Performance Evaluation of Portal Frame System in Low-Rise Light-Frame Wood Structures

Abstract

In this paper, results are presented from a testing program focused on evaluating the performance of portal frame systems. A total of nine full-scale portal frame assemblies with six different configurations were tested under monotonic and reversed cyclic loading. The portal frames were 3.66 m in length and 2.44 m in height, with a 406-mm wall segment at each end of the portal frame. From the experimental results, it was observed that the corner joint between the header and narrow braced wall segment governs the lateral load-carrying capacity and ultimate displacement of the portal frame. Installation of metal straps considerably increased the lateral load-carrying capacity of the portal frame assemblies. Straps placed directly on the lumber framing showed increased resistance compared to those installed on the oriented strand board. Portal frames with hold-downs had a greater lateral load-carrying capacity those without hold-downs. A comparison was made between portal frames and conventional braced walls used in low-rise light-frame wood buildings. The portal frames in general have lower initial stiffness than the braced walls. A portal frame with sheathing on one side only and no hold-down has an ultimate load-carrying capacity equivalent to a 2.44-m long braced wall with hold-down. A portal frame with hold-down can on average achieve a capacity similar to that of a 4.88-m long braced wall without hold-down.