Timber Density Research Articles

Correlation between thermal and density properties of chestnuts: preliminary results of experimental non-destructive testing

This study presents the preliminary outcomes of a methodology for the physical and mechanical characterization of various chestnut elements in different states of preservation. Strategizing conservation and retrofit interventions for timber is necessary, and to do this, it is necessary to establish an estimation of physical (transmissivity, thermal conductivity, humidity level, etc.) and mechanical properties (density, compressive or bending strength, etc.). This essential information is typically associated with timber defects, but there are lack of correlations. The primary objective is to establish correlations between thermal and density properties with the aim of preserving original assets. The investigation delves into the relationship between timber density and thermal properties through experimental non-destructive testing (NDT). Two NDTs were employed with the aim of correlating: penetrometric testing and active thermography investigations. The parametric study on the excitation period yielded valuable insights into the temporal dynamics of heat transfer within the timber, underscoring the significance of selecting appropriate excitation periods to capture precise thermal properties. Tabular data on relative humidity for salified, dried, and new samples provided a quantitative backdrop to these observations, unveiling the nuanced effects of humidity on the timber’s thermal response. The results of this study are positioned to inform future conservation efforts by laying the groundwork for a comprehensive understanding of timber’s mechanical properties. Particularly, the challenge lies in accurately estimating density, where surface tests are often less reliable than in-depth ones. Therefore, it is crucial to seek validation through other NDT tests, such as thermographic analysis and visual inspection, and hygrometric tests recognizing their importance in enhancing the reliability of density assessments. This approach will contribute to the development of more discerning preservation strategies.

Harvesting efficiency and understory damage with different cutting methods on two storied stands of silver birch and Norway spruce

Uneven-aged forests set certain challenges for cut-to-length harvesting work. It is a challenge to cost-effectively remove larger trees while leaving a healthy understory for regrowth. The study’s aim was to evaluate productivity and costs of harvesting two-storied Silver birch (Betula pendula Roth) and Norway spruce (Picea abies (L.) H. Karst.) stands by creating time consumption models for cutting, and using existing models for forwarding. Damage to the remaining understory spruce was also examined. Four different harvesting methods were used: 1) all dominant birches were cut; 2) half of them thinned and understory was preserved; compared to 3) normal thinning of birch stand without understory; and 4) clear cutting of two-storied stand. Results showed the time needed for birch cutting was 26–30% lower when the understory was not preserved. Pulpwood harvesting of small sized spruces that prevent birch cutting was expensive, especially because of forwarding of small amounts with low timber density on the strip roads. Generally, when taking the cutting and forwarding into account, the unit cost at clear cuttings was lowest, due to lesser limitations on work. It was noted that with increasing removal from 100 to 300 m3 ha–1, the relative share of initial undamaged spruces after the harvest decreased from 65 to 50% when the aim was to preserve them. During summertime harvesting, the amount of stem damage was bigger than during winter. In conclusion, two-storied stands are possible to transit to spruce stands by accepting some losses in harvesting productivity and damages on remaining trees.

Long-term effects of planting density and site quality on timber assortment structure based on a 41-year plantation trial of Chinese fir

