Static Front to Back Loading Capacity of Wood Chairs and Relationship between Chair Strength and Individual Joint Strength

The relationship between the static front to back loading capacity of chairs and the moment capacities of the joints used in their side frames was investigated. The secondary purpose of the study was to determine the effect of tenon sizes on front to back loading capacity of chairs. The moment capacities of round edge mortise and tenon L-shaped and T-shaped joints constructed of Turkish beech (Fagus orientalis L.) with cross sections and tenon sizes identical to those used in the chairs were first determined. Tenons varied from 30, 40, and 50 mm in width and 30, 40, and 50 mm in length. Joints were assembled with 65% solid polyvinylacetate (PVAc) adhesives. Front to back loading tests were then performed on the chairs according to the method adopted by the American Library Association (ALA). The results indicated that front to back loading capacity increases as either tenon width or length increases. Highest joint moment capacities were obtained when L-shaped joints were constructed with 50 mm wide by 50 mm long tenons and T-shaped joints were constructed with 40 mm wide by 50 mm long tenons. Finally, the strength of chairs could be reasonably predicted from the strength of joints.