Wood Layers Research Articles

Impact noise calculations of CLT constructions using finite element

Cross-laminated timber (CLT) consists of multiple glued layers of wood, which have perpendicular orientation with respect to adjacent layers, and it has become an important building material due to its light weight, strength, and sustainability. One problem with CLT constructions is the impact noise, which for a bare CLT floor is poor. There thus is a need for calculation tools that can predict impact noise level of such floor constructions. For composed constructions, finite element is a flexible and usable tool. However, to simulate real measurement scenarios, the force produced by the ISO tapping machine then needs to be estimated. This paper revisits this estimation and performs calculations of the impact noise level of a CLT floor, and compares this with measured results.

Palynological, tephra, and 14C records from southern Kaitoke, Great Barrier (Aotea) Island, New Zealand, since c. 30,000 cal. yr BP

ABSTRACT Here we present results of the last remaining three, unreported pollen and stratigraphic profiles from our previous investigations on Great Barrier Island from southern Kaitoke. The 14C and pollen data extend the island’s previous maximum pollen-vegetation date from c. 7000 cal. yr BP to close to the end of MIS 3 c. 30,000 cal. yr BP. The oldest 14C date (34,380-28,190 cal. yr BP) and the presence of secondary deposition fragments of Rotoehu Tephra in the basal brown sands and nearby dune deposits implies their formation between c. 30,000 and 45,000 yr BP. The basal sand deposits and palynology in Profile 1 indicate that the site was close to sea-level at the time. Subsequently, the sediments reflect the Last Glacial Coldest Period, characterised by increased Fuscospora pollen. Following the relative stability of the mid-Holocene high sea-level stand, alternations between drier and wetter (freshwater) conditions, with depositional hiatuses, are congruent with evidence for erratic sea-level falls causing blockage of coastal drainage and rear-dune flooding since c. 2,700 cal. yr BP; layers of preserved wood and in-situ stumps overlying firmer palaeosols were followed by fresh-water peats at two of the sites reported here and other, previously reported sites. Polynesian settlement and forest clearance occurs around the time of the 1314 ± 12 AD Kaharoa Tephra, consistent with the project’s previous reports, and with the timing from elsewhere in New Zealand.

Finite Element Modeling of the Dynamic Response of Plywood.

Modeling the dynamic properties of wood and wood-based composites is a challenging task due to naturally growing structure and moisture-dependent material properties. This paper presents the finite element modeling of plywood panels' dynamic properties. Two panels differing in thickness were analyzed: (i) 18 mm and (ii) 27 mm. The developed models consisted of individual layers of wood, which were discretized using three-dimensional finite elements formulated using an orthotropic material model. The models were subjected to an updating procedure based on experimentally determined frequency response functions. As a result of a model updating relative errors for natural frequencies obtained numerically and experimentally were not exceeding 2.0%, on average 0.7% for 18 mm thick panel and not exceeding 2.6%, on average 1.5% for 27 mm thick panel. To prove the utility of the method and at the same time to validate it, a model of a cabinet was built, which was then subjected to experimental verification. In this case, average relative differences for natural frequencies of 6.6% were obtained.

Enhanced syngas production from wood biomass by the catalytic packed bed of dolomite, limestone and olivine

Wood biomass was a promising renewable energy source that achieved carbon neutrality and alleviated the energy crisis. To enhance the conversion efficiency of wood to hydrogen, the catalytic combustion system of natural ores (dolomite, limestone and olivine) and wood chips was established. And the effects of the type, location, calcination temperature, content and diameter of catalysts were investigated on the temperature distribution and gas production. The results indicated that the combustion temperature of the hybrid bed was significantly increased with the catalyst addition. The dolomite and limestone particles promoted the hydrogen production, and the mole fractions of hydrogen were improved by 75% and 42%, respectively. When the dolomite was located above the wood layer, the hydrogen fraction was greatly higher than that of mixing with the wood. As the dolomite content increased, both of the hydrogen mole fraction and release time were enlarged obviously. Furthermore, the wood chips and dolomite particles with smaller diameters contributed to syngas production. And the hydrogen decreased with the increasing of air velocity when dolomite addition, which achieved the maximum of 11.2% at the velocity of 2 cm/s.

