Structural behaviour of insulated foam-timber panels under gravity and lateral loading

A Structural Insulated Panel (SIP) is a structural element of expanded polystyrene insulation (EPS) core sandwiched between two oriented-strand boards (OSB). This research proposes SIPs in low-rise residential construction (i.e. houses and low-residential building), replacing the traditional conventional joist floors and stud walls. This research investigates (i) developing expressions for flexural, compression, monotonic racking and cyclic lateral load capacities of SIPs as compared to the joist/stud wall construction. In this study, the proposed design of SIPs was based on (i) generally established theory for analysis, (ii) assessment of full-scale SIP panels by a loading tester, and (iii) computer modeling using the finite-element modeling. The research program included (i) testing SIP walls in axial compression and bending, (ii) racking and cyclic testing on SIP shear walls, (iii) development of finite-element computer models of the tested SIP panels and verifying those using experimental findings, (iv) correlation between experimental findings and design equations for strength and serviceability available in the literature and wood design Standards. Modification factors of these equations were developed to allow structural engineers to design SIP panels in residential construction more economically reliably. Experimental results showed that SIP panels are being “as good as” the conventional wood-framing of identical sizes, with respect to flexural, compressive, racking and cyclic loading. Also, results showed SIP walls have a greater ability to dissipate energy under racking and cyclic loading that the stud wall system. Therefore, SIP walls can be used so efficient in seismic zones. Based on cyclic lateral load test results, the values of ductility-related force modification factor (Rd) for stud wall, short SIP wall and long SIP wall were calculated as 8%, 22% and 14% lower than the NBCC required value for anchored wall (Rd = 3.0), respectively. In addition cyclic lateral load test results showed that the values of over-strength-related force modification factor (Ro) for stud wall, short SIP wall and long SIP wall were observed to be 17%, 20% and 14% higher than the recommended value of NBCC (Ro = 1.7) for anchored wall, respectively. So, it is concluded that the over-strength factor indicates a confident reserve of resistance in interconnected wall segments.