This study was designed to evaluate the performance of a new wood-based portal frame system developed originally by APA with the purpose of providing alternative bracing systems to conventional prescribed details of small wood buildings. To achieve this objective, the study was divided into three components:
Study the performance of full-size portal frames with different configurations;
Evaluation of portal frame corners to optimize corner details and finally,
Develop a numerical model for portal frames to evaluate effect of the various parameters on performance and predict portal frame performance. Supplementary connections and material tests were conducted to generate input data for the finite element modelling of the portal frame.
Results from this preliminary test indicate that the lateral load carrying capacity of portal frames is approximately 75% the capacities of identical frames with hold-down. Those assemblies also had greater ultimate displacements than assemblies without hold-downs. Compared to portal frames without metal straps, the lateral load carrying capacity is slightly increased for with metal straps installed over sheathing. Same finding was observed in portal frame corner assembly tests. Full size portal frame and corner assemblies sheathed on one side without hold down had the lowest capacity among all assemblies tested. The addition of OSB sheathing to both sides of the portal frame corner has increased the moment resistance and rotational stiffness of the corner frame assembly.
Key findings from the FE modelling of portal frames with different types and locations of metal straps showed that the tensile strength of metal straps has the highest impact on the lateral load capacities and stiffness of portal frames assemblies. Portal frames assemblies with sheathings attached on both sides of the framing have approximately 30% higher lateral load capacities and stiffness than the walls with sheathings attached on one side of the framing. Moreover, it was found that it is more efficient to place metal straps directly on framing members. The efficiency is reduced if the metal straps are placed over the sheathing. The contribution of double bottom plates is insignificant. For portal frame assemblies with double bottom plates and two rows of nails fastened to the bottom plate, the stiffness and lateral load capacities are slightly increased compared to the walls with single bottom plate.