"Timber frame moment joints with glued-in steel rods. II: Experimental investigation of long-term performance"

The pull-out performance of steel rods glued into timber is well-documented, and short-term tests by many researchers have demonstrated reliable strength. The behavior of glued-in steel rods in moment-resisting beam-column joints is much more complex because of anisotropy of wood in the connection region, discontinuity of material at the interface, and the possible effects of creep of timber and stress concentrations on the joint performance. This paper describes the results of a series of long-term load tests on moment-resisting joints between glulam members and separate load tests on the various joint components, including the epoxy itself and the timber stressed perpendicular to the grain. Different types of knee joints, with rods fully epoxied along their length or epoxied only in one member and tensioned in the other, and with different geometries (with the beam extended over the column or with the column extended past the beam) were tested. Measurements were recorded to identify time-dependent stress redistribution within the test joints, creep of the joint as a whole, and possible crushing of the timber-to-timber bearing surfaces. Local deformation of timber loaded in compression perpendicular to the grain was found to contribute to excessive joint deformations in tests in which the steel rods were not glued over their full length. The test results confirm the possibility to use the transformed section method in design as presented in the first companion paper, and address a number of issues pointed out in the same paper.