Experimental verification and nonlinear modeling of truss-plate joints by Runge-Kutta numerical technique

The growing use of light-frame wood trusses in the residential and commercial construction has generated the need for general analysis procedures for predicting deformations and ultimate load of truss-plate joints, which are the basis for accurate evaluation of structural performance and design of complete truss assemblies. This dissertation was aimed at developing such a model. The developed model incorporates mechanisms of load transfer from one wood member through the truss plate and into another wood member and predicts the load-deflection trace and ultimate load. It treats plate teeth as beams on elastic foundation and applies Runge-Kutta numerical analysis to solve the governing differential equations. The nonlinear response of the foundation is accounted for by a linear step-by-step procedure. Additional theoretical investigation consisted of using an existing program to perform finite element analysis of plate joints to determine the interaction of plate teeth arranged in columns or in rows. This analysis showed some interaction among teeth in columns and none among teeth in rows. To develop data for model verification, tests were performed on joints made of Douglas-fir lumber and 20-gauge truss plates with die-punched teeth -for various grain and plate orientations. Foundation moduli of test joints were obtained by embedment testing under compression loads. Comparisons between theoretical and experimental load-deflection traces show acceptable agreement. Ultimate load was accurately predicted for specimens which failed as a result of tooth withdrawal, but not for either plate failure or wood failure perpendicular-to-grain, neither of which was included in the model. Possible future model improvements should consist of incorporating these two failure modes and a mechanism associated with moment transfer through plate joints

A Technique to Measure Strain Distributions in Single Wood Pulp Fibers

Environmental scanning electron microscopy (ESEM) and digital image correlation (DIC) were used to measure microstrain distributions on the surface of wood pulp fibers. A loading stage incorporating a fiber gripping system was designed and built by the authors. Fitted to the tensile substage of an ESEM or a Polymer Laboratories MINIMAT tester, it provided a reliable fiber straining mechanism. Black spruce latewood fibers (Picea mariana (Mill) B.S.P.) of a near-zero microfibril angle displayed a characteristically linear load elongation form. ESEM was able to provide real-time, high magnification images of straining fibers, crack growth, and complex single fiber failure mechanisms. Digital images of single fibers were also captured and used for subsequent DIC-based strain analysis. Surface displacement and strain maps revealed nonuniform strain distributions in seemingly defect-free fiber regions. Applied tensile displacements resulted in a strain band phenomenon. Peak strain (concentration) values within the bands ranged from 0.9% to 8.8%. It is hypothesized that this common pattern is due to a combination of factors including the action of microcompressive defects and straining of amorphous cell-wall polymeric components. Strain concentrations also corresponded well to locations of obvious strain risers such as visible cell-wall defects. Results suggest that the ESEM-based DIC system is a useful and accurate method to assess and, for the first time, measure fiber micro-mechanical properties

Changes in the Chemical Composition and Spectroscopy of Loblolly Pine Medium Density Fiberboard Furnish as a Function of age and Refining Pressure

Loblolly pine wood between the ages of 5-35 was refined into medium density fiberboard furnish at steam pressures from 2 to 18 bar. The effect of age and processing conditions on the properties of the fibers was assessed by wet chemical analyses, Near Infrared Spectroscopy (NIR) and powder X-ray diffraction (XRD). In general, the percentages of extractives and glucose increased, while the xylose, galactose, and mannose decreased with increasing refining pressure. There were no consistent changes in chemical composition of the refined fibers as a function of the age of the wood. The crystallinity of the refined fibers increased with both age and refining pressure. The spectroscopic and XRD data were analyzed using multivariate statistical methods, indicating a strong relationship between the spectral patterns and refining pressure

Nondestructive detection of proportional limit and prediction of destructive parameters

