Transforming a Corner of a Light-Frame Wood Structure to a Set of Nonlinear Springs

The computational efficiency of a full-structure model for a light-frame building is enhanced by replacing the continuum of the detailed connections with rotational and translational nonlinear springs that are energetically equivalent between two bounds. This study examines the transformation from the physical exterior-wall-to-exterior-wall connection (a corner) of a light-frame wood structure, first, to a two-dimensional finite-element model and, then, to a set of nonlinear springs. Typical light-frame details are used as the starting point, and the product is the characteristic moment-rotation and load-displacement relationships for a 24-inch segment of the corner

Comparative Performance of Long-Term Loaded Wood Composite I-Beams and Sawn Lumber

Solid sawn southern pine lumber (2 x 10 and 2 x 12) and wood composite I-beams having machine stress-rated southern pine flanges and composite panel webs (plywood, oriented strand board, and waferboard) were subjected to long-term loading in a stable hygrothermal environment and then destructively tested so that residual load-deflection characteristics could be measured. A 4-element viscoelastic model was fitted to the creep data on a specimen-by-specimen basis. Load history had a minor effect on the stiffness performance of I-beams, but did not influence load capacity or deflection at maximum load. Large variations in the lumber data obscured the subtle effects a load history might impose. Failure modes and locations in destructively tested specimens indicated that load history did not play a role in the ultimate failure mechanism

Deformation of Wood-Based Material During Supercritical Carbon Dioxide Treatment

The deformation of various wood-based materials during supercritical carbon dioxide treatment was assessed in situ at a range of pressurization and venting rates. Deformation was minimal with oriented strandboard (OSB), medium density fiberboard (MDF), and solid Douglas-fir heartwood, and even this slight deformation was rapidly recovered once the pressure was released. Higher degrees of deformation were observed in laminated veneer lumber (LVL) composed of Douglas-fir veneers and this deformation was not completely recovered at the end of the process. The resulting deformation resulted in permanent veneer separations. The results indicate that there is little risk of damage during supercritical carbon dioxide treatment of OSB, MDF, and Douglas-fir heartwood, but that further process studies will be required to identify treatment cycles suitable for treatment of LVL

Applications of Perpendicular-To-Grain Compression Behavior in Real Wood Construction Assemblies

Compression perpendicular to grain (C┴) of wood is an important property and has a drastic effect on serviceability of the structure. Typical C┴ loading scenarios include the bottom chord of a truss resting on the top plate of a shear wall and chords of a shear wall resting on the bottom plate. Present design values for C┴ are based on stress at 1-mm deflection for an ASTM block test. However, in real applications, loading conditions and deflection limits are much different from that administered during the test. There is a need to characterize C┴ behavior of wood in construction applications and compare it with current design codes. This study addresses that by testing two different assemblies involving C┴ loading, each with two different species of wood, to quantify the design C┴ based on the desired application and compare it with current design codes. Also, the effect of species and aspect ratio of assembly was characterized. Results suggested that the ASTM values significantly differ from the assembly values. Species of wood did not have any effect on the performance of the assemblies. A 2% strain offset method was proposed to determine allowable value for C┴ for a desired application. Adjustment factors based on loading configurations were suggested for calculation of design values

Effects of Wood Decay By Postia Placenta on the Lateral Capacity of Nailed Oriented Strandboard Sheathing and Douglas-Fir Framing Members

The effect of wood decay on the single shear strength of nailed oriented strandboard (OSB) sheathing to Douglas-fir framing member connections was investigated. The connections evaluated in this study were representative of those present in lateral force resisting system components of light-framed wood structures, including shear walls and horizontal diaphragms. Strength and stiffness of the nailed connections were characterized using monotonic testing of samples exposed for increasing intervals to the brown rot fungus, Postia placenta. After the destructive tests, portions of the sheathing and framing member from the samples were further evaluated for dowel bearing strength and weight loss. The results indicated that existing yield models used for design of nailed connections can predict nominal design values for nailed connections of OSB sheathing and Douglas-fir framing members with various levels of decay damage, provided that the dowel bearing capacity of the wood materials can be assessed

Sheathing Nail Bending-Yield Stress: Effect on Cyclic Performance of Wood Shear Walls

