Timber Frame Moment Joints with Glued-In Steel Rods. I: Design

Abstract

Significant evidence based on experimental research exists to give designers confidence in the use of theoretical equations to evaluate the pullout strength of threaded steel rods glued into timber. However, the mechanism of load transfer through a timber frame moment joint utilizing glued-in steel rods requires more than simply understanding the tension performance of a glued-in rod. A method of evaluating joint strength for moment and axial forces based on traditional mechanics theory adapted for use with timber is presented. Formulas were derived from first principles for joint configurations, with extended columns or with extended beams and with various types of construction (i.e., with rods fully glued along their entire length or only glued in one of the two members connected and then tensioned). The design method also considers the effects of time-dependent deformation in timber at bearing interfaces and the effects of stress concentrations imposed by the steel rods on the timber. Some open questions that deserve further investigations are highlighted, as well as some possible details to optimize joint performance while retaining ease of assembly. The approach provides a methodology for joint design that has been successfully used in many projects.