SEISMIC DESIGN AND EXPERIMENTAL INVESTIGATION OF A NEW TIMBER HOLD-DOWN CONNECTION

Timber connections made with hold-down are usually adopted for timber wall to foundation connection at the edges of the wall to restraint the possible overturning moment (due to rocking) which can occur by applying a horizontal force to the panel (e.g. under seismic action). The main components of the connection are the steel plate fastened to the panel via threaded screws or nails and the anchor system to the concrete foundation. As such, the connection behavior under seismic loading is characterized by the contemporarily contribution of different resistant mechanisms, i.e. (i) laterally loaded timber screws or nails; (ii) axially loaded steel plate; (iii) axially loaded anchor in concrete. The former has been basically neglected in past investigations having anchored the hold-down with steel bolt directly to the strong floor. However, the design of the anchor should be considered as crucial when it comes to capacity design, especially in case of narrow foundations (edge failure) and post-installed anchors when the resistance is highly reduced with respect to steel bolt capacity. Moreover, the overall dissipative performance might be affected by the anchor’s displacement. An innovative hold-down connection has been designed to promote steel failure of the axially loaded plate. The plate’s geometry has been optimized such that capacity design rules according to Eurocode 8 can be applied. Additionally, a target displacement requirement is addressed, and the stretch length is defined accordingly. The whole connection is tested against cyclic loading and results show enhanced performances with respect to standard configuration. In particular, brittle mechanism such as concrete-cone failure of the anchors and splitting of timber are prevented. The paper discusses the experimental results for different type and size of the anchor, also the size of the optimized steel plate is considered as a parameter.