Experimental study comparing the behaviour of steel truss plates and birch plywood inserts in ridge joints on glued laminated rafters

The present paper reports on an analysis of the mechanical performance of two flat joining systems used in roof members made of glued laminated timber. Six pairs of laminated timber rafters for a double-pitched roof with a 100xl80-mm cross-section, a 6.00-m span and a height of 1.00 m were subjected to full-scale four-point bending. In three of the specimens the rafters were joined at the ridge with a birch plywood insert, while in the other three the connection was secured with a fitting consisting in a standard flat steel truss plate. The objective pursued was to evaluate the possibility of replacing the steel fittings with birch plywood inserts. The approach adopted to reach this objective was to compare the strength of the two joint pieces and the deformation generated in the overall structure during strength tests. The results proved to be highly satisfactory in terms of both the bearing capacity and the stiffness of the structures tested.