Strength Parallel Research Articles

Reliability Studies on Timber Data from Nigerian Grown Iroko Tree (<i>Chlorophora excelsa</i>) as Bridge Beam Material

This paper provides the results of structural reliability analysis carried out on the data of Nigerian grown Iroko tree (Chlorophora excelsa), to ascertain its structural performance as timber bridge beams. Five pieces of 50mm x 75mm x 3600mm of Nigerian grown Iroko hardwood were bought, seasoned naturally and 200 pieces of samples were prepared for determination of their strength properties, (which include bending strength parallel to grain, tensile strength parallel to grain, compressive strength parallel to grain, compressive strength perpendicular to grain and shear strength parallel to grain) at a moisture content of 18%, in accordance with the British Standard BS 373 of 1957. Statistical analysis was carried out using the strength properties for determination of mean, standard deviation, coefficient of variations, confidence limits and Chi-Square goodness of fits. Structural analysis and design of a timber bridge beam using the determined data from the Nigerian grown Iroko timber, in accordance with BS 5268 were carried out under the Ultimate Limit State of loading (ULSL). Reliability analysis was carried out to ascertain its level of safety using First-Order Reliability Method (FORM). Sensitivity analysis was also carried out by varying the depth of beam, imposed live load, breadth of the beam, unit weight of the Iroko timber, span of the beam as well as the end bearing length. The result revealed that the Nigerian grown Iroko timber is a satisfactory structural material for timber bridge beams at depth of 400mm, breadth of 150mm and span of 5000mm under the ULSL. The probabilities of failure of the Nigerian grown Iroko timber bridge beam in bending, shear, compression and deflection are respectively, under the specified conditions of loading.

Assessment of certain wood quality parameters of selected genotypes of Melia dubia Cav. grown in a seedling seed orchard

Certain wood quality parameters of about 9-year-old Melia dubia Cav. trees grown in a seedling seed orchard at Yeshwanthpura Research Station of Kolar research range, Karnataka India were studied. Trees were categorized into three classes depending upon their girth at the breast height––small ( 60 cm). Different anatomical (gross structure), physical and mechanical properties of the wood were evaluated using standard testing procedures and Indian Standards. The results of this study showed that there was no significant difference in the heartwood percentage and specific gravity among three girth classes. High shrinkage values from green to oven-dry condition in all the classes indicate that the timber is dimensionally unstable compared to teak. The static bending strength parameters––FS at LP, MOR and MOE, compression strength parallel to grain, compressive strength perpendicular to grain at limit of proportionality and surface hardness (side and end) were evaluated and compared among all the three girth classes. The data on mechanical properties were statistically analysed using ANOVA between three girth classes. The results on wood quality parameters may be utilized in selection of suitable genotypes for raising large scale plantations.

Probabilistic Models for Structural Performance of Rounded Dovetail Joints

AbstractThis paper presents probabilistic models for the structural performance of rounded dovetail joints. The models are developed with a Bayesian technique, which implies that the model uncertainty is explicitly characterized by random variables. The Bayesian approach also promotes model updating when new test results become available in the future. Practical insight is gained from the modeling process, which includes a novel search for influential parameters, and from the subsequent probabilistic analysis with the models. The models are based on 80 tests of single and double dovetail joints with varying geometric parameters, specifically the flange angle and the dovetail height. A significant effort was made to record variables that conceivably influence the performance of this type of joint, including a series of material parameters: tension strength perpendicular to grain, shear strength parallel to grain, moisture content, density, growth ring density, and growth ring orientation. This paper explor...

