An alternative solution for the determination of elastic parameters in free–free flexural vibration of a Timoshenko beam

An alternative inversion solution is presented to compute the elastic parameters based on the Timoshenko equation of motion in free flexural vibration. The interest of this solution was its relatively simple formulation and its validity domain, which was not restricted to the initial frequencies and a certain range of length-to-height ratio. The uniqueness of the solution was verified numerically, and the best optimization strategy was deduced. It was underlined that the shear modulus determination depended on the length-to-height ratio coupled with the number of resonance frequencies involved in the computation. The accuracy of the computed elastic modulus values was in the same scale as that for the measurement errors of frequency. However, the sensitivity of the shear modulus was found to be very high and depended on the number of frequencies taken into account. The theoretical model was found to be more accurate and to better estimate the frequency values than a classic solution of the Timoshenko equation. Furthermore, the inversion procedure gave equivalent elastic property values to those obtained with a classic solution (in the validity range of the classic solution) and was more robust when the number of frequencies taken into account was low.     

Effective lateral resistance of timber–plywood–timber joints connected with nails

In this study, an experimental study was conducted on the nailed timber–plywood–timber joints extended from the standard wall–floor joints of wooden light frame constructions, where the bottom plates of shear walls are nailed to the floors consisting of joists and floor sheathings nailed to them. The principal conclusions are as follows: The allowable lateral resistance of the nailed timber–plywood–timber joints can roundly be estimated by neglecting the plywood panels if their densities are higher than those of the timber main-members and they are fastened effectively onto the timber main-members. The stiffness of the timber–plywood–timber joints is less than that of the control timber–timber joints, which is improved by increasing the number of nails used to fasten the plywood panels onto the timber main-members. The stiffness of the joints whose floor sheathings are glued onto the joists is equivalent to the control timber–timber joints. The timber–plywood–timber joints with appropriate specifications have greater energy capacity until the failure than that of the control timber–timber joints. This ensures their energy capacity, which is important in dynamic resistance, to be equivalent to the control timber–timber joints.     

Practical techniques for the vibration method with additional mass: effect of crossers’ position in longitudinal vibration

The effect of the crosser’s position used for piled lumber on longitudinal vibration was investigated. As a model case, specimens with and without a concentrated mass were compressed in their thickness direction at nodal and antinodal positions of longitudinal vibration, following which, longitudinal vibration tests were conducted. Density and Young’s modulus were unaffected by compression of the specimen at the nodal position but was affected by compression at the antinodal position. By placing crossers at the nodal positions, accurate density and Young’s modulus values can be determined using the vibration method with additional mass without the influence of weight of the upper lumber.     

Physiological testing of blood for great bustard

lntroductionGreatbustard(otist8rd8)islistedasafirst-ratingpFoteCtedanimalinChina,mainIydistributinginthegrasslandarea.Thebirdpreferseatingtendergrass,seed,insect,fishandshrimp,etc.,fondofflying,andhasgre8terbodysize.GreatbustardhavetraitofsexualconceaIment,beingeasiIyagitated,unlikeIytamed.Withtheconstantaggravationofthehumaninterference,itspopuIationquantityisconstantIydecreasing.Therefore,itisverysignificanttocarryoutthefurtherstudyonthebiFd.ManyresearcheshavebeendoneonthisbirdinecoIogy…     

Analysis of moisture diffusivity of larch timber during convective drying condition by using Crank＇s method and Dincer＇s method

Two analytical procedures （Crank＇s method and Dincer＇s method） for porous solid materials were reevaluated and used to determine moisture diffusion coefficients and moisture transfer coefficients for larch lumber subjected to drying. A diffusion-like equation was used to describe drying process data. The lumber was idealized in the modeling as infinite plates. The moisture transport process inside the board was assumed to be one-dimensional. The macroscopic drying kinetics curves of larch timber at particular conditions were determined experimentally. Based on these data, calculation for both the moisture diffusion coefficients and moisture transfer coefficients by the Dincer＇s analytical procedure were made. The dynamic moisture diffusion coefficients by the traditional Crank＇s method were calculated. In general, diffusion coefficients calculated by the Dincer＇s method were all higher than those by Crank＇s method. These results could be due to the differences between two analytical methods and also different characteristics between solid moisture diffusion process and heat transfer process. Therefore the analysis and solution procedures of moisture diffusion differential equations need to be adapted in the future. With drying temperature＇s increasing moisture diffusion coefficient （D） and moisture transfer coefficient （k） increases accordingly. Also the relationships between diffusion coefficients and temperature as well as material moisture contents were analyzed by using Arrhenius equation and bound water transport theory.     

Dynamic responsive characteristics of nailed plywood–timber joints under harmonic vibrations

Dynamic tests of nailed plywood–timber joints are conducted under harmonic vibrations from 2 to 7 Hz. The principal results are as follows: under dynamic loading, nailed plywood–timber joints may break in low-cyclic bending fatigue failure of nails besides the other failure modes typical under static loading. The dynamic response of nailed plywood–timber joints is clearly dependent upon both the input frequency and the acceleration. These responsive characteristics arise from the nonlinear load–slip relationships and the characteristic cyclic stiffness degradation of nailed joints; that is, the cyclic degradation of the equivalent linear stiffness decreases the resonant frequencies of the same joints, which results in a transition of dynamic responses. It indicates that frequency components of seismic waves resonant to the frequencies corresponding to safety-limit stiffness of nailed joints may lead them to critical failures, even if the accelerations do not exceed the accelerations equivalent to the static damage-limit resistance.     

