Thermal-Structural Analysis and Thermal Bowing of Double Wythe UHPC Insulated Walls

Abstract

Ultra-high performance concrete (UHPC) was recently introduced to the precast concrete sandwich panel (CSP) industry, resulting in significantly thinner and lighter panels than those with conventional concrete. As exterior walls, they are expected to endure a wide range of seasonal temperatures, causing thermal bowing. A robust thermal-structural coupled finite element (FE) model, capable of modeling the partial composite action, was developed for the UHPC CSPs to assess their thermal bowing behavior. Three CSP designs, differing mainly in configuration and quantity of shear connectors, have been studied. Thermal loading was introduced by subjecting one surface to a constant room temperature, and the other to a variable temperature range of -50 °C to +60 °C. The model predictions were validated using panels tested under thermal and structural loading. The analysis revealed that panel deflections increased with the degree of composite action but satisfied serviceability requirements for the full range of temperatures. Cracking of the UHPC wythe occurred when the temperature differential (ΔT) between the two surfaces was equal to or less than -7 °C. The maximum tensile stress in the connector was less than 12% of its tensile strength, and occurred in the first connector from the panel end, which is consistent with the maximum relative slip between wythes.