Hysteretic Response of Metal Connections on Hybrid Cross-Laminated Timber Panels

The development of cross-laminated timber (CLT) has created new opportunities for the use of lumber from low-grade and low-density species in structural applications. In order to ensure the structural viability of CLT panels with such material, hybrid layups have been proposed, in which the low-grade and low-density lumber was placed in core layers, while high-grade (#2 or better) and high-density lumber was used in the face layers. One major criterion in the evaluation of hybrid CLT for structural uses is their performance with metal connectors, which plays a major role in seismic behavior of CLT structures. Previous studies have shown that when properly designed and detailed, CLT buildings can perform well during seismic loading, and they emphasized the role of connections in structural design, modeling, and analysis of CLT buildings. In the United States, the existing design standards, however, do not account for the variation of density in wood when estimating connection performance characteristics. This paper presents the results of a testing program developed to estimate the hysteretic response of selected CLT connection systems applied on hybrid CLT panel layups. The cyclic performance of three connection systems readily available in the North American market was determined using a modified Consortium of Universities for Research in Earthquake Engineering (CUREE) cyclic loading protocol. Results from the testing program indicate that a statistically significant difference exists between results of the connections systems on hybrid and conventional panel layups only when the failure mode involved fastener damage that penetrated the core of the hybrid CLT panels. Analytical results are also provided for cyclic force-deformation response of the connections for which modeling parameters have been calibrated using a proposed semiautomated calibration algorithm.