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2. Moisture-activated set-recovery of thermo-hydro-mechanically densified hardwood dowels for high-tolerance timber connectionsLei Han, Alexander Scharf, Mohammad Derikvand, Matthew Schwarzkopf, Bogdan Mitkovski, Dick Sandberg, Andreja Kutnar, 2026, izvirni znanstveni članek Opis: Conventional wooden dowel connections in timber structures rely on tight press-fit installation, which requires high insertion forces and often loosens over time due to stress relaxation. This study investigates an alternative approach that exploits the moisture-activated set-recovery of thermo-hydro-mechanically (THM) densified hardwood dowels to enable slip-fit assembly followed by self-tightening in service. To this end, European beech and black poplar were densified radially and tangentially at different compression ratios. They were then evaluated for swelling kinetics, swelling pressure, bending performance, and moisture-activated expansion using in-situ X-ray CT in water at 20 °C and 100 °C. Results show that activation kinetics can be controlled by temperature. Expansion was rapid within minutes in hot water and slower but equivalent in magnitude at room temperature. Beech outperformed poplar, with radial densification at 35 % compression ratio producing a peak swelling pressure of 5.7 MPa and a modulus of rupture of 268 MPa after activation. Poplar generated higher free expansion but significantly lower pressure due to its lower stiffness. Radial densification was consistently more effective than tangential, enhancing both expansion magnitude and pressure generation. Capillary uptake triggered expansion along the dowel length (∼30 mm in 1 h) and produced an elliptical expansion profile. Importantly, mechanical strength was retained post-activation, which confirms structural suitability. These results demonstrate that THM-densified beech dowels can offer a robust self-tightening mechanism, combining low-force installation with durable pressure generation and stable mechanical performance. This provides a viable path toward adhesive-free, metal-free, high-tolerance timber connections.
Ključne besede: THM densification, dowel laminated timber, CT scanning
Objavljeno v RUP: 28.01.2026; Ogledov: 202; Prenosov: 0
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3. 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: 243; Prenosov: 4
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4. 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: 507; Prenosov: 11
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