The ultimate load behaviour of glued and nailed plywood web I-beams has been investigated theoretically and experimentally. In the theoretical investigation the following joint and material characteristics have been considered. The timber to plywood flange-web joints may be rigid (glued) or semi-rigid (nailed). In the rigid joint no joint slip is assumed (i.e. no strain difference between the timber and plywood) whereas joint slip is assumed in the semi-rigid joint.