Clear Specimens Research Articles

Comparative Study on Clear Specimen Strength and Member Strength of Side‐Pressure Laminated Bamboo

Side‐pressure laminated bamboo (LB) made from heat‐modified, fast‐growing bamboo is introduced in this document. As a relatively new type of bamboo composite fabricated by bamboo strips, side‐pressure LB has some favorable mechanical properties, such as thermal insulation, light mass, high strength, and earthquake resistance. To promote the application of side‐pressure LB in structural engineering, according to the test standards for timber, the mechanical properties of bamboo, including tensile strength parallel to the grain, compressive strength parallel to the grain, bending strength and bending modulus, and shear strength parallel to the grain, were obtained by testing clear bamboo. Meanwhile, the bending and shear tests were performed on full‐sized beams of side‐pressure LB. Comparing the strength of clear bamboo and full‐sized bamboo beams under bending and shear, explore the effect of size on bending and shear strength. The results demonstrate that the size effect has a significant influence on the bending strength, and the bending strength decreases clearly with the increase of the span of member; the shear strength is mainly affected by the shear area and decreases with the increase of the shear area. Based on the measured indicators of shear strength, a formula suitable for converting the shear strength of clear bamboo to full‐sized bamboo beam is proposed. And the recommended design strengths of bamboo are given by using the limit state method, which provides a design basis for the engineering application of bamboo.

Developmental features of the canid proximocaudal femur.

We continued direct morphological studies of the canid coxofemoral joint, considering early-life spatial relationships around the locus of the proximocaudal joint capsule insertion. Our primary goal was to elucidate the postnatal developmental gross anatomy of the proximocaudal femur, among juveniles across Canidae. From an original database of 267 independent (museum) specimens from 11 canid taxa and 1 hybrid taxon, we identified 29 ancient or modern candidate juvenile specimens (nine taxa and one hybrid taxon). Based on optimal ability to recognize landmarks, the best photographic data were categorized into five groups of four each (n= 20). The data groups approximated early juvenile, early-mid juvenile, mid-juvenile, mid-late juvenile; and young adult stages. In this descriptive photographic essay, we demonstrate the developmental spatial proximity among (a) the dorsal meeting of the respective lateral and medial extensions from the growth centers of the femoral head and greater trochanter; (b) the caudodorsal aspect of the coxofemoral joint capsule attachment; (c) a segment of the proximocaudal femoral shaft physis; and (d) an eventual associated mineralized prominence. The latter occurs frequently but not universally, suggesting natural population variability across taxa. Across taxa and juvenile age categories, the morphology thus supports developmental conservation among ancient and modern Canidae. The biomechanical and biological cause-effect implications are not yet clear. For zoological purposes, we apply the term postdevelopmental mineralized prominence to the residual caudolateral surface feature. We extend the original anatomical work of Morgan in zoological and phylogenic arenas, using direct observation of cleared skeletal specimens.

Long-term bending properties of cross-laminated timber made from Japanese larch under constant environment

Cross-laminated timber (CLT) has been used extensively in timber construction. CLT panels are typically used in roofs and floors that carry a continuous load, and it is important to examine the long-term loading capacity of CLT. However, studies that focus on the long-term loading capacity of CLT are limited. To this end, we conducted long-term out-of-plane bending tests on seven-layer CLT made from Japanese larch (Larix kaempferi) under constant environmental conditions, investigated creep performance and duration of load, and experimentally analyzed creep rupture behavior. The mean estimated relative creep after 50 years was 1.49. The sample showed a satisfactory resistance to creep as a building material. The duration of load of most of the specimens in this study was shorter than the conventional value of small clear wood specimens. Specimens had a lower duration of load capacity than solid lumber. According to the results of survival analysis, a loading level of 70% or more caused the initial failure of specimens. Creep rupture of most of the specimens occurred at less deflection than displacement at failure in the short-term loading test. Additional studies focusing on the effects of finger joints, transverse layers, and width of a specimen on creep rupture behavior are suggested.