Strength properties and effect of moisture content on the bending and compressive strength parallel to the grain of sugi (Cryptomeria japonica) round timber

Static bending tests and compressive test parallel to the grain of sugi (Japanese cedar, Cryptomeria japonica) green round timber were conducted to confirm whether its strength would satisfy the referenced strength determined by the Construction Ministry. The strength of green round timber and air-dried round timber were compared for bending and compression parallel to the grain. The strength change ratio in response to a 1 % change in the moisture content of round timber was compared with that of small clear specimens and timber. The results revealed that a 5 % parametric tolerance limit of bending and compressive strength parallel to the grain satisfied the referenced strength, even when using green round timber. The average strength of air-dried round timber was higher than that of green round timber, in both bending and compression parallel to the grain, with significant differences indicated at a 5 % significance level. The relation between the cross-section area that includes round timber, timber and the small clear specimens, and the strength change ratio in response to a 1 % change in moisture content change was fitted to a logarithm curve. Thus, the size of the specimen was considered to affect the strength change ratio.

EFFECT OF THERMAL TREATMENT WITH METHYLOLUREA IMPREGNATED ON POPLAR WOOD

The aim of this research was to study the physical and chemical performance of poplar wood treated by chemi-thermal modification. A thermal treatment was used to catalyze the effect of the methylolurea impregnated pre-treatment by curing the poplar wood at 160 °C under atmospheric conditions. The results showed that the thermal treatment played an important role in the chemical and mechanical performance. Such an approach not only can significantly reduce the hygroscopicity, but also can increase the bending strength and compressive strength parallel to grain. The positions of the XRD peaks did not change, which indicated that the structure of cellulose was not noticeably affected by the thermal treatment. The FT-IR analysis showed that the intensity of hydroxyl and carbonyl absorption peaks decreased significantly, which indicated that the NH-CH2-OH of methylolurea reacted with the wood carboxyl (C=O) and hydroxyl (-OH). The TGA showed that the thermal stability of treated wood improved. The SEM showed that the cell wall and vessels were filled with impregnated chemicals.

Impact of Kiln Drying Schedule upon Some Mechanical Properties of Poplar Wood

In the present research, the effect of three kiln drying schedules of T5-D2, T5-D4, and T5-D6 on poplar wood mechanical properties was investigated. The lumber was dried in a convectional laboratory kiln and then the compression strength in a parallel and perpendicular direction toward the grain, hardness, and nail withdrawal resistance were evaluated. The obtained results indicated with change from schedule T5-D2 to T5-D4, compression strength whether parallel or perpendicular to grain, hardness in tangential, radial, and transverse surfaces as well as, nail withdrawal resistance in tangential, radial, and transverse surfaces increased up to 18.1, 7.1, 16.4, 19.7, 14.1, 19.8, 5.7, and 9.2 % respectively, as against schedule T5-D2. Despite T5-D4 schedule, compression strength parallel to grain dropped in specimens dried by schedule T5-D6. However, nail withdrawal resistance of specimens dried by T5-D6 schedule was higher in all the three surfaces than the two other schedules. As regards, the T5-D6 schedule, compression strength perpendicular to grain and also hardness in all the three surfaces rose as opposed to that of T5-D2 schedule, but showed a decrease in comparison to the corresponding figure in T5-D4. Moreover, statistical analysis revealed that except the compression strength perpendicular to grain, other mechanical strength inducing by various wood drying conditions were put in separate statistical groups.

SENSITIVITY OF SEVERAL SELECTED MECHANICAL PROPERTIES OF MOSO BAMBOO TO MOISTURE CONTENT CHANGE UNDER THE FIBRE SATURATION POINT

The moisture dependence of different mechanical properties of bamboo has not been fully understood. In this work, the longitudinal tensile modulus, bending modulus, and compressive and shearing strength parallel to the grain were determined for bamboo of ages 0.5, 1.5, 2.5, and 4.5 years under different moisture contents (MC) to elucidate the sensitivity of different mechanical properties of bamboo to MC change. The results showed that the four mechanical properties of bamboo respond differently to MC changes. Compressive and shearing strength parallel to the grain were most sensitive to MC changes, followed by longitudinal tensile modulus, then bending modulus. This can be partially explained by the different responses of the three main components in the plant cell wall to MC change. For tensile modulus and bending modulus, the effect of bamboo age on the sensitivity to MC change was insignificant, while young bamboo (0.5 years old) was more sensitive to MC changes for shear strength and less sensitive for compression strength than older bamboo.

