Experimental Analysis of the Influence of the Fastener Type on the Embedment Strength Parallel to the Grain in Glued Laminated Timber

Overview & Synopsis

Embedment strength is an important parameter that governs the ductile load-carrying capacity of timber joints with dowel-type fasteners. This property is dependent upon several factors, especially on the surface conditions of fasteners. In current design standards, however, the embedment strength depends only on the timber density and the diameter of fastener, though the surface conditions of dowels and fully threaded bolts are different. In this study, embedment tests for dowels, fully threaded bolts and glued-in rods in the direction parallel to the grain were carried out. Comparisons with the existing design equations in Eurocode 5 Design of Timber Structures (EC5) and American National Design Specification (NDS) were performed. It is found that the embedment strength in timber for dowels can be accurately predicted by EC5 and NDS, while the embedment strength for fully threaded bolts is underestimated. In addition, the embedment strength for glued-in rods is not addressed in the current design standards. Based on the presented experimental results, new empirical expressions for the embedment strength parallel to the grain in timber for fully threaded bolts and glued-in rods were proposed.