Flexural Creep Effects on Permanent Wood Foundation Made of Structural Insulated Foam-Timber Panels

Abstract

The structural insulated panel (SIP) is an engineered composite product composed of an insulating foam core sandwiched to provide the insulation and rigidity, and two face-skin materials to provide durability and strength. SIPs can also be used as permanent wood foundation (PWF) for basements in low-rise residential construction to save in the energy cost. The maximum deflection equation specified in the Canadian Standard for Engineering Design of Wood, CAN/CSA-O86.09 specifies expressions for the effects of short-term bending deflection on the PWF timber stud walls. PWF is subjected to gravity loads associated with lateral soil pressure. To use the available combined bending and axial compression equation for PWF design, it was observed that the soil pressure would cause short-term and long-term flexural creep deflection of the wall that would decrease the wall capacity. Information on the long-term creep behaviour of SIPs under sustained triangular loading, simulating soil pressure, is as yet unavailable. As such, this paper presents a summary of flexural creep tests conducted to determine the increase in SIP deflection under soil pressure over a period of eight months. Using the experimental data, the available mathematical and mechanical creep models were evaluated to predict the flexural creep constant (K) of SIP foundation wall subjected to soil pressure over a service life up to 75 years. A flexural creep constant was then proposed to determine the long- term eccentricity of gravity loading in the available combined bending and axial compression equation for PWF design.