Experimental investigation of traditional Kath-Kuni wall system and traditional joints

In the Indian Himalayan region, the traditional vernacular construction system is a centuries-old system that is considered a seismic-resistant construction system. This practice is developed in the area over a period of time by the local communities and is never conventionally engineered. Hence, it is important to know about the behaviour of traditional construction systems and key features associated, under gravitational and lateral loading conditions. In the present research, experimental studies have been done on the full scale as well as scaled-down kath-kuni wall specimens, under push-over loading conditions, to characterize its overall behaviour, deformation and earthquake-resisting features. The failure of the kath-kuni wall was governed by friction capacity reduction followed by internal rotation in wooden layers. The kath-kuni system showed high ductile behaviour and the behaviour factor R was calculated as more than 5.4, and was compared with conventional brick masonry. The joints in the kath-kuni wall system have been identified and separate experimental studies, with varying member sizes, have been conducted to find out behaviour and capacity of these traditional joints upon loading. Analytical equations, to calculate capacity, have been proposed and compared with experimental results. The coefficient of friction was found to be varying in between 0.42–0.8 for different surfaces under constant overburden.

A hybrid solar/biomass active indirect kiln dryer for timber in the Democratic Republic of Congo

This paper presents a small-scale pilot project in the Democratic Republic of Congo of a hybrid kiln dryer for sawn timber powered by solar and biomass energy. The chamber’s thermal insulation comprised layers of vetiver grass, wood and clay, 100% biodegradable. Sun collectors and a supplementary furnace-burning biomass from the nearby sawmill provided the heating energy, while photovoltaic panels supplied electric energy for ventilation and electric devices. The climate was controlled through actuators operated by an electronic system for industrial kiln dryers. Despite relatively high production costs, primarily due to the photovoltaic system, the kiln allowed for good use of local labour and materials. Preliminary tests indicated an improved drying potential of the kiln compared external conditions with a consequent lower drying time and final MC. Data emphasised the influence of thermal energy in the drying rate: the extra power given by the furnace increased the drying rate from 0.4 to 1.4% day−1. The cost of energy ($/kWh) was calculated as 0.009 for the furnace, 0.05 for the solar collector and 0.14 for the photovoltaic. The conversion efficiency of solar collector resulted to be 48% against 14% of photovoltaic.

Wood sandwich softening behavior via coupling of moisture and heat

The controllability of the position and thickness of the compressed layer in the sandwich compression wood is primarily based on the yield stress distribution during a hydrothermal treatment. In this study, the variation law of the yield stress of poplar wood was analyzed in the moisture content (MC) range of absolute dryness to saturation and the temperature range of 30–210℃. A prediction model of wood yield stress response to MC and temperature was developed and the formation of sandwich compression was analyzed. The yield stress of the wood was influenced by the thermal effect and plasticizing effect. In the process of increasing temperature and MC, the yield stress decreased gradually. And the yield stress change rate was 0.29–0.46 MPa in the MC range of 5–10%. The prediction model of wood yield stress was developed by a multiple linear regression analysis. This example demonstrated that coupling distributions of MC and temperature were formed upon heating at 180℃, which led to a gradient distribution of the glass transition temperature and yield stress inside the wood. This phenomenon resulted in the sandwich softening behavior under the coupling of moisture and heat, which was the key formation mechanism of sandwich compressed wood.

EXPERIMENTAL AND ANALYTICAL INVESTIGATION OF THE EFFECT OF LAYER NUMBER AND THICKNESS ON THE BENDING PROPERTIES OF GLULAM BEAMS

Wooden material is used in structural elements due to its many positive properties. Recent years have witnessed a surge in research directed toward enhancing the mechanical properties of wooden beams through the utilization of materials like steel plates and fiber reinforced polymers (FRP). Layered laminated timber, a composite material crafted from wood, serves as a testament to this endeavor. These laminated timbers constitute intricate engineering elements, fashioned from layers of wood characterized by distinct levels of strength and hardness, systematically arranged as per established guidelines. The present study is geared toward a comprehensive examination of the bending characteristics exhibited by glued beams, fashioned from spruce trees, encompassing six distinct sizes and varying layer counts. The manufacturing process yields beams with diverse cross-sectional profiles, including 3-layer and 7-layer variants. By performing 4-point bending tests of the beams, maximum load carrying capacity, bending strength, and elasticity modulus values were obtained experimentally. In addition to the experimental analyses, numerical models of the produced beams were created using the finite element analysis program, and static analyses were performed. In the experimental results, it was observed that the bending properties of the beams increased as the number and size of layers increased. It was determined that the maximum load carrying capacity, bending strength, and elasticity modulus values obtained as a result of experimental and numerical analysis were very close to each other. Numerical analysis results showed that beams produced with various number of layers and thicknesses can be simulated. It has been determined that the results obtained by creating numerical models instead of experimental analyses for this type of wooden beam may be sufficient.