Laboratory and environmental decay of wood–plastic composite boards: flexural properties

The flexural properties of wood–plastic composite (WPC) deck boards exposed to 9.5 years of environmental decay in Hilo, Hawaii, were compared to samples exposed to moisture and decay fungi for 12 weeks in the laboratory, to establish a correlation between sample flexural properties and calculated void volume. Specimens were tested for flexural strength and modulus, both wet and dry, at 23°C and 52°C. Some specimens degenerated to only 15% of original flexural strength. UV radiation had no impact on flexural properties of field-exposed boards; loss occurred mainly on the side opposite to the sun-exposed surface. The mechanism of the aging process on colonization of WPC by fungi was examined and is consistent with development of slow crack growth in the polyethylene matrix combined with wood decay by fungi. Wood particle decay, moisture, and elevated temperature were the major factors causing composite degradation, indicated by accumulation of voids and a severe decrease in flexural properties. To simulate long-term field impact (including decay) on WPC flexural properties in the laboratory, conditioning of specimens in hot water for an extended period of time is required. Exposure to water (70°C/5 days) was adequate for simulating long-term composite exposure in Hawaii of 4?×?15?×?86 mm³ specimens.     

Effect testing of the chemicals for controlling pine needle bright

AIargeareaofscotchpines(PinusSyvesthevar-mongoHCa)wasdestroyedbySoptOrfapIhFPutffil8eandDothisbomapiniinHonghuaerjiforestregion,lnnerMongolia,in199o~1997.TheoutputSofseedsandconeswerereduced.NorepoFtoncontroIofSePtOFiapinFPutffiI8ehasbeenfoundinChina.ThetwodiseasesmostseriouslydestroyedscotChpines.ln199o~1994,theinfeCtedrateofnurserystockreached97.3%andabout6oooohm2treeswereinfeCtedindifferentdegrees.Atpresent,thecontroItechniqueforthemixedinfeCtionofthetWodiseaseshasnotbeenreporte…     

Nonlinear fixed and random generalized height–diameter models for Portuguese cork oak stands

• Objective   

The objective of the research was to develop a generalized height–diameter model for Quercus suber L. in Portugal, which can be applied both to undebarked and debarked trees, with diameter at breast height over cork larger than 2.5 cm.     

Cost sharing for timber stand improvements: Inducement or crowding out of private investment?

Cost sharing has been widely used to encourage the management of privately owned forests. While there is evidence of its capacity to promote management activities, it still remains open whether cost sharing induces additional private investments or whether it substitutes public funds for private capital. This study re-examines the latter issue in the case of Finnish family forest owners' pre-commercial and restoration thinnings using data from a nation-wide survey (n = 3801). A two-step model of cost-share participation and stand improvements is used to account for the endogeneity of cost-share participation. Cost-share participation was related to personal assistance and clearly encouraged forest owners' engagement in and extent of stand improvements. The inducement or crowding out of private capital is analytically shown to depend on the relative magnitude of forest owners' response to cost-share incentives in each specific situation. In the present case evidence suggests that cost sharing has had an inducement effect on private investment. This is likely related to the advanced personal assistance that has promoted the knowledge of and participation in cost sharing. The findings suggest that cost sharing can be a useful component in a balanced policy mix especially when combined with informational instruments.     

Determining Young’s modulus of timber on the basis of a strength database and stress wave propagation velocity I: an estimation method for Young’s modulus employing Monte Carlo simulation

In this article, we report on an estimation method for Young’s modulus that entails measuring only the stress wave propagation velocity of timber built into structures such as wooden buildings. Methods of estimating Young’s modulus that use the stress wave propagation velocity and characteristic frequency of timber in conjunction with timber density have long been used. In this article, we propose a method of easily and accurately estimating Young’s modulus from the stress wave propagation velocity without knowing the timber density. This method is based on a database of wood strength performance and density accumulated from a variety of research data and the method estimates Young’s modulus by a simulation method. We compared the Young’s moduli estimated by this method with those obtained by the bending test and by the measurement of the stress wave propagation velocity and density, and found similar results. This coincidence suggests that the method of estimating Young’s modulus presented in this article is valid. For example, the method is effective for convenient evaluation on site when determining whether a wooden building’s structural components should be reused or replaced when repairing or remodeling a building.     

A novel NIRS modelling method with OPLS-SPA and MIX-PLS for timber evaluationOA

The identification of timber properties is important for safe application. Near Infrared Spectroscopy(NIRS)technology is widely-used because of its simplicity, efficiency, and positive environmental attributes. However, in its application, weak signals are extracted from complex,overlapping and changing information. This study focused on the stability of NIR modeling. The Orthogonal Partial Least Squares(OPLS) and Successive Projections Algorithm(SPA) eliminates noise and extracts effective spec...     

