Monotonic and cyclic pull-pull tests on dowel-nut connector in laminated veneer lumber made of European beech wood

Abstract

The findings from tests on steel dowel-nut connector in Laminated Veneer Lumber (LVL) bar are reported. Test specimens were prepared using LVL members made of European beech wood (Fagus sylvatica L.), showing a square cross-section of side length 50 mm and veneers arrangement comprised of 18 layers with the grain oriented in the bar longitudinal direction. The tested connection consisted in a 12 mm-diameter longitudinal threaded rod of class 12.9 steel (nominal yield strength fyb = 1080 MPa) screwed into a transverse 20 mm-diameter (=d), 50 mm-long dowel-nut. Three monotonic compression tests and 42 pull-pull tests were carried out. Among these latter, 22 were monotonic and the remaining 20 were cyclic. The dowel-nuts were also made of class 12.9 steel, with the exception of those used in ten cyclic tests, which were of grade S355 steel (fyk = 355 MPa).Preloading the connection with a controlled tightening increased both tension and compression stiffness. Greater tensile strength and smaller results scatter were found for dowel-nut axis orthogonal to the veneers. Load-carrying capacities obtained for dowel-nut end distances of 2.5d and 5d were 33% and 100%, respectively, those obtained for 7.5d. In cyclic tests, no significant increase in the strength degradation was observed due to cyclic loading. In the case of grade S355 dowel-nut, evident plastic deformations were achieved in the connector for end distances 5d and 7.5d. However, this did not influence neither strength nor corresponding displacement.