Characterisation and grading of four selected timber species grown in Nigeria in accordance with Bs 5268


 
 
 This study presents a development of strength classes for Vitex doniana, Diospyros mespliformis, Parkia biglobosa and Isoberlinia doka, northern Nigeria timber species in accordance with BS 5268-2 (2002) and NCP 2 (1973). The specimens for the experimental measurements were obtained from timber-sheds in Zaria, Kaduna - Northern part of Nigeria. The laboratory experiments were conducted to determine the physical and mechanical properties of the selected timber species. The specimens were prepared in accordance with BS 373 for small clear specimens for the determination of physical and mechanical properties. Flexural strength properties were determined using three point bending test. Adjustment was made on the mechanical properties at moisture content of 12% and 18% in conformity with BS 5268-2 (2002) and NCP2 (1973) respectively. The laboratory data were analyzed using data analysis tool pack in Microsoft excel 2019 to generate the mean, coefficients of variation and theoretical distribution models which form the uncertainty models. Basic and grade stresses were also computed using experimental failure stresses. The selected timber species were then classified using the grade bending stress, density and mean modulus of elasticity obtained. Vitex doniana, Diospyros mespliformis, Parkia biglobosa and Isoberlinia doka were assigned to strength classes D30, D40, C40 and D30 in accordance with BS 5268-2 (2002) respectively. Similarly, in accordance with the NCP 2 (1973), these species belong to N4, N3, N4 and N3 respectively. The results obtained show that Vitex doniana, Diospyros mespliformis and Isoberlinia doka are hardwoods whereas, only Parkia biglobosa is a softwood species.
 
 

Mechanical properties of secondary quality beech (Fagus sylvatica L.) and oak (Quercus petraea (Matt.) Liebl.) obtained from thinning, and their relationship to structural parameters

• Key message This paper investigates the juvenility limit and structure–property relationship in secondary quality beech ( Fagus sylvatica L.) and oak ( Quercus petraea (Matt.) Liebl.). The juvenile wood occupies a very small area near the pith. The stabilization of the different parameters varies over time. Adding the microfibril angle (MFA) and the grain angle to the MOE prediction model significantly improves the quality of the model, despite little variation in both parameters. • Context Using secondary qualities and small logs of hardwoods such as beech and oak for engineered wood products is an increasingly important issue due to the technological challenges of processing smaller logs and denser woods. Secondary quality hardwoods are expected to have less variation in mechanical properties compared to softwoods with high juvenile wood content. • Aims The first objective of this study was to investigate the radial variation in wood properties of suppressed growth beech and oak trees obtained from thinning operations. The second objective was to develop a model to predict the mechanical properties of these hardwood species based on their structural parameters. • Methods The microfibril angle, ring wood density, and ring width from the pith to the bark were determined using an X-ray densitometer. The modulus of elasticity and modulus of rupture were evaluated on the small clear specimen using a three-point bending test. The wood density, grain angle, and microfibril angle of this small clear specimen were also measured. • Results The results show that the juvenile wood in oak has a wider ring and higher microfibril angle, whereas it has wider latewood and higher microfibril angle in beech. For both species, the juvenile wood occupies a very small area, less than 5 cm from the pith. The mechanical properties of oak and beech wood from suppressed growth trees are comparable to properties reported in the literature for dominant trees. The modulus of elasticity of oak was best predicted using wood density, grain angle, and microfibril angle. The modulus of rupture of oak is better predicted with wood density and grain angle, whereas it is best predicted with wood density alone for beech. • Conclusion Juvenile wood found in the suppressed growth trees of both hardwoods can be used in place of mature wood. It is important to take structural parameters into account when predicting the mechanical properties of hardwood species.

Assessing the density and mechanical properties of ancient timber members based on the active infrared thermography

