Influence of Corner Rounding on the Axial Capacity of GFRP-Confined Square RC Columns: A Finite Element and Analytical Study

Author

Shivendra Kumar Pandey, Chandan Kumar


Abstract

 Many reinforced concrete (RC) columns in older buildings no longer meet present load demands because of material deterioration, changes in occupancy or design shortfalls. Wrapping such columns with glass fibre reinforced polymer (GFRP) sheets is a fast and lightweight way to raise their axial capacity, but in square sections the confining action is weakened at the corners. This study examines how rounding the corners of a square column before wrapping changes the gain in axial capacity. A 200 mm × 200 mm short RC column with M20 concrete and four 12 mm bars was analysed with and without a single layer of unidirectional E-glass GFRP, for sharp corners and for a corner radius of 25 mm. Three-dimensional nonlinear finite element (FE) models were built in ABAQUS using the concrete damaged plasticity model for concrete, embedded beam elements for steel and shell elements for the jacket. The FE results were compared with nominal capacities obtained from the CSA A23.3 column equation, using confined concrete strengths from the fib Bulletin 14 confinement-effectiveness approach. The FE model predicted an increase in axial capacity of 15.1% for the sharp-cornered column and 31.9% for the rounded column, against analytical increases of 12.6% and 22.6%. FE capacities were 3–11% higher than the analytical values. The jacketed rounded column also sustained 66% more axial deformation before the onset of nonlinearity. The jacket material cost was about ₹1,820 per m² of wrapped surface, and corner rounding roughly halved the cost per kN of capacity gained. Rounding the corners before wrapping is therefore recommended when square columns are strengthened with GFRP.



Keywords

GFRP jacketing, square RC column, corner radius, confinement, concrete damaged plasticity, finite element analysis, retrofitting



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References


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