Structural and Steady-State Thermal Experimental Investigations of an Insulated Sandwich Panel
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Concrete-Insulation-Concrete Sandwich Panels with Glass Fibre Reinforced Polymer (GFRP) shear connectors can be a solution to increasing energy efficiency in building envelopes, while also providing many architectural, structural, and economic benefits for building designs. This study consists of extensive experimental investigation of the shear and thermal properties of a unique sandwich panel design, incorporating GFRP shear connectors and a concrete “stud” system. The goal of this study is to expand upon the knowledge of alternative connectors’ effect on structural and thermal properties of sandwich panels, and to develop a thermally, structurally, and economically efficient panel. In the structural phase fifty 254x254x900 mm specimens representing segments of the precast sandwich wall, comprising two concrete wythes and a concrete stud surrounded by insulation foam, were tested in a double shear configuration. Three types of GFRP connectors produced from available sand-coated and threaded rods were tested and compared to conventional steel and polymeric connectors. GFRP connector diameters varied from 6 to 13 mm, and spacing varied from 80 to 300 mm. Both circular and rectangular cross-sections were examined, along with various end treatments to compare with simple straight embedment. The shear strength of GFRP connectors ranged from 60 to 112 MPa, significantly higher than polymeric connectors but lower than steel connectors. As the connectors bridged a small gap of insulation between the concrete wythe and stud, their shear strength was lower than manufacturer reported values due to the presence of some bending. Varying the size, spacing, cross-section shape or end treatment of connectors had insignificant effect on their strength. The connectors failed by longitudinal delamination then transverse shear, but did not pull out of the concrete wythe. Adhesion bond between concrete and insulation was significant and contributed about 28% of resistance, but was too variable for use in design. In the thermal testing phase, ten 254x1550x2400 full-scale specimens were tested in a purpose-built hot box apparatus under steady-state conditions. GFRP connectors showed minimal thermal bridging regardless of cross-section area or spacing, while steel connectors demonstrated significant thermal bridging in recorded temperatures despite a smaller cross-section area, and were clearly visible in thermal imaging.