The objective of this study was to assess the density and mechanical properties of ancient timber members based on the active infrared thermography (IRT). Based on the unsteady heat transfer theory, the cooling constant (Ve) was proposed and the relationship between Ve and density as well as the mechanical properties of timber was analyzed. The cooling tests were conducted on 50 small clear specimens of ancient timber members to obtain the Ve and the cooling law of specimens. In addition, the effect of heating on the dynamic modulus of elasticity (Eus) and color of ancient timber members was investigated. At the same time, static mechanical tests and density measurement test were carried out to analyze the relationship between Ve and density as well as mechanical properties. The results indicated that there was unobservable influence on Eus and color parameters (L*, a* and b*) of specimens with its heating process in evaluation of the density and mechanical properties based on active IRT. Meanwhile, the initial excess temperature θ0 and initial temperature T0 had no influence on the cooling constant Ve as well as the relationship between τ and θ in the cooling process of specimens. Moreover, Ve had a strong negative correlation with density, modulus of elasticity (MOE), modulus of rigidity (MOR) and compressive strength parallel to grain (CSPG) of specimens (R2 = 0.9768, 0.8493, 0.8714 and 0.8865). In addition, the validation test result show that there is satisfactory predictive ability for density, MOE, MOR and CSPG of ancient timber members based on the prediction models established.

An Investigation of the Duration of Load of Structural Timber and the Clear Wood

In this study, DOL of structural timber and the clear wood and DOL of modulus of elasticity of wood were investigated. The dimension lumber of Spruce-Pine-Fir of Grade No. 2 and Grade No. 3 and the small clear specimens of the same species of the dimension lumber were used to conduct the short-term and the long-term bending test. The short-term strength distributions of the dimension lumber and the small clear specimens were obtained. The long-term tests were conducted under constant environmental conditions for 18 months. The sample matching technique was used to estimate the short-term strength of the specimens that underwent long-term tests. It was found out that there is virtually no difference in DOL between different grades or quality of lumber and no difference between structural timber and clear wood, and DOL obtained from the test of this study is more in agreement with Wood’s curve. A threshold stress ratio of about 0.55, loaded above which the wood began to experience strength loss, was revealed from the test. Making use of the threshold ratio concept, the DOL of wood can be obtained not only from failed specimens under load in the process of the long-term loading, but also from the ramp loading test of the specimens that survived the long-term test. Sustained load also poses DOL on the modulus of elasticity of wood, though to less degree than DOL of strength of wood.

Variation in Wood Properties of Hybrid Poplar Lumber by Radial and Vertical Position in Stem: A Case Study from Boardman, Oregon

Understanding of wood quality of hybrid poplar is critically important for manufacturers who want to know the suitability of the wood for specific products. To this end, lumber was milled from the merchantable stem of four hybrid poplar clones ages 10-11 yr., grown at single site near Boardman, OR. The vertical and radial position in the stem were recorded for each board and the boards were kiln dried, surfaced, and samples from each board tested to determine specific gravity (SG), dimensional stability, hardness, screw withdrawal, and bending strength and stiffness (modulus of rupture [MOR] and modulus of elasticity [MOE], respectively) from small clear specimens. Results show differences in wood properties relative to vertical and radial position in the stem. SG, hardness, screw withdrawal, and bending properties of lumber samples generally increased with height in tree. Tangential hardness, SG, and MOR varied significantly between different sides of the trees corresponding to predominant wind in the area. Boards milled from the center of the stem had lower MOE and MOR than boards milled from nearer the bark. The results of this study may be used to target specific stem locations for different end uses.

A three-dimensional numerical analysis of moisture flow in wood and of the wood\u2019s hygro-mechanical and visco-elastic behaviour

A three-dimensional numerical model was employed in simulating nonlinear transient moisture flow in wood and the wood’s hygro-mechanical and visco-elastic behaviour under such conditions. The model was developed using the finite element software Abaqus FEA®, while taking account of the fibre orientation of the wood. The purpose of the study was to assess the ability of the model to simulate the response of wood beams to bending and to the climate of northern Europe. Four-point bending tests of small and clear wood specimens exposed to a constant temperature and to systematic changes in relative humidity were conducted to calibrate the numerical model. A validation of the model was then performed on the basis of a four-point bending test of solid timber beams subjected to natural climatic conditions but sheltered from the direct effects of rain, wind and sunlight. The three-dimensional character of the model enabled a full analysis of the effects of changes in moisture content and in fibre orientation on stress developments in the wood. The results obtained showed a clear distinction between the effects of moisture on the stress developments caused by mechanical loads and the stress developments caused solely by changes in climate. The changes in moisture that occurred were found to have the strongest effect on the stress state that developed in areas in which the tangential direction of the material was aligned with the exchange surface of the beams. Such areas were found to be exposed to high-tension stress during drying and to stress reversal brought about by the uneven drying and shrinkage differences that developed between the outer surface and the inner sections of the beams.