Stand density control coupled with site control is a key technique for cultivating large-diameter timber of Chinese fir trees, whose yield can be effectively increased by the optimal density and site management mode employed. This study aimed to evaluate the dynamic changes in timber assortment structure under differing initial planting densities and site quality based on growth data of a 41-year trial of Chinese fir plantations. Our results showed that the total timber yield and both large-diameter timber outturn and the outturn rate all increased with better site quality under the same initial planting density. Further, the outturn peak as well as outturn rate peak for both medium- and small-diameter timber was reached sooner with improved site quality. For the same site class, a lower initial planting density augmented the total timber outturn rate, and also resulted in less time required for the total timber outturn rate to reach a constant or maximum value. Finally, the total timber outturn rate of all density plots tended to be nearly identical. Using a high planting density increased the outturn of small-diameter timber, whose outturn peak was delayed in the denser plots. The bolstering effect of low density upon the growth of large-diameter timber was enhanced by higher site quality, with density-induced differences in large-diameter timber more pronounced; conversely, that promoting effect weakened under poor site quality conditions. The interaction between planting density and site index significantly influenced the growth of any timber assortment of Chinese fir in the early stage following its formation. Notably, the significant effect of site index on large-diameter timber lasted longer than that of other timber assortments. The optimal site conditions for cultivating large-diameter timber trees of Chinese fir consist of a site class ≥ 20 with a planting density limited to no more than 1667 trees/ha, whose stand rotation period must be over 26 years, so as to maximize the output of large-diameter timber yield. Our empirical findings will be helpful for the construction of an optimal cultivation mode for the density, site, and rotation age of large-diameter timber in Chinese fir plantations.

Using Optimization Algorithms-Based ANN to Determine the Temperatures in Timber Exposed to Fire for a Long Duration

The article investigates the temperature prediction in rectangular timber cross-sections exposed to fire. Timber density, exposure time, and the point coordinates within the cross-section are treated as inputs to determine the temperatures. A total of 54,776 samples of wood cross-sections with a variety of characteristics were considered in this study. Of the sample data, 70% was dedicated to training the networks, while the remaining 30% was used for testing the networks. Feed-forward networks with various topologies were employed to examine the temperatures of timber exposed to fire for more than 1500 s. The weight of the artificial neural network was optimized using bat and genetic algorithms. The results conclude that both algorithms are efficient and accurate tools for determining the temperatures, with the bat algorithm being marginally superior in accuracy than the genetic algorithm.

Comparative Evaluation of Physical and Mechanical Properties in the Radial Positions of Coconut (Cocos nucifera) Timber

This study evaluated the variation of the physical and mechanical properties within coconut timber's radial position (dermal, sub-dermal, core). Properties were studied on the 55-year-old coconut palm from KAU coconut farm Vellanikkara, in Thrissur, district Kerala. The density of coconut timber at the radial positions was 862.3 kg m-3, 670.8 kg m-3 and 287.9 kg m-3, respectively, for the dermal, sub-dermal, and core positions. The average moisture content of coconut timber in the dermal, sub-dermal, and core positions was 15.7 %, 16.6 %, and 17.5 %, respectively. Compressive strength parallel to the grain at the three radial positions such as dermal, sub-dermal, and core is 32764.77 kg cm-2, 25591 kg cm-2, 7532.35 kg cm-2, respectively, and the compressive strength perpendicular to the grain was found as 46712.42 kg cm-2, 39233.3 kg cm-2, 22353.04 kg cm-2. Hardness measured at the side and ends of the dermal position is 1207.612 kg and 767.65 kg, respectively. In the sub-dermal position, 1035.7 kg and 750.88 kg, respectively. The core position is 252.34 kg and 359.31 kg, respectively.

Strength index-based timber classification of Sri Lankan timbers and potential for finger-joint production from wood off-cuts

ABSTRACT Shorter sections of sawn timber material resulted from timber industry are considered to be wastes; thus regularly dumped by sawmills. Finger-joint, a method which connects two small pieces of timber together is recognized as a sound technique to minimize the wastage. In this process, sections of different timber species are bonded together for making finger-joint boards. In this connection, selection of the best possible combination of timber species is vital as the success largely depends on the mechanical properties of the pieces. In this study, commonly used 32 timber species were employed to develop a timber classification system based on strength properties of timber species. Cluster analysis was used in grouping the species with similar strength properties. Accordingly, timber species were grouped into five strength classes as very low, low, medium, high and very high. A significant correlation (P = 0.000) between the strength index and timber density was also observed.

