TESTING OF THE SEISMIC BEHAVIOUR OF A TRADITIONAL JOINT IN A WOODEN ROOF STRUCTURE

The roof timber constructions are and have been used extensively to support floors and roofs, nowadays as well as traditionally. They consist of plain timber elements and carpentry joints that work together mainly by contact pressure and friction. The structural response of roof frameworks (especially those in historical buildings) is highly dependent on the behaviour of their joints, particularly, their capacity for rotation and energy dissipation. Nevertheless, the seismic response in newly designed timber structures relies on the mechanical behaviour of connections. In historical timber structures, carpentry joints transmit forces between timber elements by direct contact and friction, whereas metal connectors, when present, only safeguard the connection against exceptional actions that could relieve contact and separate parts. Carpentry joints are built based on traditional practice based on empirical rules, or at most designed with extremely simplified models that are not supported by sufficient experimental and analytical evidence and consequently they may not comply with the safety levels that are now imposed, particularly for seismic action. With that in mind, a small research program has been carried out by the authors for characterizing the mechanical behaviour of carpentry joints. The so called birdh-mouth joint typology most frequently used in simple timber structures, with special attention to roof trusses, have been considered in the study. In the paper, some results are presented, with special attention to the rotational behaviour of these joints and to the effects of possible seismic strengthening operations in the elastic and post-elastic field.