Reliability Indices for Bolted and Nailed Connections in Wood Structures

Recently published test data for bolted and nailed connections was evaluated to assess the structural reliability inherent in current allowable stress design procedures for connections in wood structures. Reliability indices were determined for timber connections using standard firstorder, second moment (FOSM) procedures. For the connections considered in this study, reliability indices range from 2.6 to5.1, generally providing higher levels of safety than the structural members in timber structures

Localized Tensile Strength and Modulus of Elasticity of E-Related Laminating Grades of Lumber

Localized modulus of elasticity (MOE) and tensile strength (T) of six E-rated grades and two visual grades of 2 by 6 Douglas-fir laminating lumber were measured over a test span of 2 ft. The E-rated laminating grades studied were C14, 2.3E-1/6, 2.3E-1/3, 2.0E-1/6, 2.0E-1/3, and 1.7E-1/4. The visual laminating grades were L2 and L3, which consisted of lumber not qualifying for the E-rated grades. Multivariate statistical parameters and probability distributions were fit to the localized MOE and T data. These parameters can be used to simulate lumber properties needed to predict the reliability of glued-laminated timber beams. Localized MOE and T data were simulated using a multivariate approach to determine whether the statistical properties of the original MOE and T data were preserved in the simulated data. The original statistical properties (i.e., probability distributions and correlations) were preserved in the simulated data for all lumber grades studied

Shear Deflection of Composite Wood Beams

Shear deflection of wood beams usually is not included in design calculations. Ignoring shear deflection could lead to significant errors in total beam deflection predictions, especially for composite wood beams that have less and/or lower quality material in the core (or web) as compared to the outer zones (flanges).A generalized shear deflection equation was developed for layered composite beams. The model can accommodate variable numbers of laminations, nonprismatic shapes, and variable elastic properties between laminations and along the beam length. The model was validated using full-sized glued-laminated timber beam test data. Sensitivity analyses were conducted on numerical integration step sizes, ratio of modulus of elasticity to shear modulus, and span-to-depth ratio (L/d). One important finding was that the common engineering design practice of not including shear deflection for solid-sawn wood beams with L/d ratios of 15 to 25 could lead to significant errors for composite wood beams

Effect of Tie-Layer on the Bond Strength Between Thermoplastic and Borate-Treated Wood Substrate

A challenge in using wood or wood composites for exterior applications is durability. Borate-treated wood substrates are durable if leaching of the chemical over time can be reduced to acceptable levels. The goal of this project was to encapsulate borate-treated structural wood and wood-based composites with thermoplastic to extend their durability. In this study, the efficacy of two tie-layers (maleic anhydride modified high-density polyethylene and styrene-butadiene polymer) in bonding high-density polyethylene (HDPE) to treated wood substrate was examined together with determining the ideal hot-press parameters necessary to achieve a good bond. Boric oxide treated Douglas-fir and southern pine Parallam® and untreated Douglas-fir solid wood were the substrates investigated. The optimum processing parameters were 180°C platen temperature, 1035 kPa press pressure, and 300 s press time. Bond strength was determined by conducting a 90° peel test and a block-shear test. Durability of the thermoplastic barrier layer was evaluated by subjecting specimens to an accelerated aging test and reevaluating the bond strength. Maleic anhydride-modified HDPE tie-layer yielded improved bond strength that was durable, especially when bonded to a treated southern pine substrate

Nitrogen phosphorus and carbox flux in Chesapeake Bay marshes

Annual nitrogen, phosphorus and carbon budgets for two Virginia salt marshes were determined .by monthly measurements of water discharge and constituent concentrations over tidal cycles. Considering all three forms of phosphorus measured (total, dissolved organic and orthophosphate) there was a net loss from the estuary to the marches. The data reveal a loss of particulate phosphorus of estuarine origin to marsh sediments and mineralization of this phosphorus in the marshes with subsequent export of dissolved inorganic and organic phosphorus back to the estuary. Nitrogen flux data show a loss of nitrate and nitrite to the marshes. Particulate nitrogen is imported to the marshes where it is mineralized and returned to the estuary as ammonia and dissolved organic nitrogen. The magnitude of nitrogen export suggests significant fixation of atmospheric nitrogen by marsh flora with subsequent export as dissolved species. Carbon flux data show significant contributions of both particulate and dissolved organic carbon to the estuary from the marshes. Estimates of export, based on marsh grass productivity, suggest a loss of 36 and 49 percent of a year\u27s primary production on the marshes as detritus for Ware and Carter Creeks respectively

