Structural Performance of Sandwich Concrete Walls including UHPC and GFRP Reinforcement under Bending and Axial Loads
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This thesis investigates the structural performance of two sandwich walls; one suited for precast applications while the other for cast-in-situ. The first is an insulated double wythe design using very thin (25 mm) ultra high performance concrete (UHPC) wythes with a layer of extruded polystyrene styrofoam (XPS) core and small diameter (4.2 mm) glass fibre-reinforced polymer (GFRP) bars for reinforcement and ties/connectors. The second wall utilizes GFRP flat plates stiffened by T-shape ribs, as stay-in-place (SIP) structural forms on either side, with a concrete fill in between. For the first wall type, thirteen 3000 x 600 x (100-200) mm panels were tested under out-of-plane bending (M) with and without axial loading (N) applied to one wythe to simulate both architectural and load-bearing walls. The study compared steel and PVA fibers in the UHPC, and examined GFRP reinforcement ratio in the wythes, insulation thickness, amount and configurations of GFRP connectors, and the level of axial load. The full moment – axial load interaction envelope was developed, including slenderness effects. Panels with GFRP reinforcement achieved 78% higher moment capacity than those with fibers only. As insulation thickness increased by a third, moment capacity increased by 2.4 times. The degree of composite action in panels with transverse ties was 5-15% while that of panels with diagonal ties was 32-78%. The design met serviceability requirements at the highest wind pressure based on the 50-year return period in Canada. Failure was generally governed by fracture of shear connectors. For the second wall type, six 3000 x 616 x (150-200) mm panels were tested under out-of-plane moment, with and without axial load to establish the moment – axial load envelope, including slenderness effect. Surface treatment of GFRP forms using epoxy-bonded gravel resulted in full composite action, reaching 30% higher moment capacity compared to untreated panels. Concrete shear cracking occurred and propagated into horizontal delamination above the GFRP ribs. A simplified design approach is presented. Additionally, nine (1060-1945) x 170 x 245 mm panels were tested under in-plane moment, including spliced GFRP panels. Adhesively spliced beams reached 92-96% the moment capacity of their unspliced counterparts. Mechanically fastened specimens reached 86-92% of the moment depending on fastener spacing compared to unspliced specimens. The in-plane moment capacity for a section with a 7.6% GFRP reinforcement ratio was found to be the same as a conventional steel-reinforced section of the same size with a 3% ratio.
URI for this recordhttp://hdl.handle.net/1974/28725
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