Doctor of Philosophy
School of Civil, Mining and Environmental Engineering
Yuan, Jiansong, Flexural behaviour of composite beams reinforced with GFRP I-section, Doctor of Philosophy thesis, School of Civil, Mining and Environmental Engineering, University of Wollongong, 2017. https://ro.uow.edu.au/theses1/151
Fibre reinforced polymer (FRP) pultruded profiles have found increasingly wide applications in recent years in civil engineering. Compared with the traditional FRP composites (e.g. FRP sheet or FRP bars), FRP pultruded profiles have some distinct advantages, such as the tailorability of the cross-section and ease of installation, which are desirable features in practical implementation. This thesis presents a research study on the application of FRP pultruded profiles in the composite beams, as well as the bond behaviour of the FRP pultruded profiles to concrete. The FRP pultruded profiles used in this study is the glass fibre reinforced polymer (GFRP) I-section.
In order to improve the ductility of the composite beams reinforced with FRP pultruded profiles, a new type of composite beams reinforced with FRP I-section and longitudinal tensile steel bars were proposed in this study. A total of five beam specimens were cast and tested by using four-point bending to investigate the flexural behaviour. The parameters included the location of the I-section and the type of the tensile bars. The test results show that the proposed composite beams possess a very ductile response due to the existence of the tensile steel bars, and the yield point of the composite beam was controlled by the tensile steel bars. Moreover, the ultimate load of the proposed composite beam was higher than the traditional reinforced concrete (RC) beam, and the ultimate load was governed by the encased I-section. The different location of the I-section in the cross-section had little effect on the flexural response of the beam specimens.
The relative slip between the concrete and the I-section was revealed in the flexural test, which affected the flexural response of the composite beams. Therefore, a push-out test was then conducted to investigate the bond behaviour between the I-section and the concrete. The specimens for the push-out test were in the form of a rectangular column with an I-section encased in concrete, and had the same cross-section dimensions as the beam specimens. The experimental results show that the ultimate bond strength could be improved by a longer bond length and sand coating. However, when stirrups were used, the ultimate bond strength was reduced. Then, a preliminary bond stress-slip model was proposed and the theoretical results were in good agreement with the experimental results.
The push-out test was followed by a direct shear test to determine the friction coefficient between the I-section and concrete. As a significant parameter of the interface, the friction coefficient cannot be determined by the push-out test, so a direct shear test was adopted in the study to obtain this parameter. The specimens were composed of a concrete block and a coupon of the I-section. The variables investigated included the type of the concrete, the coupons from a different part of the I-section and the compressive strength of the concrete. The test results show that the compressive strength of the concrete and the different component of the I-section had little effect on the friction coefficient, while the type of the concrete significantly affected the friction coefficient. The friction coefficient between the concrete and the I-section was between 0.5 and 0.6, and the adhesion stress was approximately 0.2 MPa.
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