Half hole and full hole dowel embedment Strength: A review of international developments and recommendations for Australian softwoods

Abstract

Embedment strength is an essential system property of the European Yield Model which is commonly used to predict the ductile capacity of timber joints using dowel-type fasteners. This paper presents a comprehensive review of international embedment test methods and prediction formulae in design codes and literature, as well as an experimental study to evaluate the impact of different test methods parallel to the grain. A total of 224 full hole (FH) tension and half hole (HH) compression tests were conducted according to AS/NZS ISO 10984.2 on Australian sawn softwoods (Radiata Pine and Southern Pine) to compare embedment strength resulting from FH specimens sized to EN 383 and HH specimens sized to ASTM D5764, respectively. The results were compared to dowel embedment strength formulae from literature, those contained in Eurocode 5, the National Design Specification (NDS) for Wood Construction, and the respective joint group strength values contained in AS 1720.1, which are based on empirical test data. It was found that all strength prediction models were non-conservative except for a formula proposed by Smith et al. in 2004, which was based on FH tension tests in Australian Radiata Pine and Slash Pine. Furthermore, a strong correlation between timber density and embedment strength was found for both test methods, however, only FH tests displayed a correlation between dowel diameter and embedment strength, which is consistent with the embedment strengths formulae currently contained in Eurocode 5 and the NDS.