Round shaped connectors: a new connection system for CLT and hybrid structures

The use of mass timber and in particular Cross Laminated Timber (CLT) has rapidly increased within the last twenty years, encouraging companies and researchers to develop connections systems for this construction technique. Various connectors, specifically intended for CLT structures joints, are already available and cover the whole size range of construction. The optimization of such connectors, primarily focused on enhancing stiffness and resistance (e.g. using thicker steel plate with higher strength grade or inclined fully-threaded screws instead of nails), often produced an unintended consequence: the reduction of ductility. On the other hand, connections specifically designed to ensure an adequate energy dissipation required complex production processes and/or installation on-site. The new round shaped connectors presented in this paper combine stiffness and resistance provided by radially arranged fully-threaded screws and ductility obtained from the deformation of a circular tubular steel profile. The novel connection system guarantees easy installation and the chance to disassemble the structure at the end of life, respecting Design for Disassembly (DfD) principles. Most joints (e.g. wall-to-wall, floor-to-floor, wall-to-floor, wall-to-foundation) in CLT structures can be made by using these novel connectors. The results of a series of monotonic experimental tests are presented in this paper. An analytical calculation method has been developed and a resistance domain proposed to properly design the connection for multi-directional loads.