Design Criteria for Epoxy Repair of Timber Structures

Abstract

The repair of timber structures requires the same careful engineering design as that of new structures. However, practically no information is available that allows the engineer to compute either allowable or actual stresses for repair alternatives. Based on both theoretical and experimental studies, a methodology for computing both actual and allowable glue line shear stresses is presented here. The actual glue line stress is computed as an average shear stress. The allowable stresses are given as formulas which are functions of the wood species, grain orientation, allowable wood shear stress, and lap length to member thickness ratio. Several epoxy formulations are considered and a method for evaluating other epoxies is presented. Numerical examples are given to illustrate the approach for both predicting the strength and designing a repair scheme. Through the use of the design techniques presented here for epoxy repair of timber, the engineer can rationally decide: (1) Whether the proposed repair will be structurally adequate; and (2) how to modify the design if the predicted load capacity of the joint is too low.