Embedment Strength of Low- and Medium-Density Hardwood Species from Spain

The embedment strength is a key parameter in the design of timber connections with metal fasteners. This property can be determined by the equations given by design codes such as the Eurocode 5, which are based on the European Yield Model proposed by Johansen, and it depends on the value of timber density among other parameters. These equations provided by design codes are based on experimental tests performed mainly in softwood species; thus, the objective of this work is to evaluate the embedment strength of two low- and medium-density hardwood species from Spain (poplar—Populus x euroamericana; beech—Fagus sylvatica) in the parallel and perpendicular to grain directions. Four different experimental test configurations were carried out according to EN 383 for each species using two different fasteners: (i) a 9 mm-diameter screw and (ii) a 12 mm-diameter bolt. Results of embedment strength were evaluated according to three different determination methods, and later compared with the current equations provided by Eurocode 5 (EC5) and new ones proposed in the draft of the new Eurocode 5 (prEC5). Results showed that current equations overestimated perpendicular to grain embedment strength for the cases studied, while the equation proposed in prEC5 for screws fitted best perpendicular to grain embedment strength. However, it underestimated the parallel to grain one because it does not consider any difference due to load-to-grain angle (α). Finally, ratios between experimental parallel and perpendicular to grain embedment strength were studied (k90), showing 30% and 44% higher values than the theoretical values resulting from k90 equations of EC5 and prEC5 for beech with screws and bolts, respectively, and 4% and 49% higher than the theoretical values for poplar with screws and bolts, respectively.

Half hole and full hole dowel embedment Strength: A review of international developments and recommendations for Australian softwoods

Embedment strength is an essential system property of the European Yield Model which is commonly used to predict the ductile capacity of timber joints using dowel-type fasteners. This paper presents a comprehensive review of international embedment test methods and prediction formulae in design codes and literature, as well as an experimental study to evaluate the impact of different test methods parallel to the grain. A total of 224 full hole (FH) tension and half hole (HH) compression tests were conducted according to AS/NZS ISO 10984.2 on Australian sawn softwoods (Radiata Pine and Southern Pine) to compare embedment strength resulting from FH specimens sized to EN 383 and HH specimens sized to ASTM D5764, respectively. The results were compared to dowel embedment strength formulae from literature, those contained in Eurocode 5, the National Design Specification (NDS) for Wood Construction, and the respective joint group strength values contained in AS 1720.1, which are based on empirical test data. It was found that all strength prediction models were non-conservative except for a formula proposed by Smith et al. in 2004, which was based on FH tension tests in Australian Radiata Pine and Slash Pine. Furthermore, a strong correlation between timber density and embedment strength was found for both test methods, however, only FH tests displayed a correlation between dowel diameter and embedment strength, which is consistent with the embedment strengths formulae currently contained in Eurocode 5 and the NDS.

РОЗВИТОК ЕМОЦІЙНОЇ СТІЙКОСТІ МАЙБУТНЬОГО ВЧИТЕЛЯ МУЗИЧНОГО МИСТЕЦТВА В КЛАСІ ВОКАЛУ

The author of the article reveals the problem of developing the emotional stability of future music art teachers in high school. It has been determined that the specified problem is relevant for the profession of a musician, which requires endurance both while learning musical pieces and when performing them in public. Analyzing the source base, the author defines the concept of "emotional stability" as a component of emotional intelligence, which is a personality quality, formed in conditions of extreme activities. It implements through emotional intellect of a personality and provides a person's ability to succeed, withstand significant intellectual, volitional and emotional stress, and at the same time to maintain the state of psychophysical balance. According to V. Dryndin's research, the following factors determine the state of a musician's stiffness: lack of a performer’s mental mobilization skills; insufficient formation for public performances; the influence of high personal anxiety and, as a consequence, reduced emotional stability; uncertainty if the performance program is memorized by heart well enough; the effect of a fixed reflex to the inevitable fright before the performance and its negative impact on performance; targeting of the internal attitude at self-esteem of one's own personality instead of performing a piece in the required manner; lack of self-regulation skills (the presence of shyness, inability to manage one’s own emotional state); awareness of manifestation of negative emotions (hand tremors, palpitations, sweating, sluggishness or tension of a performer’s apparatus, etc.). That is why, development of self-control will help to regulate the mental state of a musician and create a musical image under the control of his or her consciousness. Also in the process of training a vocalist for public performance it is important to learn the language of emotions and the ability to be emotionally expressive in speech and singing. Emotions in singing affect the density and brightness of voice timber, vocal position, resonance, nuance and kind of singing vibrato, semantic intonation, activity of articulatory organs and the way of sound production. Therefore, each emotional state of a performer is embodied in the unity of a complex of acoustic features and effective expressiveness. Thus, the professional becoming of a future musician in the process of vocal training is impossible without the engaging of emotional sphere and developing a high level of emotional stability, since emotional experiences while performing musical pieces affect the psychophysiological state of a musician.

