Cross-laminated timber (CLT) panels have been gaining popularity as diaphragm elements in mid- to high-rise construction projects. In addition, CLT-concrete composite (CCC) diaphragms have been implemented to expand the use of CLT diaphragms. To understand the behavior of CLT and CCC diaphragms, this research effort sought to characterize the cyclic, in-plane shear performance of CLT and CCC diaphragm connection systems that make use of surface spline connections between CLT panels. Tested system variables include surface spline fastener type (nails and screws) and screw spacing, concrete slab thickness, and composite screw angle.
Results from the testing program provide useful engineering values for assessment and design including elastic stiffness, peak force, and displacement ductility. These values were used to describe the damage progression, compare engineering values, and develop performance models for each tested system. Results from the bare CLT diaphragm tests indicate that common nails are a viable spline fastener alternative to self-tapping screws (STS) and that no group effect occurs for the tested STS spacings, which ranged from 100 mm to 200 mm. CCC testing, which tested the CLT to concrete load path typical of what may be seen in seismic applications in platform type of construction, revealed that diaphragms with composite screws angled at 45-degrees display higher strength and similar stiffness values compared to the ones with 90-degree screws while slab thickness does not have an impact on the strength or stiffness of the diaphragm system.