Behaviour of Circular Columns Strengthened by Glass Fibre Reinforced Polymer Wrapping System

Behaviour of Circular Columns Strengthened by Glass Fibre Reinforced Polymer Wrapping System

The development of the thin and flexible prefabricated glass fibre reinforced polymer (GFRP) composites has been recognised as an innovative wrapping material that requires the inclusion of infills to complete its retrofitting system. However, the actual performance of this system still needs to be explored, and its structural contribution to axial and flexural behaviour of columns is yet to be determined. This study focused on the impact of the GFRP wrapping system on the axial and flexural behaviour of reinforced concrete (RC) and timber columns. The study included development of three-dimensional (3D) finite element (FE) and theoretical models to obtain an improved understanding about the performance of the investigated columns.

Firstly, the effectiveness of the thin GFRP wrapping and its contribution to the axial compressive behaviour of concrete, grout, and epoxy infill materials was explored, and the compressive behaviour of GFRP-wrapped infill materials was numerically elaborated using FE modelling. The experimental results showed that the properties of the infill material have a significant impact on the confinement effect of the wrapping system. The FE investigations that considered concrete damaged plasticity model for simulating the behaviour of materials, had an excellent agreement with the experimental results in predicting the overall compressive behaviour of the various infill materials.

Secondly, the flexural behaviour of circular RC columns strengthened by a GFRP wrapping system was explored experimentally, numerically and theoretically. The adopted system was found to improve the flexural capacity of columns by up to 250%. The assumption of a non-perfect bond between constituent materials in modelling the wrapped column infilled with grout, was shown to better correlate with their corresponding results, indicating inadequate bond performance.

Thirdly, the effect of rehabilitation with the thin GFRP composites was examined on the axial performance of short timber columns. Experimental work was conducted on undamaged and damaged short timber columns with three levels of splitting. Numerical and analytical investigations were established to evaluate the performance of the studied samples. The experimental results showed that the GFRP wrapping system had a significant impact on the axial performance of columns, with samples had epoxy infill contributing the most to the yield and peak strengthening ratios by 238% and 214%, respectively. The results of the numerical and analytical investigations were in good agreement with the experimental results.

Furthermore, the contribution of the GFRP wrapping system to the flexural capacity of circular timber columns was evaluated. The use of carbon fibre reinforced polymer (CFRP) straps within the epoxy infill was examined. Finite element modelling (FEM) and theoretical analyses were performed, and the results were compared with experimental results. The outcome of study demonstrated that the use of GFRP wrapping system with epoxy infill and bonded CFRP straps outperformed the investigated columns in terms of flexural strength and energy absorption due to the high elastic modulus and tensile strength of CFRP straps in contrast with other constituent materials. The theoretical study revealed that the estimation of tension failure in timber yielded results that corresponded more closely to experimental and FEM results.

Finally, FE study was performed using ABAQUS software package to provide a better understanding of the influence of various design parameters on the axial and flexural behaviour of GFRP-wrapped RC columns. The results of the FE investigations showed that including epoxy infill within the GFRP wrapping system improves the axial and flexural load capacities and failure modes of the columns more significantly when compared to grout infill. For columns under compression, the smaller the column size, the higher the impact of GFRP confinement on axial capacity and stiffness. For columns under flexure, the GFRP circumferential repair with an epoxy infill was more effective than grout infills in improving the flexural capacity of RC columns.

This study provided a thorough assessment of the performance of GFRP wrapping system and its influence on the axial and flexural behaviour of RC and timber columns. In addition, a deep understanding of the impact of various design parameters on the axial and flexural behaviour of RC columns was presented. Overall, the investigated GFRP wrapping system was found to be a suitable strengthening approach for circular structural columns that can enhance their performance.

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