WOOD RESEARCH Volume 67, Number 4, 2022
Eliška Hřebenářová and František Wald

Comparison of mechanical properties of the eldest larch wood construction with oak wood and spruce wood

The paper discusses mechanical properties of timber for structures – most frequently used spruce wood, historically used oak wood and rarely mentioned larch wood. The main focus is on larch wood extracted from the ceiling of an immovable cultural monument from the 17th century – the determination of its age, its historical importance and mechanical properties. Mechanical properties were obtained by the standard tests in compression parallel and perpendicular to the fibres and in bending. The results of tests are compared to the mechanical properties of oak wood, of commonly used spruce wood and of recently felled larch wood.

WOOD RESEARCH Volume 62, Number 4, 2017
Anton Osvald and Milan Gaff

Effect of thermal modification on flameless combustion of spruce wood

The paper deals with the effect of heat treatment of spruce wood (Picea abies (L) Karst.) at the temperatures of 160°C, 180°C and 210°C – on the change of properties that characterize its relation to fire and burning,in particular in the phase called flameless combustion. A test method, which is sufficiently sensitive to monitor these changes, has been used for the evaluation of these changes. The results show that thermally modified spruce wood has positive assessment even in this regard.

WOOD RESEARCH Volume 62, Number 2, 2017
Pavol Halachan, Marian Babiak, Dominik Spišiak, Anatoly N. Chubinsky, Alexander A. Tambi, and Kirill V. Chauzov

Physico-acoustic characteristics of spruce and larche wood

This study deals with non-destructive measurement of wood, i.e. physico-acoustic characteristics (density, dynamic modulus of elasticity, acoustical constant, speed of sound propagation in material and logarithmic dumping decrement). We used two species spruce and larch for measurements. We took wood from two main areas: from Slovakian higher latitudes and from Russia – Siberian areas. Spruce is the main species for the boards of musical instruments and we tried to find another species to replace this one. We measured physico-acoustic properties by two devices: The ultra-sonic tester and device “MEARFA” based on searching correct frequency for each sample. The results show that spruce for top instruments has acoustic constant approx. 12 m4∙kg-1∙s-1 and the “best” value for larch was approx. 10 m4∙kg-1∙s-1. If we compare the methods of measurement of the sound velocity through samples the results for ultrasonic testing are much higher than those provided by resonance-dynamic method. The article also describes differences between physico-acoustical characteristics of sap wood and heart wood, and differences between species.

WOOD RESEARCH Volume 62, Number 2, 2017
Aurel Lunguleasa and Cosmin Spirchez

Torrefaction of lamellar panels made of oak and spruce wood species

This paper is focused on the torrefaction of lamellar panels made of wooden species of spruce and beech, with a view to noticing the influences of the torrefaction on the physical and mechanical properties. The working method highlights the special character of the lamellar panel torrefaction as compared to other torrefied products. The obtained results emphasize that the mass losses increase with the severity of the thermal-treatment condition, where as the hygroscopicity and mechanical properties of the material simultaneously decrease. The analysis of the obtained results recommends the use of these panels in humid/moist environment.

WOOD RESEARCH Volume 63, Number 6, 2018
Antal Kánnár, Laszlo Tolvaj, and Endre Magoss

Colour change of photodegraded spruce wood by water leaching

Spruce samples (Picea abies Karst.) were irradiated by strong ultraviolet (UV) light emitter mercury lamp and another series of specimens were treated with the combination of UV radiation and water leaching. The total duration of UV radiation for both series of specimens was 50 days. The colour parameters (CIE L*, a*, b*) were measured and evaluated after both UV radiation and water leaching. The increase of redness value was two times greater than the yellowness increase based on the initial value at the end of 50 days treatment. The leaching partly removed the yellow and red chromophore molecules generated by the UV radiation. The samples become slightly lighter after water leaching. The leached samples increased slightly more in yellowness and redness during the first 4-6 days of UV radiation than those of the dry series. The change of surface roughness of the specimens was monitored by diffuse reflectance infrared spectroscopy, because the change of roughness alters the light scattering properties of the surface. The roughness of the samples increased during the UV irradiation, and the tendency of roughness change mirrored that of yellowness change. The leaching reduced the roughness value in all examined cases. Good correlation was found between the hue angle and the lightness in both dry UV treatment and combined UV treatment and water leaching.

