Experimental investigation and theoretical analysis of hybrid notch-screw shear connectors used in timber-UHPC composite structures

The composite structure comprising glued laminated timber (GLT) and Ultra-high-performance concrete (UHPC), known as (GUCC), offers a sustainable construction solution by reducing deadweight, enhancing durability, and increasing span capacity compared to the traditional glulam-concrete composite structures. This paper presents an experimental investigation into the shear behaviour of hybrid notch-screw (HNS) shear connectors used in GUCC. Eight sets of push-out specimens, varying in screw numbers, notch length, notch depth, and timber length in front of the notch, were prepared and subjected to direct shear testing under monotonic loading conditions. The experimental investigation findings revealed that the primary failure modes in HNS connectors were UHPC shear failure and a combination of glulam shear and compression failure. The length and depth of the notch were found to significantly influence the shear capacity and slip modulus of the specimens incorporating a combination of a notch and two screws. Increasing the number of screws in the connection produces effects similar to extending the connection length. Specifically, when two screws are embedded in a single UHPC notch, the ultimate bearing capacity and initial stiffness are enhanced by 23.3 % and 50.83 %, respectively, compared to the configuration with a single embedded screw. Furthermore, theoretical analytical formulas were proposed to predict the shear capacity and the slip modulus of the HNS connectors in GUCC structures. The research outcomes furnish valuable design guidance for GUCC structures using HNS connectors, contributing to the advancement of sustainable construction practices. • The shear behaviour of hybrid notch-screw (HNS) shear connectors used in glulam-UHPC composite (GUCC) structures was investigated. • The influence of screw numbers, notch length, notch depth, and timber length in front of the notch on the HNS shear connectors was studied. • Theoretical analytical formulas were proposed to predict the shear capacity and the slip modulus of the HNS connectors in GUCC structures • Design proposals concerning shear capacity and slip modulus for HNS connectors were presented.