The conventional method for determining lumber strength depends on visual evaluation by lumber graders which often results in undergrading of lumber. Nondestructive proof testing is used less often and provides for only estimates of elastic moduli of elasticity and rupture. The evaluation of nondestructive variables such as proportional limit (PL) and acoustic emissions (AE), offers a possibility of not only improved predictions for elastic but also nonelastic moduli. A microcomputer-controlled testing machine was used to pretest three machine-stress-rated grades of Douglas-fir lumber up to PL under an accelerated deflection rate. These specimens were then tested to failure. The load, deflection, and AE were continuously monitored throughout the testing. The observations from nondestructive testing were chosen for independent variables in regression models for predicting the destructive parameters. It is found that PL can be determined in a microcomputer-controlled test, with the computer-detected PL highly correlated with PL determined from destructive testing (r = 0.92). Although this computer-detected PL, in combination with modulus of elasticity, is a good estimator of lumber strength (r = 0.83), it results in a poor prediction of ultimate deflection (r = 0.54). However, not only is a combination of AE variables below the PL and physical properties strongly correlated with PL Cr = 0.76), but the same combination is also strongly correlated to strength Cr = 0.93) and ultimate deflection Cr = 0.83)

The Application of Near Infrared (Nir) Spectroscopy to Inorganic Preservative-Treated Wood

There is a growing need to find a rapid, inexpensive, and reliable method to distinguish between treated and untreated waste wood. This paper evaluates the ability of near infrared (NIR) spectroscopy with multivariate analysis (MVA) to distinguish preservative types and retentions. It is demonstrated that principal component analysis (PCA) can differentiate lumber treated with CCA, ACZA, or ACQ preservatives. Furthermore, separation according to wood species and assay zone was also observed. Within the range of preservative concentrations available, partial least squares (PLS) regression was also performed on the NIR data, from which retention levels were predicted. The results highlight the potential for this technique to predict the concentration, as well as identify the type, of inorganic preservatives present

Finding a safe space: denning range dynamics of African wild dogs in Zimbabwe

African wild dogs utilise a den for ~10–12 weeks after birthing, during which home ranges are contracted and usually in areas away from roads and water sources, with low prey and predator abundances, high terrain ruggedness and vegetation cover. Our study in Savé Valley Conservancy (SVC) investigated which ecological and environmental factors determine the selection of denning areas and behaviours. Camera trap data collected from four den grids and three random den grids were analysed using binomial generalised linear and occupancy models. Denning wild dogs preferred areas with higher kudu and impala presence and areas closer to roads and water sources. Wild dogs may den in areas we perceive as riskier in an attempt to reduce energy expenditure when hunting. The detection of wild dogs strongly decreased with higher lion presence, while increasing with steeper slopes, higher vegetation cover and leopard presence. Given lion habitat preferences, SVC wild dogs could be using areas which reduce their exposure to lions, while solitary leopards do not necessarily pose a risk to wild dog packs. Our study highlights that the denning behaviours of wild dogs may be inconsistent both within and among populations, and that comprehensive research approaches be taken to understand their denning behaviours, assisting the development of appropriate management/conservation strategies

Ability of Near Infrared Spectroscopy to Monitor Air-Dry Density Distribution and Variation of Wood

Process control of wood density with near infrared spectroscopy (NIR) would be useful for pulp mills that need to maximize pulp yield without compromising paper strength properties. If models developed from the absorbance at wavelengths in the NIR region could provide density histograms, fiber supply personnel could monitor chip density variation as the chips enter the mill. The objectives of this research were to a) develop density histograms from actual density versus density histograms developed through NIR modeling, and b) determine the precision of density models developed from absorbance in the NIR region with a recommendation for the sample size needed to estimate the standard deviation of density at a given precision.Models for density were developed from calibration samples (n = 170) and then validated with 93 randomly held aside samples. The samples were systematically removed from 10 longleaf pine trees of equal age, but different growth rates. The histogram patterns for actual density almost paralleled the histogram patterns developed from predictive models. Subsequently, the validation data set was randomly categorized into groups of three, and the standard deviations of density were measured. For three measurements per data point, the predicted standard deviation covaried with the actual standard deviation of density with an R2 = 0.61 and 0.55 for the calibration and validation data set, respectively. A sample size of 30 was recommended to estimate the standard deviation of density with a precision of 0.01 g/cm3

