Behavior and Modeling of Wood-Pegged Timber Frames

Traditional timber connections with wood pegs are encountered in the renovation and rehabilitation of historic wood structures and in the construction of new structures where rustic appearance and traditional methods are desired. This study examined four types of traditional connections: mortise and tenon, mortise and tenon with a shoulder, mortise and tenon with a shoulder and a knee brace, and fork and tongue. A total of 60 specimens, primarily white oak and Douglas fir, were tested. About a quarter of the specimens were assembled and allowed to season under simulated in-service load. All specimens were tested under simulated gravity load up to failure or to about five times typical design load. Some knee-braced specimens were retested to simulate lateral loads. Test results showed that joint behavior is primarily linear. A tightly fitting joint carries load with less peg damage than a loose joint allows. A mortise and tenon with a shoulder performs better than a mortise and tenon or a fork and tongue. At typical occupancy sustained live plus dead load levels, the effects of warping and checking caused by drying shrinkage overshadow any damage caused by the sustained load. Analysis of structures employing these connections requires that the behavior of the wood-pegged joints be included in a reasonable manner. In frames without knee braces, the joints can be modeled as pinned connections. In frames with knee braces, the post-to-beam and knee-brace connections can be modeled as pinned, although the reduction in effective axial stiffness of the knee brace caused by the wood pegs must be included. The effects of shear deformations should be incorporated into the analysis.