Efficiency of Visual and Machine Strength Grading of Sawn Timber with Respect to Log Type

A batch of pine timber sawn from butt, middle and top logs was strength graded with the visual method (classification into grading classes KW—best quality, KS—medium quality, KG—inferior quality and Reject) and with the machine strength grading method—performed with the use of a mobile timber grader (classification into C strength classes). We compared the efficiency of grading classes and strength classes, depending on the type of log from which the material was obtained (butt, middle, top). Next, a strength grading machine was used to measure the modulus of elasticity in bending (MOE) and static bending strength (MOR). The ANOVA confirmed the influence of both the log type (butt, middle, top), the C strength class, and the visual strength grading class on the values of density (DEN) and MOR. Timber density and MOR decreased from the butt log section to the top log section. The ANOVA confirmed the influence of log type on MOE values, but only to a limited extent.

Timber encasement of steel structures as an alternative fire insulation

AbstractThis paper presents the results of an investigation on the thermal behaviour of fire‐exposed steel profiles embedded in timber elements.Several tests were performed on small unloaded specimens in a small furnace. The different specimens were made of bare steel profiles, timber elements or steel‐timber hybrid members. Different welded I or T steel sections and wood species were used. The specimens were set horizontally (3‐side exposure) or vertically (4‐side exposure) in the furnace and heated using a couple of burners. The temperatures of the steel profiles were measured by welded K thermocouples.The results from this experimental campaign, in terms of temperature of the furnace and of the specimens, density and moisture content of timber, were then used to calibrate a heat transfer model under Ansys finite element code. This 2D numerical model is mainly based on the behaviour laws of structural steel and timber from Eurocodes 3 and 5 respectively. Regarding the specific heat of timber, several relationships were applied. A comparative analysis of experimental and numerical results confirms the fire insulation brought to steel by timber. It also highlights the ability of the model to simulate the thermal behaviour of both steel and timber, in terms of heating and charring rates.

Timber-to-timber and steel-to-timber screw connections: Derivation of the slip modulus via beam on elastic foundation model

The aim of this paper is to propose formulations for the slip modulus prediction of timber-to-timber connections (TTC) and steel-to-timber connections (STC) with inclined screws and possible interlayers. The beam on elastic foundation model, previously developed for timber-to-concrete connections, was extended to consider the flexibility of both media where the screw is inserted. Since a significant influence of the fastener diameter on the foundation modulus was observed in tests, an interpolating formula correlating the foundation modulus with timber density and the fastener diameter was derived. The exact solution of the timber-to-timber analytical model was found to agree well with experimental results for total and double thread screws. A parametric study was undertaken to prove that connections with inclined screws have significantly higher slip modulus and lower degradation of performance as the diameter decreases or the thickness of the intermediate layer increases compared to connections with screws perpendicular to the sliding plane. Furthermore, the slip modulus of inclined screws was found to be limited by the weakest timber layer. Closed form expressions for the prediction of the slip modulus were derived by interpolation for the most important cases of technical interest. These formulas can be proposed for the implementations in codes of practice such as the Eurocode 5, since simplified formulas of the slip modulus are currently missing for connections with inclined fasteners and interlayers.