Izrada laminata upotrebom kompozita od drva i otpadne gume

This study aimed to develop laminate flooring composite using a combination of wood and waste tire rubber (WTR). Plywood panels were produced by using beech (Fagus orientalis), alder (Alnus glutinosa), and poplar (Populus) veneers in a 7-ply configuration. To enhance the physical-mechanical properties of the panels, three loadings of nano-SiO2 (0, 2, and 4 wt%) along with 2 wt% of hexamethyldisilazane (HMDS) were added. Commercial urea-formaldehyde (UF) resin and methylene diphenyl diisocyanate (MDI) were used to bind the wood layers and rubber layers together. The mechanical properties, including modulus of rupture (MOR), modulus of elasticity (MOE), impact strength (IS), hardness strength (HS), and physical properties, such as density (D), water uptake (WU), and thickness swelling (TS), were evaluated. The results showed that increasing the WTR content led to improvements in the physical properties (D, WU, and TS), while negatively affecting the mechanical properties (MOR, MOE, IS, and HS) of the resulting panels. However, the addition of nano-SiO2 improved both the physical and mechanical properties (MOR, MOE, and HS) of the panels. Furthermore, it was observed that the mechanical properties were enhanced with increasing the number of beech layers, although the WU of panels decreased compared to panels made with alder and poplar. Overall, the improvement in the physical properties of the panels followed the order of the arrangement of rubber layers > nano-SiO2 content > veneer layers.

Adaptation of the Coniferous Forests to Natural Fire Disturbances in the Altai Mountains, Xinjiang, China

The Altai Mountains, located in the northwesternmost part of China, have a harsh climate and little human activity, making it an excellent location to study forest ecology undisturbed by human interference. The forest is frequently struck by lightning and experiences long-term natural fire disturbances, leading to the evolution of unique fire adaptation traits in the major conifer species. To explore the role of natural fire disturbances in the Altai Mountain forest ecosystem, we conducted a study on the fire adaptation traits of Larix sibirica, Pinus sibirica, Picea obovata, and Abies sibirica, and reconstructed the fire history of the forest area over the past 100 years. We investigated three representative forest areas with varying fire disturbance conditions and habitats in the Altai Mountains. Data on fire disturbance conditions, relative air humidity, and species composition were collected in these areas. Basal diameter to diameter at breast height, relative bark thickness, and under-crown heights were measured and counted for each of the four species, and litter, bark, and wood layers were sampled and analyzed for physicochemical properties (ash, fat, and higher heating value) for each of the four species in the plots examined. We conducted a count of the four conifer species in the forest for each fire adaptation index and analyzed the differences in fire adaptation traits among the species. Larix sibirica showed fire-tolerant traits, Pinus sibirica displayed fire-embracer traits, and Picea obovata and Abies sibirica exhibited fire-avoider traits. Through the analysis of stand composition and exposure to fire disturbance in the different forest areas, we were able to correlate the fire-adaptive strategies of the four conifers with stand characteristics under varying fire disturbances and habitats. The interaction between forests and fires, and their adaptation to each other, ultimately create the current ecosystems in the Altai Mountains.

Intenzitet toplinske modifikacije topolovine. Dio 1

Wood heat treatment is an environmentally friendly method, and the heat-treated wood properties are closely related to thermal modification intensity. This study focuses on the 0-3 mm surface layer (SL) of poplar wood heat treated at 160~220 °C. The modification intensity, including surface color, hardness, chemical component and morphological changes of the SL, was evaluated. The findings of this research showed that the color difference of the poplar wood before and after heat treatment (ΔE*1) increased; the color difference between up-surface and down-surface of the SL (ΔE*2) also increased with the treatment temperature. Consequently, the surface hardness (HR) decreased with the increase of treatment intensity. When the treatment temperature was higher than 160 °C, the up-surface and down-surface of the SL were statistically different in color. Chemical component analysis revealed that the heat treatment degrades wood components, especially the hemicellulose, and correlation analysis showed a significant correlation between the change rate of hemicellulose and the ΔE*1 or HR value; the prediction functions have been established at a high confidence level of 0.99. Overall, the thermal modification intensity of the heat-treated surface layer (SL) of poplar wood varies, and the HR and ΔE*1 value could be used to characterize and predict the modification intensity and degree of thermal degradation of the surface layer of heat-treated poplar wood.

