Embedment Strength of Low- and Medium-Density Hardwood Species from Spain

Abstract

The embedment strength is a key parameter in the design of timber connections with metal fasteners. This property can be determined by the equations given by design codes such as the Eurocode 5, which are based on the European Yield Model proposed by Johansen, and it depends on the value of timber density among other parameters. These equations provided by design codes are based on experimental tests performed mainly in softwood species; thus, the objective of this work is to evaluate the embedment strength of two low- and medium-density hardwood species from Spain (poplar—Populus x euroamericana; beech—Fagus sylvatica) in the parallel and perpendicular to grain directions. Four different experimental test configurations were carried out according to EN 383 for each species using two different fasteners: (i) a 9 mm-diameter screw and (ii) a 12 mm-diameter bolt. Results of embedment strength were evaluated according to three different determination methods, and later compared with the current equations provided by Eurocode 5 (EC5) and new ones proposed in the draft of the new Eurocode 5 (prEC5). Results showed that current equations overestimated perpendicular to grain embedment strength for the cases studied, while the equation proposed in prEC5 for screws fitted best perpendicular to grain embedment strength. However, it underestimated the parallel to grain one because it does not consider any difference due to load-to-grain angle (α). Finally, ratios between experimental parallel and perpendicular to grain embedment strength were studied (k90), showing 30% and 44% higher values than the theoretical values resulting from k90 equations of EC5 and prEC5 for beech with screws and bolts, respectively, and 4% and 49% higher than the theoretical values for poplar with screws and bolts, respectively.