Strength and stiffness of oak pegs in traditional timber-frame joints

The objectives of this paper are to present experimental data and analytica l models to assist in the analysis and design of pegged joints in tradition al timber frames. Seventy-two simplified mortise and tenon joints were load ed to failure under compression-induced double shear. Load, deformation, an d time were recorded. All joints utilized 25.4-mm-diameter red oak pegs, ty pical of those used in modern timber-frame construction in North America. H alf of the specimens were made with eastern white pine lumber, with the rem aining specimens made of sugar maple. All specimens had 50.8 mm center piec es simulating a typical tenon. Side pieces were evenly divided into 25.4 mm and 50.8 mm thicknesses. Half of the specimens were arranged such that the center piece was loaded parallel to the grain and the side pieces perpendi cular. Grain orientation was reversed for the remaining specimens. Joint st iffness was estimated by a regression analysis of the linear portion of the load-slip curves. A model for joint stiffness was developed for use in ana lysis of traditional timber frames. The stiffness model was found to undere stimate the stiffness of typical pegged knee-brace joints by 20-30%. The yi eld theory was augmented with two peg deformation modes to develop a method for predicting failure loads. Strength predictions ranged from 16% low to 2% high in comparison with the test data.