WOOD RESEARCH Volume 64, Number 6, 2019
Marija Todorović, Ivan Glišović, and Boško Stevanović

Experimental investigation of cracked end-notched glulam beams repaired with GFRP bars

In this paper, an experimental research on bending behaviour of end-notched glulam beams and their bending behaviour after repairing with glass fibre reinforced polymer (GFRP) bars is presented. Altogether five glulam beams (100 x 220 x 4000 mm) made of spruce timber classified in the strength class C22 were tested. Experiment showed that originally, the beams failed in a brittle manner due to crack opening and its propagation. Cracks in the notch details were a result of excessive tensile stresses perpendicular to grain and shear stresses. Repairing the beams with GFRP bars after their failure completely restored and notably improved their load carrying capacity (average increase of 194%). Failure mechanism after repair changed from the original brittle tensile failure to more ductile failure in bending for most beams, proving the successfulness of the intervention. This study gives an insight in rehabilitation and repair possibilities of existing structures using advanced materials like GFRP bars.

WOOD RESEARCH Volume 65, Number 4, 2020
Roman Fojtík, Viktor Dubovský, Kateřina Kozlová, and Lenka Kubíncová

Prestress losses in spruce timber

Prestressing force and its change is one of the key factors that affect wooden constructions, especially those using methods of transverse prestressing. To achieve a description of a prestress force (P) in transversally prestressed wooden constructions a simulated experiment was done. Prestressing force, external temperature, and moisture were measured during 669 days. The main goal of this article was to model the primary losses of the prestress force at the spruce element of the 138 x 138 mm cross-section with the sensor installed. For this purpose, all measurements were statistically analyzed and the period of primary loss was found. During this period the prestress force was decreasing with time mainly and the influence of temperature and moisture could be omitted. Based on this analysis a mathematical model of losses of the prestress force was found as P = 8.538-0.014.day.

WOOD RESEARCH Volume 64, Number 1, 2019
Dong Chen, WEI ZHANG, Yu-Sheng Wu, Zheng Jin, and Qian-Wei Zhang

Investigation on the mechanical properties of open-hole spruce and douglas fir

Spruce and Douglas fir are the main materials of today’s modern wooden structure buildings. In wooden structure buildings, holes often have to be created on the building components in order to reserve channels for pipelines. At present, there are no detailed studies regarding the mechanical properties of these two kinds of lumber under open-hole condition. In this paper, universal mechanical testing machine was utilized to perform three-point bending tests on small samples of spruce and Douglas fir with open-hole (opening diameters being Ø13, Ø16, Ø20 respectively) and without open-hole. The bending strength and modulus of elasticity of openhole and no open-hole samples were compared, the effects of hole sizes on samples mechanical properties were analyzed and discussed, and the samples’ failure patterns and failure mechanisms were also studied. The experiments were loaded at a constant speed 5 mm. min-1 until the sample was broken, with the loading time controlled within 2 – 3 minutes. The results showed that: open-hole had significant impact on the bending strength of both kinds of lumber. In terms of failure modes, most of the Douglas fir samples were deformed only at the compression point before failing, while the Spruce samples not only formed grooves at the compression point but also cracked at the bottom. This indicated that compared with Douglas fir, the impact of open-hole on Spruce lumber was greater, thus open-hole should be avoided on Spruce components during construction. The experimental results provided a basis for future studies on the failure modes of these two materials and also the strength design of relevant components.

WOOD RESEARCH Volume 66, Number 1, 2021
Juraj Jancík, Linda Makovická Osvaldová, and Frank Markert

Thermogravimetric analysis, differential scanning calorimetry and time-to-ignition of wood materials treated with water glass flame retardants

The paper investigates efficiency of silicate flame retardants on wooden fibres (used for production of medium-density fibreboards) and spruce boards. A simultaneous thermal analysis and cone calorimetry were used for the assessment. Specimens were treated with three different types of silicate water glass: sodium silicate, potassium silicate and modified silicate. Along with these, one sample of untreated fibres was tested in order to provide a baseline sample. As a result of the simultaneous thermal analysis, the ability of the treatments to increase the residual amount of biological char in samples during pyrolysis and ability of the flame retardant to be retained in these wood fibres was used to assess the efficiency of each flame retardant on the wood fibres.