Load-bearing wood connections using birch plywood : An experimental study of birch plywood gusset plates behaviour with mechanical connectors

Abstract: A growing sustainability concern is pushing the construction industry to seekalternative materials with lower environmental impact. In the last decade useof wood as load-bearing construction has become a common trend, however,connections of timber elements are still performed by the use of steel plates.An alternative to this could be using hardwood plywood instead of steelgusset plates. Connections with plywood are expected to reach a similarcapacity and reduce the environmental impact of wooden construction evenfurther. Hence research on plywood as a load-bearing construction materialis required in order to be able to design and use such connections in reality.Since birch plywood has high strength, it was chosen to study its’ loadbearingcapacity in dowelled connections with wood elements. The aim wasto analyse birch plywood failure modes and load capacity dependence on thevariation of plywood face grain angle and mechanical fasteners positioning inthe connection. The study was conducted with a total of 36 specimens of 4 different nailpatterns and 3 plywood load-to-face grain angle directions: 0°, 22.5° and 45°.These specimens were pre-designed to have failure modes either in block shearor net tension in the plywood board. They were later tested in the laboratory byapplying a tension load. Testing results showed that despite the prediction ofblock shear in some of the specimens, plywood plates always had net tensionfailure mode. Also, especially for 0° of face grain angle, plywood specimenswith wider dowels placement in connection resulted in significantly higherload capacity than narrow ones. This showed that the spreading angle of theload plays an important role in the strength of the connection. Additionally,it was observed, that 45° grain-to-load angle specimens, which had the lowestpredicted load capacity, resulted in similar values as 22.5° specimens. Thisimplies that there is no significant effect on connection strength due to plywoodgrain angle variation when it is not parallel to the applied load.