Application of pyrolysis acid from date palm waste as wood preservative

Matched sets of clear specimens of poplar and pine wood were treated with 3, 5, and 8% (v/v) aqueous solutions of slow pyrolysis acid (PA) derived from date palm waste, to evaluate the effectiveness of PA in controlling mold growth on species of wood. Chemical compounds available in PA were identified by gas chromatography-mass spectrometry analysis. Treated and control specimens were contaminated with Aspergillus sp., then incubated in accordance to AWPA E24 (2017). Percentages of occupied surface by mold on each of control and treated specimen with respect to its total surface were evaluated by Image-J software. Comparisons of mean values of these determined ratios and physical examinations showed that, depending on species, the 5 and 8% water solutions of PA prohibited Aspergillus growth on tested woods. Experiments were also conducted on a matched set of small clear specimens of beech wood, impregnated by 3, 5, and 8% water solutions (v/v) of PA, using full-cell process and contaminated with decay fungus (Trametes versicolor), then incubated. Specifications of the EN 113 (1996) standard were followed. Weight loss was applied for comparing control and treated specimens. Average values of weight losses indicated that the 5% solution was effective, but 8% solution presented a better result.

Mechanical Properties and Strength Grading of Engineered Bamboo Composites in China

Engineered bamboo composite (EBC) is a new high-strength anisotropic structural material, which has standardized sections and less inherent variability than the natural material. For safety reasons in structural applications, the characteristic values of mechanical behaviors are needed to build the design values utilized in practical application. Recent research studies on EBC focused on the mechanical properties from a single source, with little research on the sampling of the manufacturers. The present work investigates mechanical properties of two types of commercially available EBC—parallel strand bamboo (PSB) and laminated veneer bamboo (LVB). The main aim of this work is to evaluate the best probability distribution model (normal, lognormal, and Weibull) and mechanical properties for EBC in China and determine the characteristic values indicated by ASTM D2915. The mechanical properties in tensile, compression, and shear were evaluated using about 4300 small clear specimens from seven manufacturers in five raw bamboo origins of China. Based on the confidence band method, the strength grading of EBC subjected to compressive strength was developed with two predictors (density and MOE). By using intervals of each predictor, several strength grades were built. Each grade has the mean compressive strength, 5th percentile lower value (R0.05), and characteristic value (Rk), which could be used in structural design. This research contributes to the establishment of EBC standards and is essential for further accepting these materials in structural engineering.

Estimating Mechanical Properties of Wood in Existing Structures-Selected Aspects.

The paper presents and discusses selected methods of wood classification and the evaluation of its mechanical properties. Attention was mainly paid to methods that may be particularly useful for examining existing elements and structures. The possibility of estimating the modulus of rupture—MOR and modulus of elasticity—MOE based on the non- destructive (NDT), semi-destructive (SDT), and destructive tests (DT) were considered. Known international, European, and American standards and research approaches were indicated. The selected testing methods and their interpretation were presented. These were, among others, the method of visual assessment, the resistance drilling method, methods of determining the dynamic modulus of elasticity, and procedures for testing small clear specimens. Moreover, some of our own research results from the conducted experimental tests were presented and discussed. In the destructive tests, both large elements and small clear specimens were examined. The results obtained from individual methods were compared and some conclusions were presented. The summary discusses the fundamental difficulties and limitations in applying the presented procedures and interpretations.

Variability of the mechanical strength of Congo Basin timbers

ABSTRACT Wood has a very high variability compared to other construction materials. Such variability may be more important in the Congo Basin forest, in which hundreds of species are regularly exploited for trading in international markets. Reducing such a variability in construction applications is a major challenge since the characteristic values of strength properties may have penalizing effects on wood. The main objective of this work was to specify the mechanical strength variability of tropical timber species from the Congo Basin. Eighty-nine timber species were considered. Their mechanical properties were derived from small and clear specimen. The first step of the study consisted in identifying the mechanical groups in which the timber species may be assigned, by using the principle of variance’s decomposition. In the second step, the Monte-Carlo simulations were used in order to quantify the variability of the strength properties for each species. We found that the strength of the timbers can be organized in six distinct groups. The variability analysis revealed with a more precise information, the potential of the timber species to be assigned simultaneously to several strength categories. Potential applications may concern reliable and interchangeable uses of tropical timber species and a more efficient processing and grading.

