الفهرس 
Chapter (1): IntroductionOnly 14 pages are availabe for public view
 |  | from | 146 |  |  |
| | | from | 146 | | |
Abstract
A comprehensive investigation into the behaviour of BFRP-strengthened RC columns (short and long) was carried out through intensive experimental and numerical study. Nineteen RC column specimens were subjected to experimental investigation. These column specimens were categorized into two groups based on the type of load they were subjected to. The first group consisted of eccentric column specimens with dimensions of 200×200×1500 mm, while the second group consisted of axial column specimens with varying cross-sectional shapes. To provide a comprehensive assessment about the behavior of columns under this technology, various parameters were investigated such as the strengthening materials (BFRP-W, BFRP-B, and CFRP-W, the strengthening schemes (fully or partially wrapping, the number and direction of layers), and the cross-sectional shapes (square, rectangular, and circular). The effects of these parameters were investigated for ultimate load capacity, vertical displacement, lateral displacement, vertical strain, and failure mode and crack pattern. The numerical study is composed of eighteen columns, with the specimens separated into two groups based on the effect of displacement and the aspect ratio. To simulate the experimental work, the bond between the concrete and BFRP is fully bonded in the predicted FE model.
6.2 Conclusion
6.2.1 Experimental investigation
The purpose of this investigation was to demonstrate the efficacy of using BFRP to reinforce RC columns. After analysing the experimental findings, the following conclusions were drawn.
1) Strengthening RC columns with BFRP significantly enhances their behavior by increasing energy absorption, exhibiting up to 500% improvement compared to unconfined columns, while also effectively promoting crack propagation.
2) In the case of eccentric loads, increasing the number of BFRP-W layers can boost the maximum load capacity. For instance, compared to a control column, adding one horizontal BFRP layer, two horizontal BFRP layers, or one horizontal and one vertical BFRP layer can increase the bearing capacity by approximately 19.89%, 36.44%, and 31.63%, respectively.
3) The combination of BFRP and CFRP materials in the confinement system contributes to improved absorbed energy and crack control. The hybrid system’s ability to effectively manage cracking helps maintain the column’s integrity under varying loads and prevents brittle failure modes.
4) The use of BFRP confinement in elliptical columns, along with the implementation of 20 mm radius corners, results in a remarkable increase in load-bearing capacity. The increase in load-bearing capacity signifies that the BFRP confinement and corner design contribute to a more efficient utilization of the column’s cross-sectional area and material properties, resulting in enhanced structural performance.
5) The combination of NSM BFRP-B and externally bonded BFRP-W creates a synergistic effect in confining the concrete core of the column. NSM reinforcement provides effective confinement closer to the surface, while externally bonded wraps enhance confinement across the entire cross-section. This dual approach improves the column’s ability to withstand axial loads by reducing lateral expansion.
6.2.2 Analytical investigation
1) For columns with single layer strengthening, all the equations from different codes provide reasonable failure stress results, while other authors underestimate them by a minor value. The ratio of theoretical strength to experimental stress ranges from 0.77 to 0.99.
2) While for columns strengthening with a single layer and BFRP bars, all equations underestimate by major value the failure stresses, of which the ratio of theoretical strength to experimental stress ranges from 0.66 to 0.80. In these models, the effect of BFRP bars were not directly considered in the calculation.
6.2.3 Theoretical investigation
1. The ANSYS-based FE model developed in this study was found to accurately simulate the BFRP specimens and provide reliable predictions that matched the experimental results. The validated model was subsequently used to explore a wider range of parameters.
2. Specimens with large eccentricity experience significant bending moments that induce tensile stresses on one side and compressive stresses on the other. By adding longitudinal BFRP layer on the tensile side, the confinement effect becomes more pronounced. This helps restrain the expansion of concrete and prevents the development of wide cracks, ultimately increasing the flexural capacity of the specimen.
3. Columns with different aspect ratios experience varying stress distributions and deformation patterns. The confinement effect becomes more pronounced in columns with a higher cross-section ratio, as the transverse expansion of the concrete is restricted more effectively. This has implications for the overall strength and ductility of the column.