Flexural Response of Double-Wythe Insulated Ultra-High-Performance Concrete Panels with Low to Moderate Composite Action

■ The results of the flexural performance testing indicated that including flexural reinforcement in the wythes, increasing insulation thickness, or providing diagonal load paths with the shear connectors can significantly increase the ultimate capacity of the panels. A typical precast concrete insulated wall consists of the exterior concrete layer, referred to as the architectural or facade wythe; the interior concrete wythe, which could be load bearing; and a rigid insulation sandwiched between the wythes. Precast concrete panels are usually used as exterior walls, spanning from the foundation to the floor or from column to column in a structure. The overall thickness of the panel is determined based on the applied loads, the thermal performance requirements, and the expected level of composite action between concrete layers. The type of insulation and its thickness have a direct impact on the thermal performance of the panel. Rigid cellular foam is generally used as insulation, and the most common forms of this foam are extruded polystyrene (XPS) and expanded polystyrene. Concrete wythes are connected to each other using tie connectors. These connectors are generally installed perpendicular to the face of the wall and carry mostly axial forces during handling but provide very little composite action. To reach a higher level of composite action for enhanced structural performance, shear connectors are used to transfer the shear forces between concrete wythes. Traditional shear connectors, such as discrete concrete blocks or steel connectors, cause thermal bridging, significantly affecting the thermal performance of the wall. For example, using steel connectors with as low as an 0.08% reinforcement ratio can reduce the thermal performance of the panel by 38%.