Interrelationships of specific gravity, stiffness, and strength of yellow pine across five decades

The interrelationships among specific gravity (SG), modulus of elasticity (MOE), and strength (modulus of rupture, MOR) are largely the foundational basis for non-destructive evaluation and testing. Resource monitoring and commercial structural lumber production often rely upon such non-destructive evaluation to predict the bending and/or tension strength of individual members. These technologies require routine calibration. In addition, it is important to know the extent to which a given resource may change over time. To that end, this study investigated the relationship among SG, MOE, and MOR of small clear specimens from three samples taken across an approximate 50-year period; 1965 to 2018. Coefficients of determination among these variables are presented along with the prediction equations. These findings can be used to gain insight into the reliability and stability of these relationships over time.

A Review of Shear Properties for Malaysian Tropical Timber in Structural Size

In recent years, the studies on producing data on physical and mechanical properties of Malaysian timber specimens have evolved from small clear specimen to structural size specimen, where most of the research method was based on the American Standard Testing Manual ASTM D198. Numerous data regarding mechanical properties on structural size specimen have been produced through this method, such as bending and compression test. Unfortunately, studies on shear properties on structural size timber are very scarce. It has reviewed that the global timber researchers are focusing to produce data on shear properties of European timber species such as Oak, Spruce and Pine where both shear strength and shear modulus data were obtained from bending and torsion test. Furthermore, from the review of the existing literature, it is clear that there is no proper studies focusing on development of shear properties of Malaysian tropical timber, especially torsion test in accordance with EN 408:2010. Therefore, the aim of this study is to investigate the shear properties (shear strength and shear modulus) of Malaysian Tropical Timber in large size.

COMPRESSION AND TENSION CREEP BEHAVIOUR OF LVL SENGON (PARASERIANTHES FALCATARIA)

This study was aimed to investigate the creep behavior of laminated veneer lumber (LVL) Sengon,especially under the application of compression and tension stress parallel-to-the-grain. In IndonesiaLVL made from the fast-growing Sengon (Paraserianthes falcataria) species is designed to be usedas a substitution for solid wood in building construction. Creep test was conducted on the specimenswith reference to the ASTM D143‐09 standard test methods for small clear specimens of timber.Moreover, the constant loads were made equal to about 20%, 30%, and 40% of the 60% ultimateload derived from the static test and the creep test was conducted in a chamber having an averagetemperature of 25oC and minimum relative humidity of 65%. The results of creep test for a period of90 days showed that the creep factors were 0.51, 0.52, and 0.41, respectively for the specimens undertension stress level of 20%, 30%, and 40%, respectively. In the case of specimen under compressionstress parallel-to-the-grain, the creep factors were 0.42, 0.41, and 0.31, respectively, for stress levelequals to 20%, 30%, and 40%. It can be concluded that the creep factor under tension stress is slightlyhigher than that of specimens under compression stress, and these obtained creep factors are muchlesser than the values provided in the code.

Investigating the Underlying Effect of Thermal Modification on Shrinkage Behavior of Bamboo Culm by Experimental and Numerical Methods.

This study probes into the root cause of split in thermally modified bamboo culm by investigating the underlying effect of thermal contraction with respect to its orthotropic nature by experimental and numerical methods while concurrently monitoring the chemical variation of its structure by Fourier transformed infrared spectroscopy (FTIR). In first part of this study, a non-linear increase in dimensional and weight changes of small clear bamboo specimens were observed with increasing temperature. The dimensional changes in the radial and tangential directions significantly exceeded that in the longitudinal direction. From FTIR results, shrinkage effect between 150 °C to 200 °C was associated with weight loss engendered by reduction in weakly bound water and increase in desorption of water content while alteration of its mechanical properties was attributed to changes in cellulose, hemicellulose, and lignin. From results of finite element method (FEM), the graded variation in thermal expansion coefficient, which showed the formation of a narrowed region of strain concentration corresponding to longitudinal crack propagation, was associated with the inducement of internal forces, namely tensile and compressive forces, at specific regions along the culm length. The results of this study can be useful to achieve optimized durability in modified bamboo for construction.