A Critical-Angle Ultrasonic Technique for the Inspection of Wood Parallel-to-Grain

The objective of this paper is to present a critically refracted longitudinal wave (LCR) technique that allows localized ultrasonic inspection of wood parallel-to-grain by accessing only a single side of the material. The LCR technique has been widely applied to other materials, but not to wood. The chief advantage of the LCR technique is that ultrasonic waves can be transmitted through wood at frequencies much higher than previously possible (up to 1.5 MHz), leading to potential gains in sensitivity over lower frequency methods.The LCR technique was verified using southern pine lumber. Transducer beam characteristics were examined and the influence of growth ring angle was observed. Ultrasonic wave energy was found to travel near to the inspection surface. Further, localized growth ring angle was significantly correlated to signal amplitude and frequency

Ultrasonic Detection of a Plastic Hinge in Bolted Timber Connections

Connections between structural members are critical elements that typically govern the performance of structural systems; hence, techniques for monitoring the condition of connections are needed to provide early warning of structural damage. Plastic hinge formation in fasteners frequently occurs in timber connections when the yield capacity is exceeded. An innovative pulse echo testing technique was developed for detecting the formation of a plastic hinge in bolted timber connections and estimating the associated magnitude of connection displacement. A shift in overall signal centroid proved to be the best flTedictor of plastic hinge formation, with a coefficient of determination (R2) of 0.9. As the plastic hinge angle increased, the signal centroid shifted to the right since a higher proportion of pulse energy was forced to undergo multiple transverse wave reflections caused by the deformed geometry of the bolt. Because the determination of a shift in signal centroid requires the availability of prior test information for the initially undeformed fastener, an alternate linear relationship between echo amplitude ratios and plastic hinge formation was also proposed with an adjusted R2 of 0.87. This three parameter regression equation had the advantages of requiring no prior testing information and eliminating ambiguity in signal analysis associated with selection of echo start and end points. Plastic hinge formation was correlated with connection ductility, magnitude of connection overload and energy based measures of connection damage to assess residual connection capacity

Ultrasonic Plate Wave Evaluation of Natural Fiber Composite Panels

Two key shortcomings of current ultrasonic nondestructive evaluation (NDE) techniques for plywood, medium density fiberboard (MDF), and oriented strandboard are the reliance on empirical correlations and the neglect of valuable waveform information. The research reported herein examined the feasibility of using fundamental mechanics, wave propagation, and laminated, shear deformable plate theories to nondestructively evaluate material properties in natural fiber-based composite panels. Dispersion curves were constructed exhibiting the variation of flexural plate wave phase velocity with frequency. Based on shear deformable laminated plate wave theory, flexural and transverse shear rigidity values for solid transversely isotropic, laminated transversely isotropic, and solid orthotropic natural fiber-based composite panels were obtained from the dispersion curves. Axial rigidity values were obtained directly from extensional plate wave phase velocity. Excellent agreement (within 3%) of flexural rigidity values was obtained between NDE and mechanical testing for most panels. Transverse shear modulus values obtained from plate wave tests were within 4% of values obtained from through-thickness ultrasonic shear wave speed. Tensile and compressive axial rigidity values obtained from NDE were 22% to 41% higher than mechanical tension and compression test results. These differences between NDE and axial mechanical testing results are likely due to load-rate effects; however, these large differences were not apparent in the flexural and transverse shear comparisons. This fundamental research advances the state-of-the-art of NDE of wood-based composites by replacing empirical approaches with a technique based on fundamental mechanics, shear deformation laminated plate theory, and plate wave propagation theory

Early-type galaxies in the SDSS. I. The sample

A sample of nearly 9000 early-type galaxies, in the redshift range 0.01 < z < 0.3, was selected from the Sloan Digital Sky Survey using morphological and spectral criteria. This paper describes how the sample was selected, presents examples of images and seeing corrected fits to the observed surface brightness profiles, describes our method for estimating K-corrections, and shows that the SDSS spectra are of sufficiently high quality to measure velocity dispersions accurately. It also provides catalogs of the measured photometric and spectroscopic parameters. In related papers, these data are used to study how early-type galaxy observables, including luminosity, effective radius, surface brightness, color, and velocity dispersion, are correlated with one another.Comment: 63 pages, 21 figures. Accepted by AJ (scheduled for April 2003). This paper is part I of a revised version of astro-ph/0110344. The full version of Tables 2 and 3, i.e. the tables listing the photometric and spectroscopic parameters of ~ 9000 galaxies, are available at http://astrophysics.phys.cmu.edu/~bernardi/SDSS/Etypes/TABLE