Joining wooden rafters with plywood gusset plates using helically threaded nails to form roof trusses has been widely developed in recent years. Actually, the nailed member has proven to be extremely strong and stiff, but it is not perfectly rigid. The effect of non-rigidity of joints in resisting bending and thrust are investigated in this paper. The purpose of this study is to determine the rotation and slip of truss members relative to plywood gussets which influence the moment, shear, and axial load of each member. Experimental work was conducted on several timber joints in an effort to determine their actual characteristics. The theoretical analysis of relative rotation was based on the assumption that a rafter member is supported by a continuous elastic foundation; i.e. by equally spaced nails. It yields results which are reasonably close to those found experimentally. The Moire Fringe effect was introduced to measure the rotation of the wooden chords relative to the gusset plates of small model joints. A model truss with semi-rigid joints was tested. Strain were measured with SR-4 gages and deflections with dial gages The results were applied full scale designs by model analysis techniques / M.S.