Master of Engineering (Research)
School of Civil, Mining and Environmental Engineering
Le, Tan Duy, Performance of hollow core square reinforced concrete members wrapped with CFRP with different fiber orientations under static loading, Master of Engineering (Research) thesis, School of Civil, Mining and Environmental Engineering, University of Wollongong, 2013. http://ro.uow.edu.au/theses/3934
The present study deals with strengthening hollow core reinforced concrete (RC) columns and beams using external wrapping of Carbon fiber reinforced polymer (CFRP). The effects of fiber orientation of CFRP sheets on the axial load capacity of the columns and the shear capacity of the beams are the main parameters investigated from this study.
Hollow members have been widely used in structures due to their evident advantages when compared to the solid members, such as significantly reducing the dead load of the superstructures, leading to the decrease of foundation dimensions while maintaining the strength and stiffness of the structure. As a result, the cost of construction is reduced. However, strengthening hollow columns and beams with FRP has not been well investigated. Therefore, studying the use of FRP for strengthening hollow core columns and beams is necessary.
Sixteen specimens were designed and tested under different loading conditions in this study. These specimens were divided into two series. The first series consisting of twelve specimens and were tested as columns under concentric axial load, 25 mm and 50 mm eccentricity to investigate the effect of fiber orientation on the performance of the hollow core FRP-confined columns. The second series which included four specimens were tested as beams under four-point loading to study the improvement in shear capacity. All the specimens had square cross-section with 200 mm side dimension, 800 mm height and an 80 x 80 hole at their centers. The specimens were wrapped with CFRP sheets in different combinations of fiber orientations of 0°, 45°, and 90°.
For column specimens, test results showed that all wrapping configurations increased both the strength and ductility of hollow core square RC columns. The increase in ductility was significant for all specimens, especially for the specimens exclusively wrapped with hoop CFRP layers. Meanwhile, the increase in the compressive strength was marginal for all specimens (9% to 25% increases as compared with the control column). The fiber orientation influencing the gain in strength and ductility of the columns varies between different loading conditions. When the eccentricity was small, the use of CFRP layers in the hoop direction was shown to be the most effective wrapping method to enhance both the strength and ductility of the columns. For columns loaded under a large eccentricity, the combinations of the hoop layers with the vertical or diagonal layers outperformed the combination of the hoop CFRP layers only in terms of strength enhancement. In contrast, the ductility of the columns with CFRP in the hoop direction was greater than that of the columns wrapped with the other combinations.
These wrapping configurations were shown to be much more efficient for the case of shear strengthening than for axial load strengthening. All wrapping configurations substantially increased the shear strength of the hollow RC beams (97% to 219% increases as compared with the control beam). The change in the fiber direction strongly affected the gain in the shear capacity and failure modes of the beam specimens. The combination of vertical CFRP layers to the longitudinal axis of the beam changed the failure mode of the beam to flexural failure, which was more ductile than shear failure. The combination of two diagonal and one vertical CFRP sheets to the longitudinal axis of the beam considerably increase the shear strength and deflection capacity of the beam.