A connection for two-way spanning cross-laminated timber-concrete composite floors

Cross-laminated timber (CLT)-concrete composite (CLTCC) floors have gained popularity in recent years due to their advantages over pure wood floors. They offer a high loadcarrying capacity, increased stiffness, improved fire resistance, vibration performance, sound insulation, and thermal mass, making them suitable for floor applications with long spans and twoway spans. However, to fully utilize the two-way spanning capacity of CLTCC floors, the minor strength axis panel-to-panel edge connections need to withstand out-of-plane bending for composite action. In this study, experimental and numerical investigations were conducted to investigate the use of steel kerf plates (K connection) and steel T-bars (T connection) as edge moment and shear connectors in CLTCC floors. The kerf plates were embedded in 139-mm-thick five-layer CLT panels to a depth of 35 mm, and T-bars were mounted with self-tapping screws to connect two CLT panels of 600 mm length from the top and LVL spline from the bottom. T-bars were connected to CLT by screws in the shear zone as shear connectors. A total of 30 test specimens were subjected to shear forces and bending moments to evaluate load-carrying capacity, rotational and bending stiffness. In the shear tests, the T connection exhibited a shear connection stiffness approximately twice that of the K connection in the minor direction, with a 46% greater load-carrying capacity. The T connection in both directions could provide the two-way composite action required in the CLTCC slab. However, the T connection serviceability stiffness in the minor direction was approximately 40% lower than that in the major direction. The bending tests demonstrated that the combination of T connection and LVL spline effectively reached the rotational and bending stiffness, as well as the loadcarrying capacity, of a continuous CLT panel with the same layup. While T and K connections achieved similar load-carrying capacity, the bending stiffness with the K connection was only half of that with the T connection. In addition, the rotational stiffness with the T connection was approximately 1.6 times greater than that of the K connection. The composite efficiency was 56% for the T connection and 7% for the K connection, demonstrating that the T connection provides composite behavior in the minor strength axis. In the numerical investigation, a sensitivity analysis was conducted to assess the factors impacting the bending capacity and deformations of CLT and CLTCC slabs interconnected by T connections including biaxial connection stiffnesses between two layers and rotational stiffness between two panels. Subsequently, a 9×12 m CLTCC slab with T connections was designed and modeled. The two-way action was predominantly influenced by the connection stiffness and rotational stiffness in the minor axis, and the proposed connection demonstrated adequate stiffness in facilitating the transfer of moment and shear forces between panels and layers.