International Journal of Civil and Structural Engineering Research ISSN 2348-7607 (Online) Vol. 10, Issue 2, pp: (10-33), Month: October 2022 - March 2023, Available at: www.researchpublish.com
Performance and strengthening of the circular R.C. Columns with high slenderness ratios using GFRP External Wrapping Nehal M. Ayash 1, Abeer Fathy 2, Ata El-kareim Shoeib3 1
2
Assistant professor Civil Engineering Department, Faculty of Engineering at Mataria, Helwan University, Cairo 11718, Egypt
M.Sc. student Civil Engineering Department, Faculty of Engineering at Mataria, Helwan University, Cairo 11718, Egypt 3
Professor of Reinforced concrete structures, Civil Engineering Department, Faculty of Engineering at Mataria, Helwan University, Cairo 11718, Egypt DOI: https://doi.org/10.5281/zenodo.7330504
Published Date: 17-November-2022
Abstract: The research investigated the behavior of reinforced concrete (RC) columns which have high slenderness ratios, and this strengthens with GFRP wrapping laminate. Twelve RC columns having a circular cross-section with various slenderness ratios (H/D) 16, 18, 20, and 22 were tested experimentally under concentric axial load. The first group of columns was non-strengthened as control. Secondly, the fully strengthened with GFRP wrapping laminates in the hoop direction and thirdly, the partially strengthened with GFRP wrapping laminates in the hoop direction were tested. Then the numerical models were developed and validated with the experimental results. The numerically developed model was implemented to demonstrate the effect of changing the orientation of the GFRP laminates, in addition, the effect of applied the eccentric axial load on the capacity of the strengthened slender columns were explored. Lastly, the experimental results for unconfined and FRP-confined columns are compared with ECP and ACI codes provisions. It can be concluded that increasing the slenderness ratio of columns causes a reduction in the ultimate axial load, axial deformation arising from decreasing the column stiffness but increasing the lateral deformation. Fully wrapped enhanced the lateral deformation of slender columns by reducing them by 0.8 to 0.55 when compared to partially wrapped as the slenderness ratio increased from 16 to 22. The column capacity predicted by ECP is more conservative than ACI for unconfined and confined slender columns. GFRP hoop strengthening barely increased the resistance for slender columns, while GFRP strengthening in the longitudinal direction contributes to their capacities. Keywords: circular columns; GFRP; Slenderness ratio; ductility index; initial load eccentricity.
I. INTRODUCTION The usage of slender columns is widespread nowadays due to the rapid increase in the number of high-rise buildings resulting from the architectural development of the age. The slenderness ratio is one of the crucial parameters that affect the behavior of slender RC columns. The slenderness ratio can be defined as the ratio of the column effective length to the least of the radius of gyration of the cross-section. In addition, it can be defined by the ratio of effective length to the smallest dimension of the cross-section. Columns with higher slenderness ratios are vulnerable to instability buckling failure resulting from the secondary moment effect. This effect led to a significant reduction in their ultimate resistance compared to that of short columns. ACI-318 and ECP-203 state limits for slender columns, the slenderness ratio (KH/r) is not exceeded 40 for ACI-318 and is not exceeded 70 for ECP-203, where H is unsupported column height, r is the crosssection radius of gyration and K is constant that reflect the column end conditions. Increasing the resistance of the slender columns is required strengthening to withstand the excessive loads. One solution for strengthening elements is using fiber-reinforced polymer wrapping (FRP) for improving columns confinement.
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