Maleated Polypropylene Film and Wood Fiber

The grafting effect of maleic anhydride (MA) as an interfacial bonding agent and its influence on the tensile strength properties of thermomechanical pulp handsheet-isotactic polypropylene (iPP) film laminates was studied. For the MA treated with benzoyl peroxide (BPO) as an initiator, tensile strength properties increased 76 % with PP film over untreated laminates. The optimal strength properties were obtained with a MA and BPO ratio of 2:1. A strong correlation was observed between the number of fibers in the web and tensile strength properties for both handsheet drying conditions. The R 2 values were 0.95 for air-dry conditions and 0.94 from oven-dry conditions. Scanning electron microscopy images also showed the effectiveness of MA loading on the surface of thermomechanical pulp fibers due to increased fiber failure, which occurred without fiber being pulled out from the PP matrixes. Crystallinity and heat flow were determined using differential scanning calorimetry (DSC) and increased as expected as the ratio of MA and BPO increased from 0:0 to 2:1. These results were also in accordance with the morphological observations at the fracture surface, Fourier transform infrared spectra, and thermal analysis. POLYM. COMPOS., 00:000–000, 2008. ª 2008 Society of Plastics Engineer

The Response of Visible/Near Infrared Absorbance to Wood-Staining Fungi

The influence of blue-stain fungi [Ophiostoma minus (Hedgcock) H. and P. Sydow and Leptographium serpens (Goid.) Siemaszko] on absorbance at the visible and near infrared wavelengths was investigated. Forty trees were sampled at breast height from longleaf pine (Pinus palustris Mill.). One half of each increment core was inoculated with one of two fungi treatments while the other half served as a control. Visible and near infrared spectra were acquired between rings 3-40 for the stained and control-clear wood samples (n = 304). Absorbance was greater for the stained than the control wood at wavelengths between 464 to 1334 nm. Statistical techniques were applied to the NIR data to determine which wavelengths, and their corresponding chemical assignments, were most affected by the fungi. First and 2nd derivative pretreatments to the original spectra resulted in some blue-stain sensitive wavelengths throughout the 350 to 2500 nm range, some of which are associated with nitrogen in the melanin present in blue stain. However, for the 2nd derivative pretreatment, the stained wood exhibited a different signal to noise ratio than the control wood, and thus the pretreatment method should be used with vigilance. For the raw, 1st, and 2nd derivatives, the absorbance of L. serpens (n = 164) significantly differed from O. minus (n = 140) between 424-554 nm. The results of this study are important because the absorbance at visible and NIR wavelengths may be used to classify stained wood

From atoms to bonds, angles and torsions: molecular metrics from crystal space, and two Excel implementations

Values of molecular bond lengths, bond angles and (less frequently) bond torsion angles are readily available from databases, from crystallographic software, and/or from interactive molecular and crystal visualization programs such as Jmol. However, the methods used to calculate these values are less well known. In this paper, the computational methods are described in detail, and live Excel implementations, which permit readers to readily perform the calculations for their own molecular systems, are provided. The methods described apply to both fractional coordinates in crystal space and Cartesian coordinates in Euclidean space (space in which the geometric postulates of Euclid are valid) and are vector/matrix based. In their simplest computational form, they are applied as algebraic expansions which are summed. They are also available in matrix formulations, which are readily manipulated and calculated using the matrix functions of Excel. In particular, their general formulation as metric matrices is introduced. The methods in use are illustrated by a detailed example of the calculations. This contribution provides a significant practical application which can also act as motivation for the study of matrix mathematics with respect to its many uses in chemistry