A PARAMETRIC STUDY OF RACKING PERFORMANCE OF WOOD PORTAL FRAMES

Abstract:

The performance of different types of portal frame walls was studied using a finite element model that was verified with results from tests of four full-size portal frame walls. Parameters such as wall height, metal strip types and locations, bottom plates, sheathing and nailing pattern were investigated. Results indicate that for all the wall types, the lateral load capacities and stiffness are greatly reduced with the increase of wall height. Among the different metal strip types and locations, the tensile strength of metal strips has the greatest impact on the lateral load capacities and stiffness of portal frame walls. The walls with metal strips installed placed directly on framing members outperformed the walls with metal strips placed over the sheathing. For walls 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. For walls with sheathings joined at the middle of wall height and unblocked, the lateral load capacities are the same as the walls with continuous sheathings running from the bottom to the top of the walls. The stiffness is slightly lower. The two rows of nails along end studs do not affect the lateral load capacity of the portal frame walls. However, they do increase the stiffness of the walls.