This study investigated the effects of sheathing nail bending-yield stress (fyb) on connection properties and shear wall performance under cyclic loading. Four sets of nails were specially manufactured with average fyb of 87, 115, 145, and 241 ksi. Nail bending-yield stress and the hysteretic behavior of single-nail lateral connections were determined. The parameters of the lateral nail tests were used in a numerical model to predict shear wall performance and hysteretic parameters. The competency of the numerical model was assessed by full-scale cyclic tests of shear walls framed with Douglas-fir lumber and sheathed with oriented strandboard (OSB). The parameters of the shear wall model were used in another program to predict shear wall performance for a suite of seismic ground motions. The single-nail connection tests and wall model computations suggested that increased fyb of the sheathing nails should lead to improved wall stiffness and capacity. In both single-nail lateral connection and shear wall tests, the probability of nonductile failure modes increased as fyb increased. The peak capacity of the walls increased as fyb of the sheathing nails increased up to 145 ksi, but wall initial stiffness, displacement at peak capacity, and energy dissipation were not significantly affected by fyb. Sheathing nail fyb greater than 145 ksi did not enhance the overall cyclic behavior of wood shear walls

Applications of perpendicular-to-grain compression behavior in real wood construction assemblies

Compression perpendicular to grain (C┴) of wood is an important property and has a drastic effect on serviceability of the structure. Typical C┴ loading scenarios include the bottom chord of a truss resting on the top plate of a shear wall and chords of a shear wall resting on the bottom plate. Present design values for C┴ are based on stress at 1-mm deflection for an ASTM block test. However, in real applications, loading conditions and deflection limits are much different from that administered during the test. There is a need to characterize C┴ behavior of wood in construction applications and compare it with current design codes. This study addresses that by testing two different assemblies involving C┴ loading, each with two different species of wood, to quantify the design C┴ based on the desired application and compare it with current design codes. Also, the effect of species and aspect ratio of assembly was characterized. Results suggested that the ASTM values significantly differ from the assembly values. Species of wood did not have any effect on the performance of the assemblies. A 2% strain offset method was proposed to determine allowable value for C┴ for a desired application. Adjustment factors based on loading configurations were suggested for calculation of design values

Characterizing perpendicular-to-grain compression (C⊥) behavior in wood construction

Current compression perpendicular-to-grain (C⊥) design values for wood members are based on mean stress obtained from ASTM D143 specimen. The standard ASTM test with metal on wood bearing has limited applicability in modern construction assemblies with C⊥ loading scenarios. Previous work has shown that end-bearing conditions and wood-on-wood C⊥ bearing is a more severe case as opposed to load applied over central area and metal-on-wood bearing. This study evaluated C⊥ behavior of typical assemblies used in construction, in which members experience C⊥ stresses near their longitudinal-end through wood-on-wood contact. These included assembly of the bottom chord of a truss bearing on the top plate of a wall (BC assembly) and assembly of the compression chord of a shear wall bearing on the bottom plate (BP assembly) of a wall. Three different BC assemblies were tested with varying aspect ratios (height/width) of the bottom chord (B.C.) member. For each test assembly, paired ASTM tests of the main member (bottom chord member in BC tests, and bottom plate member in BP tests) were conducted. The assembly stresses at 1 mm deflection were always lower than the corresponding ASTM stresses at the same deflection. Due to varying assembly depths, 1 mm deflection was a poor criterion for determining C⊥ stress values. For B.C. members, when loaded tangentially, they buckle in the direction of annual ring curvature. High aspect ratios accentuate this effect. Expectedly, the tendency to buckle and the probability of total failure in the assembly increase with increasing aspect ratio. This behavior was not observed in the ASTM tests

Internal Pressure Development and Deformation During Supercritical Fluid Impregnation of Selected Wood-Based Materials

The effect of supercritical carbon dioxide impregnation on pressure development was assessed on oriented strandboard (OSB), medium density fiberboard (MDF), laminated veneer lumber (LVL), and solid-sawn Douglas-fir heartwood lumber. Pressure differences between the surface and the interior were relatively small with MDF and OSB, owing to the presence of numerous pathways for fluid flow. Pressure differences tended to be higher in LVL and solid wood, but were still below the levels necessary for inducing material damage, except when flow directions were restricted and pressure was rapidly applied. The results indicate that supercritical fluid (SCF) impregnation is suitable for most composites, although care must be taken to limit pressure changes in situations where flow is restricted

Prefabricated Wood Composite I-Beams: A Literature Review

This paper reviews the available literature on the state of the art of prefabricated wood composite I-beams. The results of analytical and experimental investigations illustrate the effects of materials, joint, geometry, and environment on the short- and long-term performance of I-beams