74 PCI Journal | January–February 2020 ■ Five precast concrete sandwich panels with different structural configurations were tested under ambi- ent laboratory conditions to determine the panels’ shrinkage strain behavior. ■ The results of the experimental testing were used to develop strain profiles for finite element analysis to investigate the effect of key parameters on the early-age behavior of the precast concrete sandwich panels. ■ The results of the study show that using a bilinear shrinkage profile for each concrete layer in the anal- ysis accurately predicts the shrinkage strains and that early-age cracking can occur in precast concrete sandwich panels that are not properly cured or that have a high reinforcement ratio. P recast concrete sandwich panels (PCSPs) are becoming popular because of their advantages in terms of rapid speed of construction, superior energy conservation, and flexible and diverse aesthetic options. 1,2 PCSPs are widely used as structural members in residential buildings, hospitals, industrial warehouses, and schools. 3 Traditional noncomposite PCSPs are commonly used and usually comprise one thick reinforced concrete layer and one thin layer of concrete cladding connected using mechanical anchors. Composite PCSPs that use shear connectors in the form of diagonal steel or fiber reinforced polymer (FRP) re- inforcing bars to connect the two reinforced concrete layers are becoming popular due to their improved shear trans- fer mechanism and material savings. 4 In composite PCSP applications, the two reinforced concrete layers are the same thickness, and the overall thickness of the panel is about ½ to 2 ∕ 3 of a comparable noncomposite panel while still offering relatively similar structural and thermal insulation prop- erties. 3 No official standards have been established to date for designing PCSPs, and relatively little research has been reported on their early-age structural behavior. 5 Because PCSPs are normally designed to ensure crack-free perfor- mance, a careful look at all potential causes of cracking is needed, especially at the panels’ early age, while concrete is still immature with relatively low tensile strength. The most critical aspects of structural behavior of concrete at an early age are thermal deformation and shrinkage. Thermal deformation is mainly caused by heat dissipation (cooling) of concrete after casting, when the hydration Early-age shrinkage effects in precast concrete sandwich panels Qian Huang, Ehab Hamed, and R. Ian Gilbert PCI Journal (ISSN 0887-9672) V. 65, No. 1, January–February 2020. PCI Journal is published bimonthly by the Precast/Prestressed Concrete Institute, 200 W. Adams St., Suite 2100, Chicago, IL 60606. Copyright © 2020, Precast/Prestressed Concrete Institute. The Precast/Prestressed Concrete Institute is not responsible for statements made by authors of papers in PCI Journal. Original manuscripts and discussion on published papers are accepted on review in accordance with the Precast/Prestressed Concrete Institute’s peer-review process. No payment is offered.
Early-age shrinkage effects in precast concrete sandwich panels
Apr 28, 2023
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