A method for visualizing cesium ions adsorbed on wood charcoal using SEM–EDX

A new method based on scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDX) was developed for visualizing the distribution of cesium ions (Cs⁺) adsorbed by Japanese cedar charcoal. After being soaked in saturated aqueous CsCl solutions, wood charcoal and regular wood samples were embedded in resin, and thin sections of sample were prepared for the Cs⁺ observations. The Cs⁺ ions on charcoal could be seen in EDX mapping images and also in line profiles with enough contrast to identify differences between the various carbonized cell wall regions. On the other hand, Cs⁺ could not be observed in the EDX mapping images of wood samples, despite having been soaked in a saturated aqueous CsCl solution. These results indicate that Cs⁺ adsorbed on charcoal can be visualized using this method, but not Cs⁺ in wood. Additionally, oxygen detected on the charcoal by EDX can be regarded as an indicator of the presence of surface functional groups.     

Structural development of Pinus sylvestrís stands with varying initial density: A preliminary model for quality of sawn timber as affected by silvicultural measures

The effects of stand density, thinning and pruning on the quality of sawn timber of Scots pine (Pinus sylvestris L.) were studied based on a computer model. Procedures for the tree growth and crown structure produce a tree, whose properties in terms of location, dimensions and quality (living, dead) of branches are known for any moment of the selected rotation. Consequently, the size, quality (living, dead) and location of knots in sawn timber are recognizable allowing the grading of sawn pieces. The model computations showed that the natural dynamics of the crown system in narrowly‐spaced stands could yield sawn timber nearly of the same quality as resulted from pruning in widely‐spaced stands. Thinning increased the branch growth and the branchiness of the wood yielding lower grade for sawn pieces, respectively.     

Validity limits of Kubelka–Munk theory for DRIFT spectra of photodegraded solid wood

The validity of the Kubelka–Munk (K-M) theory was investigated to determine the IR absorption spectra of wood based on diffuse reflection infrared Fourier transform (DRIFT) measurements taken on photodegraded samples. After analysing plenty of DRIFT spectra of wood and examining the shape of the K-M equation, it can be concluded that the measured K-M function can be used as an absorption spectrum if the values of the function are below 14 K-M units. Above this limit, the K-M theory, which was created for poorly absorbing materials, does not give the absorption of wood properly. If a matt aluminium plate is used as a background material and the values are between 14 and 40, absorption changes can be calculated after normalisation of the spectra. This normalising manipulation is only successful if there is an absorption peak close to the examined one which does not change its absorption during the photodegradation.     

Phenol–formaldehyde impregnation of densified wood for improved dimensional stability

To produce a highly stable wood-based product with increased mechanical properties, phenol formaldehyde (PF) resin impregnation was combined with the viscoelastic thermal compression (VTC) process. Dimensional stability and bending stiffness were evaluated. Two PF resins with weight average molecular weights of 172 and 780 were studied at three different concentrations, 5, 10 and 20%. After 24-h room temperature water soak and 2-h boil, both PF treatments at all concentration levels showed high levels of dimensional stability compared to non-impregnated VTC processed controls. The higher molecular weight PF provided greater stability with an average thickness swell value of 12% compared to 20 and 37% for the lower molecular weight PF resin treatment and control, respectively. High anti-swelling efficiency values were recorded for both low and high molecular weight resins, implying these modifications were effective at reducing the volumetric swelling which occurred in the unmodified control. PF treatments were also extremely effective at reducing irreversible swelling. The low and high molecular weight resin treatments had 1/5th and 1/7th the irreversible swelling than the unmodified VTC processed controls, respectively. All dimensional stability values improved as resin concentrations increased. Both resin types at all concentration levels reduced Young’s modulus.     

Characterization of different wood samples using a new combined method of evolved gas analysis and pyrolysis–gas chromatography/mass spectrometry

Evolved gas analysis (EGA) in combination with analytical pyrolysis is presented as a new technique for rapid investigations into wooden materials. In a first analytical step, the thermal behaviour of three wood samples was determined by EGA. Based on these results, analytical pyrolysis–gas chromatography/mass spectrometry was carried out to investigate the influence of wood-specific thermal behaviour and the chemical composition on the results. Furthermore, the influence of sample mass and particle size was examined.     

The potential of SilviScan’s X-ray diffractometry method for the rapid assessment of spiral grain in softwood, evaluated by goniometric measurements

The orientation of the tracheid cells with respect to the stem axis (grain angle, spiral grain) exerts a strong influence on numerous material properties. Therefore, several methods have been developed to assess this wood anatomical feature. The current study compares SilviScan spiral grain measurements, which uses X-ray diffractometry, with direct goniometer readings. The correlation between these two methods yielded an r² of 0.874 and a root mean square error of prediction (RMSEP) of 1.21 clearly demonstrating that X-ray diffractometry can provide accurate and rapid information on the grain orientation in Norway spruce (Picea abies (L.) Karst.) or similar structured softwoods.