PSI - Issue 78

Martina Sciomenta et al. / Procedia Structural Integrity 78 (2026) 253–260

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ductile shear behaviour (Schiro et al., 2018) (De Santis et al., 2022). Screws, either fully or partially threaded, can be placed perpendicularly to the floor or inclined with an angle, providing lateral, axial and deliberately combined loading capacity that enables them for a vast variety of connection configurations in any kind of solid and engineered wood product (Aicher et al., 2023).The efficiency of composite floors lies on the connectors which play a key role in assuring the effectiveness of the composite section. Specifically, the connectors should be able to transfer internal actions between the two members. If the connector is p laced perpendicular to the grain (i.e., with an inclination angle α = 90°), the resulting action on it is a pure shear force. However, when the connectors are inclined at an angle α ≠ 90°, it is subjected to a combination of shear and tensile forces. To guarantee the applicability of the section analysis, no-slip should occur between the elements' interface, and the shear connectors should be sufficiently stiff. The mechanical connectors’ characteristic features are provided by the manufacturers in the product standard (i.e. European Technical Assessment, ETA) for different types of engineered wood products and configurations. It is evident that when such connectors are used in configurations that are not specifically described by the product standards, their performance needs to be evaluated experimentally (Schiro et al., 2018) (Loss et al., 2016). In this case, the use of underutilized hardwood species, their lamination into glulam elements, and the hybrid configuration represent a novel approach that has resulted in products not covered by the screws’ ETA. In fact, up to now, most of the screws are certified and calculated only for CLT and high-density woods such as beech LVL but not for glulam. To determine strength and deformation characteristics of joints made with mechanical fasteners, push-out specimens are usually realized and tested in accordance with the reference standard EN 26891 ((CEN), 1991). In this paper, the mechanical behaviour of two types of timber-to-timber screws (VGZ and VGS fully threaded screws produced by Rothoblaas) loaded in shear was investigated for the use on hardwood glulam. The aim is to prove their effectiveness for TTC floors made of hardwood glulam elements. Furthermore, the glulam itself which was made by the selected species of hardwood and configurations, was itself a novel product, currently not available on the market. In particular, the glulam employed in this research derives from a short supply chain production aiming to establish the usability of local wood for structural purposes and to enhance the use of natural resources in central Italy. 3. Materials and methods 3.1. Specimens Push-out specimens were realized with the common double-shear layout, consisting of a central timber element flanked by two side elements symmetrically arranged and connected. The central timber elements were obtained by cutting the novel hardwood glulam beams into parts with a length of 560 mm. The side elements consisted of boards, put on stage as a single layer of planking. The experimental campaign consisted of three series of specimens; the Series #1 was made of beech in homogeneous configuration coupled with beech boards as side elements; the Series #2 was made of chestnut coupled with chestnut boards as side elements and the Series #3 was made of beech in hybrid configuration coupled with beech boards as side elements. The measured densities of the three species are listed in Table 1. All the series involve two different types of fully threaded screws: the VGZ and the VGS, both supplied by Rothoblaas. The fastener s have the same diameters (Φ=9 mm) and length (l=160 mm). The main difference is the type of head: cylindrical for VGZ and countersunk head for VGS. The spacing was maintained fixed at 200 mm and two screws per side were installed. The 45° shear-tension configuration (rather than in X-formation) to enable exploitation of the beneficial orientation of the screws.

Table 1. Density of timber species Mechanical features

Beech

Silver fir

Chestnut

704

442

547

[kg/m

3 ]

ρ m

39

22

37

St. dev

[-]

ρ κ 469 ρ m is the mean density, ρ k is the characteristic density evaluated according to EN 14358 (EN 14358, 2016) [kg/m 3 ] 621 395