THE EFFECT OF SPECIFIC GRAVITY ON EMBEDDING STRENGTH OF GLUEDLAMINATED(GLULAM) BAMBOO: NUMERICAL ANALYSIS AND EXPERIMENT

Glue-laminated (glulam) bamboo potentially used to be a substitute for wood as a building material, because it can be produced within four to five years of planting. Mechanical properties of glulam bamboo should be well understood by support the wider application of this new material in structural components. This study focused on embedding strength evaluation of glulam bamboo, were required to evaluate lateral resistance of dowel-type joints. The evaluation was carried out using experiment according to ASTM D5764 and numerical analysis performed with ADINATM. Material were considered in the experiment consist of bolt 12.2 mm diameter, a range of specific gravity of glulam bamboo from 0.57 to 0.79 and moisture contents varies from 11.14% to 12.45% were considered in the experiment. There were three groups of specimens: group A parallel loading to grain radial; group B parallel loading to grain tangential; and the last was group C perpendicular loading to grain. Glulam bamboo were modeled as an orthotropic nonlinear material whiles the dowel was assumed as perfectly rigid material. Contact condition between dowel and laminated bamboo was considered and the numerical model was solved under the plane stress assumption with deformation control. The experimental result was indicated that embedding strength parallel to grain (group A and B), it was significantly higher than group C. This phenomenon was apparent in the numerical study as well. The embedding strength of laminated bamboo (Fe) could be well predicted as 78.4G for parallel to grain radial, 72.79G for parallel to grain tangential; and 69.96G for perpendicular to grain radial, where G is the specific gravity.

PEMANFAATAN KAYU AKASIA MANGIUM (Acacia mangium Willd) UNTUK MEBEL

Timber Acacia mangium (Acacia mangium, Willd) for Furniture. The study aims to determine the mechanical and physical properties and the decorative value (color and fiber) wood of acacia mangium with using finishing materials. This type of finishing material used is ultran lasur natural dof ,ultran lasur classic teak, aqua politur clear dof, aqua politur akasia dan aqua politur cherry. After finishing the wood is stored for 3 months. Test parameters were observed, namely, physical and mechanical properties of wood, adhesion of finishing materials, color and appearance of the fiber, and timber dimensions expansion. The results showed that the mechanical physical properties of acacia wood qualified SNI. 01-0608-89 about the physical and mechanical properties of wood for furniture, air dry the moisture content from 13.78 to 14.89%, flexural strength from 509.25 to 680.50 kg/cm2, and compressive strength parallel to fiber 342.1 - 412.9 kg/cm2. Finishing the treatment process using five types of finishing materials can increase the decorative value (color and fiber) wood. Before finishing the process of acacia mangium wood has the appearance of colors and fibers and less attractive (scale scores 2-3), after finishing acacia wood fibers have the appearance of colors and interesting and very interesting (scale 4-5).Keywords: mangium wood, mechanical properties, decorative value, finishing, furniture.

Mechanical properties of thermally modified beech timber for structural purposes

The use of thermally modified timber for structural purposes is of increasing interest. In order to guarantee sufficient reliability in terms of load bearing capacity and fitness for use the strength and stiffness properties of this modified wood have to be assessed. Industrially produced, thermally modified structural timber members made of beech (Fagus sylvatica L.) were subject of the tests presented in this paper. Bending, tension parallel and perpendicular to grain and compression parallel and perpendicular to grain properties were determined. The derived mechanical properties were benchmarked to the European EN 338 strength class system for structural timber. It turned out that the used strong thermal treatment of the raw material resulted in a significant reduction of most of the strength properties. However, stiffness properties were not affected. In particular the strength properties perpendicular to grain suffered a lot due to the thermal modification whereas compression strength parallel to grain was unchanged. The main drawbacks found along the experiments were a pronounced brittle behaviour of the specimens and big variations in strength. For the determination of strength values it is proposed not to use correlations as provided in European standards but to test and state these properties discretely. On the basis of these results a general use of strongly thermally modified beech as structural timber cannot be recommended. However, for selected purposes, like e.g., for structural facade elements or for columns, the use of this material might be an option.