CONSERVATION PROCESSES OF A WOODEN COFFIN COVERED WITH A BLACK RESIN LAYER AND COLORED MATERIALS IN DAHSHUR ARCHAEOLOGICAL AREA

This paper describes the results of a multi-technological analytical protocol performed on the painted surface of an Egyptian wooden coffin and documents the conservation processes of a wooden coffin covered with a black resin layer and coloured materials in Dahshur Archaeological Area dating back to the late period. It uses visual observation, optical microscopy (OM), technical imaging, 2D and 3D programmes, and a scan made using an electron microscope coupled with an Energy Dispersive X-ray (SEM-EDX), X-ray diffraction (XRD). Wood identification was also carried out. The results showed the use of yellow ochre for the yellow painted layer; the ground layer was calcium carbonate with gypsum, and the fabric layer was linen. The conservation processes of the wooden coffin included mechanical and chemical cleaning; reassembling the separated wooden parts, ground layer, and black resin layers; filling the edge of the ground layer; and consolidating the wood, black resin, and painted layer. The conservation processes included mechanical cleaning using soft brushes, chemical cleaning using xylene and distilled water for the black resin layer and ethyl alcohol and distilled water for the painted layer, stabilisation of the separated ground layer using Paraloid B72, filling the cracks of the ground layers using glass microballoons with Paraloid B72, and consolidating the painted layer with nano-silica with Klucel G (hydroxypropyl cellulose) (0.5% concentration).

Evaluation of the Quality of Wood Impregnation with Inorganic Fire Retardants During Autoclaving

The problem of determining the depth of impregnation of wood with an aqueous solution of sodium bicarbonate is considered. The relevance of the study is due to the need to develop a method of non-destructive testing of wood impregnated with flame retardants in order to identify industrial defects and (or) counterfeit products. The authors of the article propose a method for determining changes in the concentration of sodium bicarbonate in flushes from wood layers when impregnated with a nine percent solution of this salt under various conditions of treatment in an autoclave. In the work on determining the depth of impregnation with a nine percent sodium bicarbonate solution of wood during autoclave treatment, an experiment was conducted. Within the framework of this experiment, it was planned to confirm or refute the working hypothesis about the presence of anisotropy of wood by layer-by-layer examination of the depth of its impregnation with an aqueous solution of sodium bicarbonate in layers when they are obtained by sawing along and across the fibers. It was also planned to develop a methodology for conducting a study of samples of wood layers impregnated with a nine percent aqueous solution of sodium bicarbonate under various autoclaving conditions. It was also necessary to establish a pattern of changes in the concentration of sodium bicarbonate in flushes from wood layers with appropriate flame retardant treatment. The authors also planned to obtain equations to describe the dynamics of changes in the concentration of sodium bicarbonate in flushes from impregnated wood layers under various autoclaving conditions. The results of this experiment made it possible to obtain an equation of the dynamics of the change in the mass fraction of sodium bicarbonate in the flushing from the wood layer in the longitudinal section from the sample. The value of the coefficient of determination for the resulting equation is determined. When layer-by-layer examination of the depth of impregnation of wood with an aqueous solution of sodium bicarbonate, anisotropy was observed in the cuts of layers along and across the fibers.

