Connections for Timber-Framed Structures - Assembly Properties and Structural Behaviour

Doctoral thesis, 1997

By tradition, the design and development of connections has focused on the optimization of strength and stiffness. The subject of this thesis is the interaction between the assembly and structural properties of connections for timber-framed structures. The concept of "Connection design for buildability" is introduced; this means that in this case connection design focuses on assembly properties while guaranteeing safety and function. The main merit of an approach of this kind is that increasing the buildability of timber structures enhances the economy and competitiveness of timber construction. The aim of the work is to evaluate this concept. This is done by investigating whether simple connections produce sufficient properties for two types of structure; a beam and a frame. Connection types which were designed to be very easy to assemble were built, loaded to failure and analysed. The concept of a beam-shoe in combination with a nail gun appear to be especially promising. A total of 57 tests on splices and beam-column connections are presented. The splices were chosen as suitable examples for use in 6 metre-span purlins. The beam-column connections were adapted to a suggestion for a 4.6 metre-span beam-column frame. The reliability of the test results was investigated in the form of numerical and analytical sensitivity studies. The concept of efficiency ratios is discussed as an objective tool for making comparisons between different connection types. Equations for the structural behaviour of a continuous beam and a beam-column frame are derived by modelling the joints as semi-rigid linear rotational springs. The test results and the design formulae are combined to evaluate the connections. According to this method of evaluation, all the simple joint types lead to acceptable behaviour in the structures. The classification of beam-column connections in terms of stiffness is discussed. A series of six tests on full-scale two-storey frames was performed. It verified that the derived design equations are reliable. It is evident from these tests that the behaviour is linear or nearly linear to very high load levels. The conclusion is that "Connection design for buildability" appears to be a feasible design approach. Properties other than structural ones and construction applications other than the two chosen here should be possible to deal with in the same manner as is done here.