Effect of Combined Microwave Heating and Impinging Hot-Air on Rubberwood Drying

Applying microwave heating and impinging hot-air is one of the most interesting methods to increase the higher drying rates of rubberwood drying based on acceptable quality. A maximum microwave power level of 200W at a frequency of 2.45GHz with maximum working temperature of 70°C, only hotair (70°C) and combined microwave (200W) - hotair (70°C) were choosed to evaluate the effect of rubberwood drying by different width sizes (1, 2, 3 and 4 in.) by 46 in. length by 1 in. thick. In all cases, the drying time is reduced significantly from 168 h to less than 8-15 h in various wood widths and resulted in saving to an extent of about 91% of drying time from initial moisture content ranges of 73%-49% to 15% percent of moisture level. Drying stresses from prong test no found during drying and total color of rubberwood changed after high temperature drying is a natural surface when compared to fresh wood. The values of six strength compared to the reference values are concentrated in the ranges of 16.9-23.9 (11.0)MPa for shearing strength parallel to grain, 4291.1-6701.6 (4350)N for hardness, 73.3-110.2 (66.0)MPa for MOR, 7059.5-12856.7 (9240.0) MPa for MOE, 27.2-14.3 (5.0)MPa for compressive strength perpendicular to grain and 60.6-35.7 (32.0)MPa for compression strength parallel to grain. These results show that it is possible to develop a drying process for rubberwood using microwave-hot air in investigating further in this area.

Mechanical properties and wood structure characteristics of 35-year old home-garden teak from wet and dry localities of Kerala, India in comparison with plantation teak

Mechanical properties of teak wood grown in home-garden forestry and the anatomical factors influencing timber strength were investigated in comparison with that of a typical forest plantation. No significant differences were observed in modulus of elasticity and modulus of rupture with respect to wet, dry and plantation sites and the values are moderate compared with the standard teak. Where as, dry site home-garden teak exhibited higher compressive strength (MCS) parallel to grain (60.6 N/mm2) and differed significantly between wet and plantation sites (P ≤ 0.05). The higher MCS value was correlated with higher air-dry density (691 kg/m3) recorded coupled with thick fibre wall and smaller fibre lumen as elucidated by anatomical study. The microfibrillar angle also showed non-significant difference between the three localities (P = 0.05) and the value 12.5° was quite small to affect the timber strength adversely in its utilisation potential. The results of the present study revealed that farmer’s choice to fell homestead teak at short-rotation of 35-years is in no way affect the wood quality attributes such as density and strength.

Variation of Tensile Strength Parallel to the Fiber of Bamboo<i> Guadua Angustifolia Kunth</i> in Function of Moisture Content

As other natural materials used in construction, Bamboo Guadua is affected by different factors that can modify its strength. One factor is the equilibrium moisture content, which is a physical property related to temperature and relative humidity of the area where the material is used. Several studies have shown that the material strength to different load requirements decreases as moisture content increases. Samples from three different regions of the Republic of Colombia (Coffee region, Valle del Cauca and Cundinamarca) were taken to study the variation of the tensile strength parallel to the fiber of bamboo Guadua Angustifolia Kunth in function of the moisture content. Ten culms were taken from each region and three sections from different parts of each culm (bottom, middle and top) were selected. At least seven samples of each section were extracted and tested (so the samples taken from the same piece of bamboo have similar characteristics). The natural moisture content of each sample was modified to determine the strength with different moisture content. The method to vary the moisture content used in the research guaranteed that each group of samples, with similar characteristics, had a moisture-controlled variation. Colombian Technical Standard NTC 5525 "Methods for testing the physical and mechanical properties of Guadua Angustifolia Kunth were followed to determine the tensile strength parallel to the fiber, as well as to determine the material moisture content. Tensile tests were performed after immersing the specimens in water for about 72 hours, when the material showed a pronounced variation in moisture content. Finding that tensile strength did not show an obvious decrease, the range of moisture content was reduced to less than 35%. In order to have all the information with samples with moisture content below of that percentage, the tests were carried out during a 3-hour range of time. Results showed that tensile strength of parallel fiber does not decrease as the moisture content of the material was increased in the moisture content range where the material is used as a structural element.

