A new concept for column-to-column connections for multi-storey timber buildings—Numerical and experimental investigations

A new jointing concept for the vertical load transfer between glued laminated timber (GLT) columns in multi-storey timber buildings has been developed. The basic components of the connection are two stepped, pyramid-shaped inserts made from block-glued laminated veneer lumber (LVL), which are bonded oppositely into corresponding cavities of the jointed GLTs. The load transfer between the mating columns relies on an intermediate LVL pin, fitting into pyramid-type cavities. Beech LVL was chosen for both, insert and pin, due to its 2.2 times higher characteristic compressive strength as compared to the employed high-strength softwood GLT (GL32h). The form fit of the stepped components which are bonded together relies on high precision robotic milling and a gap-filling two-component polyurethane adhesive. Manufacturing and mechanical performance of the scalable connection was investigated with full-sized specimens, achieving up to 90% of the characteristic GLT compressive capacity of 1040 kN for a cross-section of 180 mm×180 mm. A parametric model based on the finite element method (FEM) showed a good agreement with empiric strain distributions and provided a stress-spread angle of 35° for the concentrated vertical load for an analytical design approach. The location and magnitude of tensile stresses perpendicular to the grain causing splitting failure was identified by FEM. Reinforcement by self-tapping screws proved a significant load-capacity enhancement. The mean experimental axial compressive load capacity exceeded the analytical prediction by 19%. First investigations on the rotational stiffness delivered a value of 240 kN m/rad. The column utilization due to additional directly supported floor slabs was assessed exclusively by FEM. The calculation results predict a significant reduction of the tensile stresses perpendicular to the grain to be verified experimentally.