Numerical simulation of a shock absorber used for protecting of casks for spent nuclear fuel

The preparation and implementation of nuclear facilities decommissioning is a complex of different activities strongly related to safety. After shut down of both reactor units in 2004 and 2005, it was designed of a new spent nuclear fuel (SNF) storage facility to the storage function envisages a separate place for handling of casks with SNF. The SNF handling operation itself induces some challenges for safety. One of such risks could be the dropping of Cask with SNF during its lifting operation. A special shock absorber was designed to avoid failure of fuel assemblies in case of hypothetical dropping of this Cask. This shock absorber consists of 14 fir wood layers and reinforced concrete slabs on the top. It is very important evaluate the interaction of these layers during dynamic impact. The dynamic impact characteristics of the cask under free-drop conditions should be investigated via the proposed numerical simulation method and to evaluate the reliability of the shock absorber during dynamic loading.The paper presents a dynamic analysis of the ability of shock absorbers to perform their safety functions considering the drop on them of different types of SNF casks. Numerical simulation was performed using Ansys computer code and the results were compared with analytical calculation results. The interaction and friction between wood layers was investigated via the proposed numerical simulation method. The results show that the fall of the container from a height of 3.2 m can be increased to 5 m, or the shock absorber performs its function when the weight of the SNF cask varies from 117 to 150 ton. The weight of the metallic and reinforced concrete casks used in Lithuania is between the estimated weight limits. That’s allows us to conclude that designed shock absorbers fulfil the assigned stopping function of the falling SNF casks.

The flexural behavior of cross laminated bamboo and timber (CLBT) and cross laminated timber (CLT) beams

The flexural behavior of cross laminated bamboo and timber (CLBT) and cross laminated timber (CLT) beams are studied to explore the potential of using glued laminated bamboo (glubam) in CLT panels to obtain similar or even better mechanical performance and other constructional and environmental merits. The 4-point bending experiments were conducted for full-scale model CLBT and CLT beams, assisted with using deformation instrumentations including the digital image correlation method (DICM) and conventional methods (LVDT and strain gauges). All the experimental results show that the CLBT beams have the similar even better bending stiffness and capacity than corresponding CLT beams, and the advantage is more significant for beams under in-plane bending condition. Analytical models based on two-dimensional (2D) elasticity theory are also applied to predict the flexural response of CLBT beams. The accuracy of the proposed analytical models can be verified by comparing the results with experimental results. Some parametric studies for CLBT beams with different combination configurations of glubam and wood layers are also conducted to provide several design suggestions to achieve favorite flexural performance for this type of cross laminated bamboo and timber beams.

FIRE RESISTANCE LIMITS OF WOOD DEPENDING ON IMPREGNATION TIME

Due to the high demand for wood as a building material, there are many ways to improve its strength, physical and other characteristics. One of the most important factors in the sphere of fire and industrial safety of facilities in which wood materials are used is the study of increasing the fire resistance of this material. The most effective ways to improve the fire protection of wood are surface treatment with fire-retardant paints and enamels, as well as impregnation of the inner layers of wood with special compounds. The purpose of the work is to study the impregnation of wood with Pirotex, to analyze the effect of the immersion time of wood in a fire retardant composition on burning behavior and afterglow time. In the course of the studies, the average values of the first flash, afterglow duration and the combustion initiation, depending on the time of impregnation, expressed in seconds, were established. Based on these data, it is possible to interpret the conclusion about the need for wood impregnation for a certain amount of time. The result of the experiments carried out is the establishment of the most effective range of wood impregnation time. Based on the results obtained, it was found that the most qualitative result is obtained by impregnation from 8 to 24 h at a temperature of 26 ± 1 °С.

Relationship between char depth of wood and cumulative heat exposure for fire investigation

Char depth can be a useful measurement to help fire investigators in their work, but the conclusions that can be drawn from it are still debated. While its use to highlight fire spread patterns is usually recognised, there is no consensus on its further interpretation to determine heat exposure or fire duration. The present paper aims at investigating the relationship between char depth and cumulative exposure (heat flux density integral over the exposure duration, in [MJ/m2]). A cone calorimeter was used to expose samples of four wood species (oak, beech, fir, and particleboard) to controlled heat fluxes for varying durations. This proved that, for a given cumulative exposure, the measured char depths are comparable, even if this cumulative exposure is obtained in very different ways. This quantitative analysis (e.g. predicting the cumulative exposure based on a char depth measurement) is an important addition to the typical qualitative use of char depth measurements (i.e. the estimation of fire spread direction). Moreover, the layer of wood that might have burned away, which is often difficult to estimate in the field, could be easily related to the char depth, making this type of measurement even more useable by fire investigators.

