Strength of End-Notched Wood Beams: A Critical Fillet Hoop Stress Approach

An equation for predicting the strength of wood beams with end notches on the tension side (Tension-side End Notches or TEN) was derived using a critical fillet hoop stress (CFHS) theory. The equation combines the results of finite element and statistical analyses of 690 different TEN beam configurations and experimental tests of 362 full-size beams. It accounts for the effects of loading type, end support and beam and notch geometry variables such as beam height, fractional notch depth, radius, and notch location. The effect of span-to-depth ratio is implicit to the model. Notched beam strength is represented by a material parameter, k, which can be obtained from notched beam tests. The equation is applicable to both filleted and sharp-cornered notches. An effective radius, Re, which models the effect of a sharp-cornered notch, was determined and confirmed for two wood materials. A method of determining Rc for other materials was established. The results of this study can be used to set new design criteria for the strength of notched wood beams

Effect Of Gap Size On Performance Of Metal-plated Joints In Compression

Metal-plate splice joints with gaps between butting pieces of 2 x 4 lumber were tested in compression to evaluate the effect of gap size on joint serviceability performance. The current design methodology for compression splice joints was also evaluated. Specimens representing floor and roof truss compression joints, with 16- and 20-gauge plates of staggered and aligned tooth configurations, were tested for each of two gap sizes.Generally, 20-gauge and 16-gauge plates on joints with 1/8 in. nominal maximum gaps buckled under compression loads while 16-gauge plates on joints with nominal 1/16 in. maximum gaps did not buckle before the gap closed. Gap closure with the latter joints was due principally to slip between the teeth nearest the splice and the wood. Joints with 16-gauge plates generally outperformed those with 20-gauge plates, based on the serviceability performance indicators of the test compression splice joints. Furthermore, gap size had less of an influence on joints with 16-gauge plates than on joints with 20-gauge plates.The current practice of sizing plates for compression splices to withstand one-half of the calculated chord force could not be physically confirmed using joint serviceability criteria. The test results indicated that basing allowable plate ratings on a surface-area basis derived from tension tests is misleading

Toughness of Sap-Stained Southern Pine Salvaged After Beetle Attack

Approximately 1,200 small clear specimens were machined from visually graded dimension lumber and tested for toughness. Dimension lumber was obtained from green healthy southern pine and beetle-killed southern pine at various times after foliage fade. The specimens machined from beetle-killed material were free of defects with the exception of sap stain, which is not currently considered in grading rules. Toughness generally decreased with increasing time between foliage fade and the harvesting of the beetle-killed sawtimber. Most of the loss in toughness occurred during the first year after foliage fade. For certain structural applications where toughness or shock resistance of wooden members may be of some importance, caution should be exercised in the utilization of beetle-killed southern pine

Quantitative Wood Anatomy—Relating Anatomy to Transverse Tensile Strength

The tension perpendicular-to-grain properties of eight North American hardwood species were determined and related to their anatomy. Stereological techniques based on countings of points and intersections were used to quantitatively characterize the anatomy of each species. Modulus of elasticity and proportional limit stress values were found to be more dependent on specific gravity than anatomy. However, the properties associated with failure were closely associated with anatomical features. Earlywood vessel area fraction negatively influenced radial maximum stress and strain, whereas the ray width and area fraction were positively related to the maximum radial properties. Analysis showed that the rays significantly affected the transverse stiffness

EXAFS study of nickel tetracarbonyl and nickel clusters in zeolite Y

Adsorption and thermal decomposition of Ni(CO)4 in the cage system of zeolite Y have been studied with EXAFS, electron microscopy and IR spectroscopy , Ni(CO)4 is adsorbed as an intact molecule in both cation - free zeolite Y and NaY. Symmetry changes of the molecule in NaY are assigned to the formation of Na—OC-IMi bridges. Thermal treatment of the Ni(CO)4/NaY adduct leads to loss of CO concomitant with the formation of a binodal Ni phase. A major part of the forms clusters with diameter between 0.5 and about 1.5 nm, in addition to larger crystallites (5-30 nm), sticking at the outer surface of the zeolite matrix., The Ni-Ni scattering amplitude indicates increasing average particle size with increasing temperature

LRFD for Engineered Wood Structures - Connection Behavioral Equations

A new design specification for engineered wood structures has been proposed in load and resistance factor design (LRFD) format. This paper provides an overview of the proposed LRFD connections design criteria. The connections design provisions are, in part, calibrated from allowable stress design provisions. Major changes from historic practice, however, result from a change in behavioral equations to a theoretical base for predicting the lateral strength of connections using bolts, screws, and nails. New provisions for axial withdrawal of driven and turned fasteners, as well as combined axial and lateral loading criteria are also proposed. Safety levels were calibrated to historic practice, but some change in design capacity is expected due to format change, conversion to new behavioral equations. and the selection of a calibration point. The LRFD document contains substantial improvement in code clarity. simplification. and structure over the historic allowable stress specification. A clear mechanism for including design with new wood-based engineering materials is provided

Analysis of Racked Wood Pallets

A rational analysis procedure for designing wood stringer pallets for use in warehouse storage racks was developed for manufacturers and pallet users and is part of a computerized automatic design and analysis program called the Pallet Design System (PDS). The procedure uses simplified analog models of pallets and matrix structural analysis methods to compute the stress and deflection of critical structural elements. Semi-rigid nail joints are modeled as spring elements. Pallets with 2, 3, 4, or 5 stringers and up to 15 deckboards can be analyzed with a variety of load types including distributed and concentrated loads. The strength and stiffness of experimental pallets were compared to predicted values and showed good agreement

Predicting the Effect of Moisture Content on the Flexural Properties of Southern Pine Dimension Lumber

Current procedures for adjusting lumber properties for changes in moisture content are based on trends observed with the mean properties. This study was initiated to develop analytical procedures for adjusting the flexural properties of 2-inch-thick southern pine dimension lumber applicable to all grades and sizes as well as all levels of the cumulative frequency distribution. Equations are derived for adjusting modulus of rupture (MOR), modulus of elasticity (MOE), moment capacity (RS), and flexural stiffness (EI) for changes in moisture content. The best of these equations are significantly more accurate than current procedures for adjusting strength properties (MOR and RS). Because MOE and EI are less affected by changes in moisture content, most of the equations, including the current American Society for Testing and Materials procedure, work well for these properties