Estimating mechanical properties of clear wood from ten‐year‐old Melia azedarach trees using the stress wave method

The objective of this study was to examine the potential of stress wave velocity (SWV) as a rapid and non-destructive method to estimate the mechanical properties of Melia azedarach wood. The SWV, dynamic modulus of elasticity (MOEd), modulus of elasticity (MOE), modulus of rupture (MOR, bending strength) and density were determined on ninety 20 ⋅ 20 ⋅ 320 mm clear wood specimens, obtained from stems of three ten-year-old M. azedarach trees, and tested at environmental equilibrium in 20°C, 60 % relative humidity (a moisture content of approximately 12 %). There was a statistically significant (0.1 % level) but weak correlation (R2 = 0.23) between the SWV and MOE, but no statistically significant correlation was found between the SWV and MOR. Much better results for prediction of static properties of M. azedarach wood were obtained when SWV and wood density (WD) were used together through calculation of MOEd in the air-dry condition (MOE: R2 = 0.76, MOR: R2 = 0.47), although in the case of MOR a model based on WD alone is slightly better (R2 = 0.58), and WD is also almost as good as MOEd for predicting MOE. It is concluded that SWV coupled with WD can be employed as a predicting parameter to evaluate the mechanical properties of M. azedarach wood during the manufacturing process, although WD alone is also effective. The SWV alone would not be useful due to MOE being almost directly proportional to WD at this moisture content.

Experimental investigation into the mechanical properties of scrimber composite for structural applications

Scrimber composite is a novel engineered wood-based construction material that is manufactured by reconstituting structural lumber using small-diameter tree species. In this study, clear specimens of the scrimber composite made from fast-growing poplar trees were tested to comprehend their mechanical properties; besides, a group of full-scale scrimber beams was tested to acquire the bending properties of structural-scale scrimber bending members. Then, comparison of mechanical properties was conducted among this scrimber composite, other common engineered wood, and bamboo scrimber. Finally, simplified longitudinal stress–strain models were proposed based on the experimental stress–strain relationships of the scrimber composite under the parallel-to-grain tension and parallel-to-grain compression scenarios. Results show that the scrimber composite can provide ideal mechanical properties, which are comparable or even superior to those of other common engineered wood/bamboo products. For the scrimber under the parallel-to-grain or perpendicular-to-grain compression, it is featured by ductile failure modes, such as crushing failure at the compressive zone and splitting failure with fractures propagating along the grain; whereas, for the scrimber composite under the shear, tension, and bending scenarios, it is featured by brittle failure modes, such as tension failure with flat fractures and shear failure along the bonding surface. Besides, it is proven that using the design strength of the clear specimens of the scrimber is reasonable and conservative for the design of structural-scale scrimber bending members. For the scrimber under the parallel-to-grain compression, the nonlinear characteristics of its stress–strain relationship can be described by one fourth-order polynomial function.

Yellow Pine Small Clear Flexural Properties across Five Decades

Abstract When discussing structural southern yellow pine lumber, questions frequently are asked regarding changes over time. This is a significant area of discussion given that structural lumber properties (i.e., design values) were changed around 2012. Climate change, forest management, genetics, processing, and others are listed among the many possible contributing factors. Of interest are these questions: (1) Are changes in bending properties permanent at some fundamental level, or are they somewhat dynamic and responsive to controllable factors? (2) To what degree have the basic southern pine wood mechanical properties changed over time? Related thereto, this research examines the bending properties of small clear pine specimens from three samples. Sample 1 was pulled from a production-weighted sample of in-grade parent lumber. Sample 2 was pulled from commercially available molding and millwork. Sample 3 was pulled from data from the U.S. Department of Agriculture Forestry Products Laboratory from the early to mid-1960s. The flexural properties of small clear specimens among the three samples showed some statistically significant differences. However, there was no clear trend regarding these differences. These results appear to support the notion that while the variability of pine's flexural properties is significant and that while many changes in forest management and production have occurred over the past five decades, the basic density and bending strength of clear southern pine appear generally stable over time.