ЩОДО УДОСКОНАЛЕННЯ ДІЮЧИХ НОРМАТИВНИХ ДОКУМЕНТІВ ДЛЯ РОЗРАХУНКУ ЗГИНАЛЬНИХ ДЕРЕВ’ЯНИХ ЕЛЕМЕНТІВ ТА КОНСТРУКЦІЙ

The most common use of wood in construction is for bending elements. The calculation of bending members made of glued laminated timber requires the use of the section modulus of this member and the calculated values of the bending strength of the timber. The design bending strength of wood is determined based on the characteristic values obtained from the laws of elastic material under load. However, this statement completely contradicts the anisotropy of wood in its tensile and compressive behavior. If it is known that wood works 90-95% to failure in longitudinal tension, it is then it can be assumed that it is elastic at all. However, in longitudinal deformation, there is non-linear behavior with increasing elastic and plastic strains. Furthermore, the longitudinal tensile strength of wood is almost twice that of longitudinal compression. Therefore, even if the relative deformations in the wood are the same different compressive and tensile stresses arise in the bending element, i.e. . Many authors who have carried out experimental and theoretical studies on the performance of timber beams have pointed out that the neutral force line in the cross-section of the element in direct transverse bending, with increasing levels of single load, shifts towards the tensile zone. Therefore, using the moment of resistance of the cross section in the wooden element to determine the section modulus is incorrect. The moment of resistance of a section of a timber member is only determined if the centre of gravity of the section coincides with the centre of force line. Usually, the failure of long wooden beams ( ) in transverse bending usually occurs due to the fracture of the most stressed outer layers of wood in the of the tensile area and is brittle in nature. It is on such elements that the the temporary bending strength. It is on such elements that the bending strength is crucial. However, the values of , usually determined in the outermost wood layers of the tensile zone, based on the condition, only reach values of 70-75% of the longitudinal tensile strength of wood . It is not possible to determine the tensile strength of wood at this stress level. Therefore, the results of determining the bending strength of wood using the moment of resistance of the cross-section of a timber element determined in the limiting condition are erroneous due to the impossibility of establishing values

Mechanism elucidation for wood sandwich compression from the perspective of yield stress

Abstract To elucidate the mechanism of wood sandwich compression, the response of wood compressing yield stress to hygrothermal conditions was investigated in this study with respect to preheating temperature (30–210 °C) and moisture content (MC, 0–100 %). An associated functional model was developed to predict wood yield stress based on the measured MC and temperature in wood. A 1 % increase in wood MC or a 10 °C increase of temperature led to a decrease in wood yield stress exceeding 0.1 MPa. Significant variations in yield stress, exceeding 0.8 MPa, were observed between high MC layer(s) and the remaining layer(s) along the wood thickness when there was an MC variation over 5 %. Preheating the wood with by heating platens accelerated water/moisture migration in wood, resulting in relatively low yield stress in the wood interior areas where water/moisture had migrated. This study demonstrated that the comparatively low yield stress of some wood areas was responsible for sandwich compression. When mechanically compressed, only the wood layer(s) with lower yield stress was compressed, leading to sandwich compression, regardless of whether the mechanical force was applied tangentially or radially.

Nanomechanical/Micromechanical Approach to the Problems of Dendrochronology and Dendroclimatology

The most widespread approach in dendrochronology (wood dating) and dendroclimatology (climate reconstruction) is based on measurement of the width of annual growth rings by analyzing optical images of wood cross sections. This approach is quite efficient and easy to implement but it has inherent drawbacks. Raw data for these techniques originate from the optical properties of the wood surface, which are not directly related to other properties of wood, mechanical properties in particular. This paper describes a new quantitative approach applicable to dendrochronology and dendroclimatology based upon measurement of the micromechanical properties of wood by employing nanoindendation and digital sclerometry. It yields not only the width of annual growth rings and early and late wood layers with an accuracy not inferior to optical methods, but also rich data on the mechanical properties of the wood with a high spatial resolution that could be brought to subcellular scale if necessary. This data can be used for the dendrochronological analysis of archeological finds and the evaluation of climatic parameters during tree growth with a time resolution of up to a month or even better, which is unlike other common methods with a time resolution of one year. Moreover, the detailed continuous profiling of local mechanical properties can form a basis for improving our understanding of the nature and mechanisms of the formation of macromechanical properties important for applications and can clarify the climate factors that have the greatest impact on such properties.