1. Experimental and analytical evaluation of shear capacity of reclaimed timber connections with thermo-mechanically densified wooden dowelsMohammad Derikvand, Donya Bazyar Khoshroodi, 2025, izvirni znanstveni članek Opis: The reuse of reclaimed timber in structural applications is increasingly recognized as a strategy to extend ma- terial life cycles and reduce waste. Particular attention has recently turned to reusing reclaimed timber in adhesive-free laminated products with wooden dowels, where connection performance is critical. The aim of this study was to investigate the mechanical performance of double-shear connections assembled from reclaimed spruce timber using thermo-mechanically densified wooden dowels. The dowels were first evaluated in bending and embedment tests on lamellae made from both reclaimed and virgin spruce timber. The shear capacity of the connections was then evaluated in three layups: two homogeneous (all-reclaimed lamellae and all-virgin spruce lamellae) and one hybrid (reclaimed side lamellae with a central virgin spruce lamella). Analytical predictions were performed based on the draft of the new Eurocode 5, however, with two alternative definitions of dowel bending resistance (ultimate moment Mu and yield moment My), and three alternative definitions of embedment strength (f 0.05d h calculated using the 0.05 d offset method, f Fmax h calculated from Fmax, and f 0.8Fmax h calculated from 0.8 Fmax). The three lamellae layups exhibited relatively similar mean capacities (7.3–8.3 kN). The all-reclaimed connections were on average 13 % stronger than the other assemblies, but this was not statistically significant. Among the model input variants, Mu with f 0.05d h showed the closest agreement with the experimental mean values, while My with f 0.05d h led to more conservative predictions preferable for design. In both cases, excluding outliers from the embedment test results reduced overestimation in the predictions. All other input variants overestimated the shear capacity. Overall, both homogeneous and hybrid connections with reclaimed timber lamellae performed comparably to virgin timber connections and exhibited predictable mechanical behavior.
Ključne besede: reclaimed timber, wood densification, structural reuse, embedment strength, dowel connections, European yield model, Eurocode 5
Objavljeno v RUP: 17.12.2025; Ogledov: 162; Prenosov: 2
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2. Size effect on bending strength and failure modes of finger-jointed timberMohammad Derikvand, Michael David Burnard, Donya Bazyar Khoshroodi, Rok Barbič, Marko Vouk, Andreja Kutnar, 2025, izvirni znanstveni članek Opis: Finger-jointed timber boards for cross-laminated timber production are typically assigned the same characteristic bending strength (fm,j,k) if produced from the same strength class, regardless of differences in their cross-sectional dimensions. To validate the relevance of this approach, this study investigated the effects of cross-sectional dimensions on the bending performance of finger-jointed timber produced from spruce (strength class: C24). A large industrial dataset of 1100 specimens, with seven thicknesses (ranging 20 to 40 mm) and variable widths, were statistically analyzed. The bending tests were performed with a constant span-to-depth ratio (l/h = 18), meaning thinner specimens had a shorter test span. Bending strength was modeled with Bayesian multilevel linear model, and the proportions of three quality-control failure modes (joint interface failure, joint base failure, and outside-joint failure) were analyzed with a zero-one-inflated Dirichlet regression. Based on the results, all groups with n ≥ 100 exceeded the declared fm,j,k of 27.6 MPa, with characteristic strengths of 43.7 MPa (+58.3 %), 40.0 MPa (+45.0 %), and 38.3 MPa (+38.8 %) for the 20-, 30-, and 40-mm thickness groups, respectively. Thinner specimens demonstrated higher bending strength with convincing evidence (pairwise contrasts PD = 100 % with 95 % HDPIs entirely below zero), while width had no credible effect (PD < 95 %). Dirichlet regression revealed shifts in failure mode proportions with varying strength. Higher bending strengths were associated with a higher proportion of joint interface failure. Outside‑joint failure was observed with a higher proportion in lower-strength and thicker specimens. Overall, assigning uniform fm,j,k to various cross-sectional dimensions proved to give adequate safety margins. Beyond the uniform fm,j,k, however, statistical evidence of a size effect on both bending strength and failure modes was observed. The magnitude of the observed size effect reflects the combined influence of increasing thickness and test span under the current quality control bending test regime, which means a coupled change in stressed volume and geometry rather than a pure cross-section scaling effect. These findings are relevant to flatwise four-point bending tests on finger-jointed boards from industrial production made with visually graded C24 spruce with thickness ranging 20 to 40 mm.
Ključne besede: wood, finger joint, strength
Objavljeno v RUP: 18.11.2025; Ogledov: 309; Prenosov: 5
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3. Push-out resistance of threaded wooden dowels in cross-laminated timber with hardwood cross-layerLei Han, Mohammad Derikvand, Jakub Michal Sandak, Martin Hladnik, Dick Sandberg, Andreja Kutnar, 2025, izvirni znanstveni članek Opis: Europe is experiencing a shift in timber resource availability, with a decline in softwoods and an increase in hardwoods, creating a need to explore the utilisation of hardwoods, particularly in construction, where softwoods have traditionally been predominant. This research aimed to assess the potential of using hardwood in hybrid, doweled cross-laminated timber (DCLT) fabricated with pre-dried threaded beech dowels. The objective was to evaluate the push-out resistance of beech dowels in a three-layer DCLT with spruce in the outer longitudinal layers and beech, poplar, or spruce in the cross-layer. The DCLT specimens were conditioned at various temperatures and relative-humidity (RH) levels before the push-out test. The specimens with beech cross-layer exhibited a higher push-out resistance than those made entirely of spruce. In contrast, using poplar in the cross-layer showed no considerable difference in push-out resistance compared to using spruce. Exposure to 70 °C and 10% RH for three days decreased the push-out resistance in all groups due to extreme shrinkage of the lamellae, whereas exposure to 20 °C and 65% RH for either 60 days or 240 days resulted in higher push-out resistance for DCLT with a beech cross-layer.
Ključne besede: DCLT, underutilised species, hardwood, dowel
Objavljeno v RUP: 12.09.2025; Ogledov: 460; Prenosov: 11
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