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Ključne besede: creep, fire performance, set-recovery, stress relaxation, timber engineering, wooden dowel, wood
Objavljeno v RUP: 13.02.2026; Ogledov: 174; Prenosov: 5
Celotno besedilo (60,41 MB)
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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: 259; Prenosov: 0
Celotno besedilo (13,97 MB)
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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: 385; Prenosov: 5
Celotno besedilo (4,20 MB)
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Objavljeno v RUP: 07.11.2021; Ogledov: 2220; Prenosov: 27
Celotno besedilo (7,54 MB)

Ključne besede: heat-treatment, resin impregnation, Scots pine
Objavljeno v RUP: 24.06.2021; Ogledov: 2655; Prenosov: 54
Celotno besedilo (1,75 MB)
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