Experimental evaluation of mass timber composite panel connections: screw-glued, glue pressed, and SHARP metal

The current paper investigates the performance of three glue-pressed, five screw-glued, and one SHARP metal plate shear connection configurations under monotonic loading to characterize the overall behaviour and structural properties, and evaluate the suitability of these connections for use in mass timber composite (MTC) panels. Two adhesives, polyurethane (PUR), and phenol-resorcinol-formaldehyde (PRF), were used for glue-pressing and two adhesives, PL Premium Max (PL) and PUR, were used for screw-gluing. On average, the maximum shear stress for glued connections (PL, PUR, and PRF) ranged from 4.17 MPa – 5.90 MPa, while the SHARP plate configurations had an average maximum shear stress of 1.32 MPa. Screw-glued specimens with PL Premium Max exhibited the most consistent behaviour across all the configurations, indicating good repeatability and gap-filling capabilities. The average maximum shear stress for the glue-pressed specimens (PUR and PRF) was consistently above 5.0 MPa and had higher average stiffnesses than the screw-glued PL Premium Max configuration, albeit with greater stiffness variability. All screw-glued connection configurations achieved comparable average maximum shear stress (4.37 MPa – 5.20 MPa). Both screw-glued PUR configurations (150 mm and 300 mm screw spacing) had higher stiffnesses than the PL Premium Max connections; however, larger stiffness variability was also observed. Laminated veneer lumber also showed to be a promising material for the web, with an average maximum shear stress of 5.20 MPa and comparable stiffnesses to the other glue-pressed PUR and PRF configurations with glulam webs. An initial low-stiffness region (initial slip) was observed in over half of the glued specimens and was attributed to small initial movements of the specimen within the test setup. When applied to a representative 10 m long CLT-glulam ribbed panel, all connection configurations achieved near full composite action between the elements (>96 %). Overall, all the connections studied herein showed promising potential for long-span MTC panels in terms of stiffness, strength, and constructability. • Screw-glued connections performed comparably to glue-pressed connections. • Screw-glued PL Premium MAX adhesive showed promising performance and repeatability. • Screws spaced at 300 mm provided adequate clamping pressure spread with 105 mm CLT. • All connections achieved high degrees of composite action in MTC panel design. • Average SHARP plate failure was 1.32 MPa with similar stiffness to inclined screws.