Comparison of Physical and Mechanical Properties of Beech and Walnut Wood from Iran and Georgian Beech

Beech (Fagus orientalis Lipsky) forests in Iran are one of the most important sources of the hardwood species used for lumber, furniture, and interior object design due to its hardness, wear resistance, strength, and excellent bending capabilities. Furthermore, Iran is third most important country for walnut wood production after China and United States. Therefore, in this study, we compared specific mechanical properties between beech wood obtained from Sangdeh (Iran) and Georgia and four different kinds of walnut woods in Iran. Physical and mechanical tests were performed according to ISO 3129 (2012) and ASTM (D143-14) standards. The moisture content of all samples was 12% during mechanical tests. The mean dry density of Sangdeh and Georgian beech obtained was 0.61 and 0.65 g/cm3, respectively, while the mean dry density of Noor, Shahrekord, Mashhad, and Mako walnut woods measured 0.62, 0.59, 0.62, and 0.57 g/cm3, respectively. The results showed significant differences among the properties of the Sangdeh and Georgian species and the four different walnut tree woods. Overall, the obtained strengths of Georgian timber were higher than that of the Iranian beech, which was attributed to the higher density of Georgian timber. Furthermore, due to the higher density of the walnut species in the Noor and Mashhad regions, the measured mechanical strengths of these trees were higher than those of other walnut species. The obtained results provide relevant information to determinate the future applications of each wood source.

The Influence of Scots Pine Log Type (Pinus sylvestris L.) on the Mechanical Properties of Lumber

The paper presents an analysis of the influence of geographical origin and Scots pine log type on the mechanical properties of the timber sawn from them. The tested timber was sawn from logs obtained from three different forestry regions in Poland, located in the western part of the country. A batch of 150 timber pieces was obtained from each region. The cross-section had the dimensions of 40 mm × 138 mm. The timber was sawn from logs of three different types: butt, middle and top, from a fresh, mixed forest around 120 years old. The timber was dried in industrial conditions and planed four times. The values determined for the timber under research were the static modulus of elasticity in bending (MOE), and the bending strength (MOR). Moreover, timber density (DEN) was determined with the stereometric method. For all three sites, the highest average values of the tested timber properties were obtained for timber made of butt logs, and the lowest for timber made of top logs. It was concluded that the tested Scots pine properties depended on the type of log, and to limited extent, on its geographic origin. The statistical analysis revealed that the geographic origin of the logs that the tested timber was made of had a statistically significant impact on the variance of all the tested timber properties. The type of log also had a statistically significant influence on the variance of all the tested properties.

Biological and economic features of the ‘Voronezh Giant’ hybrid poplar

The purpose of this publication is to generalize the available experimental data on the survival, growth, stability, technical and other characteristics of this hybrid and to clarify proposals for its practical use. Long-term studies have been carried out on the five variety testing sites in various soil and climatic zones of the South-Eastern part of Russia and in Ukraine. The survival rate of this poplar were quite high (from 75 to 96%), on average 81%. The age of economic exploitability in the forest-steppe zone with a 20 m2 feeding area per tree was equal to 29 years. To this age the ‘Voronezh Giant’ accumulated stem wood stock of 550-640 m3/ha. The duration of shoot growth was 146 days, and the growing season was 177 days. It was distinguished by high winter hardiness, relative drought resistance, wind resistance, low damage by primary and secondary entomopests, and affection with phytodiseases, but a low straight trunk. It has a fairly high timber density, the length of the wood fiber and the cellulose content, which is important for the pulp and paper industry. The freshly picked green leaves of this poplar are close to the nutritional value of meadow herbs and lucerne. In general, the poplar ‘Voronezh Giant’ is promising for growing wood pulp, introducing into energy, shelter-belts, roadsides, riversides and other reclamation plantings. Given into account its male gender and high decorativeness, it can be also recommended in the greenery landscaping.