A Comparison of Geometry Effect on Tensile Testing of Wood Strands

Abstract There is currently no ASTM standard for testing the tensile mechanical properties of strands used in wood-strand–based composites. In this study we compared the ultimate tensile strength (UTS) parallel to grain and tensile modulus of elasticity (MOE) for southern pine (Pinus spp.) wood strands from an oriented strand board plant in which one treatment consisted of rectangle-shaped specimens and the other treatment consisted of samples milled into a tapered (“dog-bone”) shape. For bone-shaped samples, the measurements observed were 16 and 27 percent higher for MOE and UTS, respectively, than for the rectangular samples, and this was attributed to the generally accepted fact that dog-bone–shaped geometry yields measurements that are closer to true population parameters. Variation in mechanical properties was not statistically different for the two test methods. This study quantified that tensile testing of the rectangular strands will underestimate the true strength and MOE of the southern pine material. Because both methods resulted in similar levels of variability in test results, in-plant testing, using the traditional rectangular sample, may be acceptable for quality control as long as there is a recognition that the UTS and MOE values will be substantially more underestimated than those of smaller, dog-bone–shaped samples. As such, for future standards development, consideration should be given to the geometry of the strand when determining mechanical properties. Given the large amount of studies that use rectangular strands, there may be a need for a methodology to relate test results for rectangular and bone-shaped specimens.

Einfluss einer hydrothermischen Behandlung auf die Scherfestigkeit einer Buchenholzverklebung

The Influence of hydrothermal treatment on bond shear strength of beech (Fagus orientalis) wood specimens was studied. Wood samples were treated in a reactor at temperatures of 130 and 150 ∘C for a holding time of 30 minutes. For determining the bond shear strength in treated woods, wood blocks were bonded with urea formaldehyde, polyvinyl acetate and epoxy. Shear strength parallel to the grain of wood samples was also measured. Density, shrinkage, pH, contact angle and water absorption of the treated and untreated wood blocks were determined. Results showed a reduction in bond shear strength and shear strength parallel to grain due to hydrothermal treatment. The density, shrinkage and the contact angle of treated wood blocks increased; however the water absorption and the pH were reduced by applying temperature treatment.

Wood Properties of Young Acacia mangium Trees Planted in Indonesia

Abstract This study evaluated the wood properties of 5- and 7-year-old Acacia mangium trees planted in West Java, Indonesia. A plot (20 by 20 m) was selected in each stand. The stem diameter and stress-wave velocity (SWV) were measured for all trees (n = 24 and 18 for 5- and 7-y-old trees, respectively) in the plots. Core samples were taken from all trees in each plot using an increment borer to measure the basic density (BD) and compressive strength parallel to the grain (CS). The mean ± standard deviation stem diameter was 13.1 ± 3.0 and 21.9 ± 3.8 cm in 5- and 7-year-old trees, respectively. There was no significant correlation between stem diameter and SWV. The mean BD and CS for 5-year-old trees were 0.42 ± 0.02 g cm−3 and 30.0 ± 4.4 MPa, respectively, and for 7-year-old trees were 0.45 ± 0.02 g cm−3 and 32.8 ± 3.6 MPa, respectively. There was a positive correlation between BD and CS in 5- and 7-year-old trees (r = 0.790 and 0.583, respectively). The radial variation patterns for BD and CS were similar in 5- and 7-year-old trees: BD and CS gradually increased to about 6 cm from the pith, after which it was almost constant toward the bark. The results suggest that xylem maturation depends on the growth diameter in A. mangium.

