural designers and researchers for simulating the nonlinear compression behaviour of concrete infill in square CFST systems.

Keywords : CFST Column, Axial Compression, Confinement, Nonlinear Behaviour.

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