Hybrid Members Employing FRP Skin Reinforcement for Beams and Cladding Wall Applications

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Shawkat, Waleed
Sandwich Panel , CFT
This thesis explores two hybrid systems employing a core material reinforced by an external skin, namely, cladding walls composed of polyurethane foam core sandwiched between fibre-reinforced polymer (FRP) skins, and beams composed of concrete-filled FRP or steel tubes. The walls were studied in two phases. In phase I, the polyurethane foam core was injected between two carbon-FRP (CFRP) skins. Ten panels were tested to investigate their structural performance and failure modes. Test parameters included quality control in terms of reproducibility of test results, moment-shear ratio, and the orientation of an architectural masonry-like coating. The study showed that design is governed by stiffness and not strength and that the CFRP was underutilized. Also, quality control was shown to be poor for this method of fabrication. As such, in phase II, ten panels were fabricated by laminating glass-FRP (GFRP) skins to prefabricated polyurethane foam blocks. Similar flexural testing was carried out to investigate two different densities of foam, and moment-shear ratio. The study showed evidence of high quality control and that the density of the foam core significantly affected flexural capacity and stiffness. Rectangular concrete-filled tubes (CFTs), with either steel or pultruded GFRP tubes were fabricated and tested as beams in three-point bending, at different shear span-to-depth (a/d) ratios of 1 to 5 to examine crack patterns, strength and failure modes. It was shown that the critical (a/d) ratio, at which moment capacity drops, is between 4 and 5 for CFTs with GFRP tubes and between 1 and 2 for CFTs with steel tubes. It was also shown that ductility is drastically reduced at (a/d) ratios below 3 for steel tubes. Crack pattern and size were highly dependent on the magnitude of slip between the concrete and tube. A major full depth flexural crack developed in all CFTs with GFRP tubes. However, when internal steel rebar was added, major diagonal cracks were formed in addition to fine flexural cracks. In CFTs with steel tubes, fine flexural cracks developed, except at a/d = 1, where fine diagonal cracks were predominant. A strut-and-tie model was developed and provided reasonable agreement with test results.
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