A new connection system for minimizing seismic damage in cross laminated timber (CLT) structures

The paper presents the outcomes of an experimental testing campaign on a new connector for wall-wall, wall-floor-wall and wall-foundation connections in medium-rise Cross Laminated Timber (CLT) buildings. The connector is intended to resist both the tensile and the shear forces that are typically borne by hold-downs and angle-brackets through screws oriented in different directions. On one hand, the connector is designed to respond elastically to the inertia forces originating from seismic events that are compatible with current code requirements, hence limiting the damage to both structural and non-structural components. On the other hand, in case of earthquakes of unexpected intensity, the connector is designed to exhibit a pseudo-ductile failure mode and thus avert sudden, brittle failures. Monotonic and cyclic tests were performed to evaluate the response of the connector under various loading conditions. A finite element model was developed and then validated on the experimental evidence, with the aim of creating a tool for future optimization of the connector. Additional tests on single screws were performed to assist the design of the laboratory testing and to calibrate relevant parameters of the numerical model. Furthermore, a simplified analytical formulation was developed for a preliminary estimation of the capacity of the connector. The laboratory testing produced promising results in terms of connection capacity and overall behaviour, and confirmed the predictions obtained from the numerical models.