DENSITY EFFECTS AND ITS RELATIONSHIP WITH MAJOR FLAME CHARACTERISTICS OF SELECTED FIRE TOLERANT TREES IN SOUTH-EAST NIGERIA: A LOOK AT OVEN AND SUN DRIED TIMBERS

Physical and flame characteristics of fifteen tree species in South-East Nigeria were investigated. The tree species Daniellia oliveri, Anacadium occidentale, Vitex doniana, Lonchocarpus griffonianus, Gmelina arborea, Nauclea latifolia, Tectona grandis, Mangifera indica, Delonix regia, Newbouldia laevis, Azadirachta indica, Dialium guineense, Terminalia superba, Manilkara obovata and Irvingia gabonensis were identified and named by taxonomists. The aim was to investigate the effects of oven and sun dried densities of timbers on major flame characteristics (ignition time, flame propagation rate, after glow time, flame duration and ash formation) and to establish timber density relationship with the flame properties. Physical properties (density and moisture content) and flame characteristics of all the timbers were carried out using their respective standard methods. Oven and sun dried densities of timbers ranged from 0.39 to 0.97 and 0.45 to 1.16 g/cm3 respectively. Moisture content of oven and sun dried timbers ranged from 8.02 to 11.56% and 8.15 to 11.65 % respectively. The range of values for ignition time were (3.00-10.00) seconds for oven dried timbers and (5.00-10.00) seconds for sun dried timbers. Flame propagation rate ranged between 0.15 and 0.27 cm/s and from 0.09 to 0.25 cm/s for oven and sun dried timbers respectively. The values for flame duration ranged from 12.00 to 56.00 seconds for oven dried timbers and 7.00 to 45.00 seconds for sun dried timbers. Afterglow times of oven and sun dried timbers ranged from 70.00 to 267.00 and 19.00 to 188.00 seconds respectively. Ash formation values ranged from 0.19 to 2.38 and 0.25 to 2.46 % for oven and sun dried timbers respectively. Combustion/pyrolysis pattern of oven and sun dried timbers on exposure to fire was similar. Density related to flame propagation rate, although, for the denser hard woods above 0.60g/cm3 and 0.70g/cm3 for oven and sun dried timbers respectively, this dependence was less straight forward. The flame characteristics of the oven dried timbers compared favourably with sun dried timbers and showed that ignition time, flame duration, afterglow time and ash formation have no clear relationship with timber density.

Classificação visual e mecânica da espécie <i>Cryptomeria japonica</i> D. Don para utilização em madeira laminada colada

O objetivo foi avaliar as propriedades mecânicas da madeira, a influência da classificação visual de lâminas de Cryptomeria japonica D. Don no desempenho mecânico para uso em elementos estruturais em MLC, comparando com os requisitos mínimos exigidos pelas normas brasileira ABNT NBR 7190 (1997) e europeia EN 338 (2016). Os ensaios para caracterização física e mecânica da madeira sólida seguiram as recomendações das normas COPANT 461 (1972), 464 (1972) e 555 (1973) para densidade básica, resistência à compressão paralela às fibras e resistência à flexão estática, respectivamente; e ABNT NBR 7190 (1997) para resistência ao cisalhamento. As 80 lâminas de madeira foram produzidas com dimensões de 6,0 x 1,5 x 220,0 cm (largura x espessura x comprimento) e posteriormente classificadas visualmente conforme a norma americana ASTM D245 (2006) e pelo módulo de elasticidade - EW (ASTM D4761 (2013)). Ao todo, 20 vigas de MLC foram confeccionadas, sendo estas formadas pela combinação das lâminas classificadas nas classes visuais: Testemunha (lâminas limpas, ou seja, sem defeitos), T1 (limpas e estrutural especial - SE), T2 (S1, S2, S3) e T3 (limpas, SE, S1, S2, S3), as vigas foram avaliadas em testes mecânicos de resistência à flexão estática e resistências à tração normal às fibras e cisalhamento para linha de cola. Os resultados indicaram que como madeira sólida a espécie não apresentou resistência mínima para que seja classificada como C-20 pela ABNT NBR 7190 (1997), entretanto a espécie foi classificada como classe estrutural C-16 pela norma EN 338. As vigas de MLC apresentaram valores dentro do mínimo exigido para a classe C-20, conforme a ABNT NBR 7190 (1997). A utilização de lâminas com nós classificados visualmente não diminuiu a resistência das vigas de MLC quando comparado com vigas produzidas com lâminas sem nós.

