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Modeling and comparative analysis of sustainable cotton rope confinement: Full vs. STrip wrapping for enhanced concrete strength and ductility
(2025-07-01)
Saingam, Panumas
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Gadagamma, Chaitanya Krishna
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Hussain, Qudeer
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Hlaing, Hnin Hnin
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Suwannatrai, Rawirot
The rise of natural FRPs as ecological alternatives to synthetic ones has highlighted the need for studies on partial confinement using cotton ropes, which offer cost-effective, low-carbon solutions with high rupture strain. Unlike full confinement, partial confinement through cotton rope strips can efficiently strengthen deteriorated concrete sections with reduced material usage. Despite possessing several advantages, the partial confinement by cotton on concrete has not been investigated. This study addresses the gap by investigating the performance of cotton rope strips and developing analytical models to predict their structural impact. This study tested cylindrical concrete specimens of two strengths, strengthened with cotton rope in either complete wrapping (Group 1) or strip wrapping (Group 2). Each group was further divided by concrete strength and included one unstrengthened specimen, and three strengthened with one, two, or three layers of cotton rope. Experimental results revealed that cotton rope wraps effectively confined the concrete, enhancing load-bearing capacity and improving ultimate compressive strength by 9.97–152.10 % and ultimate strain by 188.00 % to 1488.89 %. The compressive stress vs. strain behavior exhibited an initial stiff elastic ascent followed by a parabolic transition. The second branch of the response, either ascending or descending, was significantly improved with an increased confinement ratio. Type-I failure was characterized by an ascending second branch in the compressive stress vs. strain curve, while Type-II failure exhibited a descending second branch. Four specimens demonstrated Type-I failure (L-2F, L-3F, H-3F, and L-3S), predominantly in full configurations and with lower unconfined compressive strength. The modulus of the second branch improved with an increased confinement ratio, transitioning from Type-II to Type-I failure near a ratio of approximately 0.50. Regression analysis provided equations of various key points along the compressive response with R² values greater than 0.90, highlighting a strong dependence on the confinement ratio. The Popovics model effectively predicted the first part of the compressive response, with predicted curves closely matching experimental results.
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Enhancing compressive behavior of concrete with novel low-cost hybrid passive confinement including large rupture strain cotton ropes: Experimental findings and a design-oriented model
(2024-12-01)
Saingam, Panumas
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Hussain, Qudeer
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Ejaz, Ali
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Nawaz, Adnan
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Joklad, Panuwat
Recent research have highlighted the potential of hybrid confinement, combining high tensile strength fiber-reinforced polymers with large rupture strain confinement. This study presents experimental findings on 64 cylindrical and square-shaped specimens tested under axial compression, introducing a novel hybrid confinement method utilizing low-cost fiberglass chopped strand mat sheets and cotton ropes (COFS confinement). The experimental and analytical results yielded several key conclusions. Firstly, circular specimens exhibited significant peak strength increases in various subgroups, with enhancements ranging from 97.5 % to 285.5 %, and ultimate strain improvements ranging from 588.6 % to 1650.0 %. Similarly, square specimens under COFS confinement also demonstrated notable enhancements in ultimate strength and strain, with increases up to 244.7 % and 1083.0 %, respectively, particularly evident with higher levels of confinement. The influence of cross-sectional shape on compressive strength, strain, and energy dissipation was noted, with COFS confinement notably improving these factors for circular sections. Additionally, the study found that as the unconfined compressive strength increased, the enhancement in compressive strength, ultimate strain, and energy dissipation decreased. Moreover, the confinement ratio positively affected axial behavior improvement, with a proportional enhancement observed. However, the efficacy of the confinement ratio was influenced by cross-section type and plain concrete strength, emphasizing the need for considering these factors in COFS-based confinement design. Lastly, an analytical design-oriented model proposed for approximating stress vs. strain curves of COFS-confined concrete showed close agreement with experimental results, providing valuable insights for future design considerations.
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Large rupture strain cotton ropes hybridized with affordable fiberglass chopped strand mat sheets for enhanced compressive behavior of reinforced concrete columns
(2024-11-15)
Saingam, Panumas
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Gadagamma, Chaitanya Krishna
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Hussain, Qudeer
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Ejaz, Ali
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Hlaing, Hnin Hnin
The hybrid confinement system combines various fiber types within a single matrix, allowing for the adjustment of volumetric ratios to optimize confinement performance. Synthetic FRPs are more expensive and have a higher carbon footprint due to significant CO<inf>2</inf> emissions during production. In response, this study presents an innovative hybrid confinement approach using two natural materials: cotton ropes and FSMS (CFS) to improve concrete strength and ductility. Specimens, standardized at 300 mm height and 150 mm diameter with longitudinal steel bars and stirrups, were divided into two groups based on CFS configurations. The stress-strain response of CFS-confined concrete displayed distinctive behavior: an initial parabolic phase leading to peak compressive stress (ultimate strength), followed by a linearly degrading phase. Across all subgroups, CFS confinement significantly enhanced ultimate strength and corresponding compressive strains, with Subgroup 2A achieving the highest improvements of 246 % in ultimate strength and 1477 % in strain. Moreover, the ductility gain was reported as high as 20 for CFS-confined concrete. A non-proportional enhancement in the compressive behavior was observed with the increase in confinement ratio. Predictive models were developed for the idealized two-branch response of CFS-confined concrete, encompassing expressions based on nonlinear regression for ultimate strength, corresponding strain, ultimate strain, and elastic modulus. Two existing models were modified to trach each branch of the response. Integrating these two adjusted models closely replicated the experimental compressive curves.

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