Stiffness of dowel-type timber connections under pre-yield oscillating loads

Abstract

The dynamic behaviour of timber structures in service is becoming a more important consideration in design as modern engineered wood products allow longer spans and taller timber buildings, which can be sensitive to dynamic loading such as that from wind or footfall. Connections in timber structures have a pronounced effect on their structural behaviour. In dowel-type connections, the fasteners bend under load and embed into the surrounding timber and, since embedment is a nonlinear process, the stiffness of those connections varies depending on the nature of the applied load. Here, singledowel connections are tested under cyclic loads representative of in-service vibration. One-sided and reversed cyclic loads are applied. The specimen stiffness is observed to reduce with the amplitude of one-sided cyclic load.For small-amplitude one-sided load, the specimen stiffness is seen to tend towards that predicted by an elastic model, and an analytical elastic model is presented to represent the embedment resistance of the timber and the behaviour of the connector.

Nonlinear pre-yield modal properties of timber structures with large-diameter steel dowel connections

“…A series of tests was carried out investigating the response of a single dowel-type connector to cyclic loads, the results of which are presented by Reynolds et al [15]. Some of the results from that paper are presented here with a different focus, to investigate how nonlinearity in the behaviour of connections may affect the dynamic response of the cantilever beams and frames tested in this study.…”

“…The amplitude of the two cycles can be expressed as an R-ratio, which is the ratio of the highest to the lowest load in the cycle. Reynolds et al [15] tested three specimens at R-ratios of 1.2 and 10 for specimens loaded in tension and compression, parallel and perpendicular to the grain. Here we compare the tests with a mean value of approximately 20% of the predicted yield load of the connection, to be of relevance to the frame and cantilever tests.…”

“…The holes in the timber were drilled using a 12mm-diameter auger drill bit, and the dowels were observed to fit tightly into the hole. As discussed further in [15], it is considered that nonlinearity in dowel embedment under cyclic load is primarily due to the nature of the contact surface between steel and timber, with any lack-of-fit between dowel and timber resulting mainly in additional initial displacement. In the cantilever beams and the supports of the frames, the steel plate was welded to a bracket fixed to the laboratory strong wall.…”

“…Tests on individual dowel-type connections by Reynolds et al [15] showed that, for cyclic loads with peak loads of 20% or 40% of the yield load, stiffness nonlinearity was evident, and stiffness was observed to reduce with an increase in amplitude of cyclic load.…”

Briefing: Super tall timber – Oakwood Tower

“…The importance of directing loads to the lateral load resisting system is compounded in a timber structural system due to the reduction in stiffness in typical timber connections when subjected to load reversal (Reynolds et al, 2014). This provides a strong incentive to minimise interior vertical load paths by maximising clear spans and directing vertical load into a lateral load resisting system at the perimeter.…”