Correlation between the share of latewood and the density of sawn timber from the Silesian Forestry Region

Correlation between the share of latewood and the density of sawn timber from the Silesian Forestry Region. The paper describes the results of density measurements and the share of latewood in pine wood samples (Pinus sylvestris L.) from the Silesian Forestry Region in Poland. The samples were obtained from sawn timber from different kinds of log: butt, middle and top. The place from which the timber was obtained (three different log kinds) was taken into account when assessing the correlation between wood density and the share of latewood.

Wood Density Determination by Drilling Chips Extraction in Ten Softwood and Hardwood Species

Research Highlights: The novelty of this study is the development of an accurate wood density estimation method based on a relatively brand new semi-destructive testing technique (drilling chips extraction). This method is especially crucial in the assessment of existing timber structures. Background and Objectives: Probing, drilling, and coring are non-destructive and semi-destructive techniques commonly used for timber density estimation in existing timber structures. Most of these techniques show poor or medium accuracy or are so expensive or destructive. This paper aims to obtain accurate estimation models for wood density in existing structures using the easy to use drilling chips extraction technique. Materials and Methods: 300 specimens (95 × 65 × 200 mm3) from ten softwood and hardwood species covering a wide range of density (from 350 to 980 kg·m−3) were tested after conditioning. The Wood Extractor device based on the drilling chips extraction technique was used in the radial and the tangential direction. Mass of the chips collected (drilling residue) from each drill was recorded. Results: Density obtained from drilling residue was not statistically significantly different between radial and tangential directions avoiding take into account direction when measuring. The density obtained in the whole specimens is slightly higher than the density obtained by drilling residue being this difference uniformly through the range of densities studied. Two different estimation models were presented with high determination coefficients (96% and 97%) and low standard errors. These results were similar to those obtained by other authors using core drilling but causing less damage. Conclusions: Drilling chips extractor is a simple, reliable and inexpensive method to estimate density in existing structures with accuracy.

Classification of Finger Joint Timber Based on Strength Index

At present, off-cut wood pieces are dumped by sawmills as they are considered to be wastes in the wood industry. Inadequate length of sawn timber material is also reported to be a limiting factor for fully utilization of timbers. Finger joint, a method which connects two small pieces of timber together is identified as a sound technique to minimize the wastage. As there is no classification system applicable for finger joint timber in Sri Lanka, the present study focused on developing a classification system for selected 32 timber species based on their strength properties. The relationship between the strength properties and density of selected timber species was also investigated. Strength properties of finger jointed timber species were evaluated by three-point bending and compression tests according to BS 373:1957 using Universal Testing Machine (UTM-100).Factors were identified through an analysis to determine the strength index for the selected samples. The strength index values were grouped into five strength classes as very low, low, medium, high and very high. Cluster analysis was used in grouping the species with similar strength properties. Regression analysis was performed to identify the strength index of compression parallel to grain, compression perpendicular to grain, modulus of elasticity and modulus of rupture varies on density. A significant correlation (p=0.05) between the strength index and timber density was observed. Keywords: Finger joint, timber classification, universal testing machine, strengthindex