Mechanical properties of poplar wood (Populus alba) dried by three kiln drying schedules

The influence of three drying schedules on the selected mechanical properties of poplar wood (Populus alba L.) was evaluated in terms of suitability for structural applications. For this purpose, 70 mm-thick poplar lumber was conventionally dried by three different moisture content based schedules of T5-D2, T5-D4, and T5-D6. In these schedules, the wet bulb depression was changed as a means of increasing of the drying intensity. After drying, the mechanical properties of the lumber, including bending properties (MOE and MOR), toughness, shear strength parallel to grain, and tensile strength perpendicular to grain, were measured. Results revealed that the severe drying schedule (T5-D6) caused higher reductions in the mechanical properties of the dried boards, particularly the MOE and MOR. Furthermore, toughness and tensile strength perpendicular to grain were not affected by the increasing of the wet bulb depression. The influence of all the three adopted schedules on the mechanical properties was evaluated using the drying rate, final moisture content gradient, and qualitative characteristics of the dried boards.

PHYSICAL AND CHEMICAL PERFORMANCE OF EUCALYPTUS WOOD WITH IMPREGNATED CHEMICALS

Methylolurea and carbamide were used to impregnate eucalyptus wood to improve its physical and chemical properties. The physical properties and dimensional stability were examined. TGA was used to evaluate the thermal stability of the wood. FTIR was used to state the changes of functional groups. The changes of wood structure were observed by SEM. The results showed the bending strength and compressive strength parallel to the grain increased by 15.10% and 16.78%, respectively. The basic density of modified wood was improved by 14.29%. The shrinkage of volume and swelling of volume were significantly decreased compared to the untreated wood. The TGA results indicated that the mass loss was around 8% during the second stage, from 120°C up to 280°C, while the mass loss of treated wood was around 4%. The treated wood exhibited LOI (limited oxygen index) values of about 42%, while the natural wood exhibited a LOI value of 22%. The FTIR analysis successfully showed that chemical bond was produced between wood and methylolurea as a result of chemical reaction between wood and methylolurea. The SEM results indicated that the transverse and tangential sections of the treated specimens were filled with the reaction products, which can prevent the absorption of moisture.

Physical and chemical performance of eucalyptus wood with impregnated chemicals

Methylolurea and carbamide were used to impregnate eucalyptus wood to improve its physical and chemical properties. The physical properties and dimensional stability were examined. TGA was used to evaluate the thermal stability of the wood. FTIR was used to state the changes of functional groups. The changes of wood structure were observed by SEM. The results showed the bending strength and compressive strength parallel to the grain by 15.10% and 16.78%, respectively. The basic density of modified wood was improved by 14.29%. The shrinkage of volume and swelling of volume were significantly decreased to the untreated wood. The TGA results indicated that the mass loss was around 8% during the second stage, from 120°C up to 280°C, while the mass loss of treated wood was around 4%. The treated wood exhibited LOI (limited oxygen index) values of about 42%, while the natural wood exhibited a LOI value of 22%. he FTIR analysis successfully showed that chemical bond was produced between wood and methylolurea as a result of chemical reaction between wood and methylolurea. The SEM results indicated that the transverse and tangential sections of the treated specimens were filled with the reaction products, which can prevent the absorption of moisture.

Cell Morphology and wood properties of Shorea Acuminatissima Planted in Indonesia

In view of the importance of long-rotation plantation forestry in SE Asia to limit soil erosion, the cell morphology and wood properties of 35-yearold plantation trees of yellow meranti, Shorea acuminatissima Sym. were studied. To understand the effects of growth rate on cell morphology and wood properties, 131 trees in a stand were classified according to their stem diameter as fast-, medium-, and slow-growing. Five trees in each category were selected for determining the cell morphology and wood properties. There were significant differences in vessel diameter, vessel frequency, and cell wall thickness of wood fibers in the three categories. The fast-growing trees had a relatively low frequency of wide vessels and thick-walled wood fibers. However, no significant differences in basic density or compressive strength parallel to grain were identified in the three categories. The radial variation in the cell morphology and wood properties showed an almost identical pattern in the three categories, suggesting that xylem maturation depends on the cambial age rather than growth rate.