Experimental Investigation of Thermal Bowing for Concrete Insulated Wall Panels

Abstract

Precast concrete insulated wall panels (IWP) are thermally and structurally efficient systems commonly used in construction. Although their flexural performance has been studied extensively, there are limited studies on thermal bowing in IWP. Bowing causes unwanted deflections, stresses on the panel and connections, and gaps in structures on their corners (i.e. ‘fishmouth effect’). Due to the lack of experimental results, designers and modelers rely on prior experience when considering thermal bowing. Four 6.1 m long IWP with 75 mm wythes and insulation were constructed. Each IWP has different diameters of Glass Fibre Reinforced Polymer (GFRP) shear connectors (9.5 to 16 mm) spaced at 610 mm in an X-arrangement. The shear connection stiffness was determined using push-through tests. Push-through results showed non-linear behaviour and quicker loss of stiffness as connector size increased. Based on push-through results it is more efficient to use smaller connectors (#3 bar) than larger connectors, as smaller (9.5 mm) connectors were capable of carrying 84% more stress than the 16 mm connectors. The resulting load-slip curves and stiffness of connectors to be used in understanding the thermal testing were also presented. Furthermore, a thermal enclosure was fabricated to cause thermal bowing in IWP using connectors from the push-through test. Bowing was induced by heating the wythe inside the enclosure to temperature differentials over 20°C. In terms of displacement per °C, the results showed end slip behaviour decreased 9.2% with the use of higher sized connectors compared to lower sized connectors; however, increased 16% for bowing effect in higher sized connectors compared to lower sized connectors. This shows the stiffer connector’s ability to translate resistance to end slip, into forces that create bowing. The panel with stiffest connectors showed thermal loads of 182 kN (temperature differential of 20°C) caused loss of stiffness, cracking, and permanent deformation.