Rolling Shear Modulus of Sweetgum Plywood and Unidirectionally Laminated Veneer

Experimentally obtained values of apparent rolling shear modulus and strength of sweetgum 4-ply, 12.7-mm-thick plywood, when the shear forces are applied parallel to the face grain of the plywood, are presented. Also presented are experimental values of true rolling shear modulus (GTR) of unidi-rectionally laminated sweetgum veneer tested in the dry condition. Finally, the experimentally obtained value of the apparent rolling shear modulus of the tested sweetgum plywood was closely predicted using the obtained GTR and GLR values

Composite Plywood with Southern Pine Veneer Faces and Oriented Strand Core from Sweetgum and Southern Pine

Certain mechanical properties and dimensional changes of 1/2 in. composite plywood, fabricated from 1/8 in. southern pine veneer faces and 1/4 in. unidirectionally oriented strand cores were evaluated. Three types of cores were included: (a) 100% southern yellow pine, (b) 100% sweetgum, and (c) a mixture of 50% southern pine and 50% sweetgum. The cores were blended with a liquid phenolformaldehyde resin (6 1/2% solids) and bonded to veneer faces with an extended phenolic glue.Experimental results indicate that the physical and mechanical properties of the composite panels were equal to and, in certain cases, superior to 1/2 in. southern pine CDX plywood and to commercial composite plywood from western species.After comparing the experimental results of the composite panels with similar properties of commercial CDX southern pine plywood, the following conclusion can be drawn: Composite panels similar to those tested are expected to perform satisfactorily all structural functions required by sheathing panels for walls, roofs, and subfloors

Tensile Properties of Loblolly Pine Growth Zones

For the determination of tensile properties of the earlywood or latewood zone of loblolly pine, modified standard ASTM tensile specimens were machined so that the critical sections at mid-length of specimens (2 1/2 inches length of uniform cross section) consisted entirely of either earlywood or latewood. Specimens were tested to failure in both the green and air-dry condition.Specific stress and specific stiffness of latewood in the air-dry condition are more than 50% and 63% higher, respectively, than corresponding values for earlywood. More than one-third of the tensile strength of latewood is attributed to factors other than density. Moisture affects the specific strength of latewood more than the specific strength of early-wood. The moisture effect on specific stiffness is approximately the same for both earlywood and latewood. The property affected most by moisture is the specific stress at proportional limit.Same growth zones were tested by microtome sections of approximately 100 μm in thickness. Maximum tensile properties of any growth zone obtained from microtome sections were approximately one-half of the values obtained for the same zone from modified standard tensile specimens

Flexural Properties of Lumber from a 50-Year-Old Loblolly Pine Plantation

Flexural properties of dimension lumber from a 50-year-old loblolly pine plantation stand were evaluated. The results indicate very impressive visual grade recovery, particularly No. 1, which amounted to about 44% yield. The results also indicate that the overall degrees of compliance of visually graded lumber to standard SPIB requirements of strength and stiffness are 99 and 94%, respectively

Properties of Sheathing-Grade Plywood Made from Sweetgum and Southern Pine

Experimental test results of physical and certain important mechanical properties of commercial CDX southern pine plywood, of all-sweetgum plywood, and of plywood with southern pine faces and sweetgum cores are presented. Experimental results indicate that the mechanical properties of all-sweetgum CDX plywood are better than properties of all-southern-pine CDX plywood. Physical properties of all-sweetgum plywood are approximately equal to those of all-southern-pine plywood. In general, the results suggest that all-sweetgum plywood, bonded with phenolic resin, can perform structurally as good as CDX all-southern-pine plywood sheathing in house construction.It is recommended that the American Plywood Association undertake tests according to their performance based standards on all-sweetgum plywood panels to verify and certify that such panels meet the criteria of APA rated sheathing and APA rated sturd-I-floor programs

Gluability of Loblolly Pine Earlywood and Latewood1

Adhesive-bond quality of the following growth zone combinations of loblolly pine was evaluated with an epoxy, a resorcinol-formaldehyde, and a phenolic adhesive: latewood to latewood, earlywood to earlywood, and latewood to earlywood. For latewood-to-latewood bonds, the influence of each of two surface treatments—(a) alcohol-benzene solution and (b) sodium hydroxide solution with each of the three adhesives—was also evaluated. Bonds of latewood-to-latewood zones were poor with all adhesives; surface treatments did not improve bond quality. In assemblies of latewood to latewood, the epoxy developed significantly stronger bonds than the resorcinol-formaldehyde. In turn, the resorcinolformaldehyde developed stronger bonds than the phenolic adhesive. In assemblies of earlywood-to-earlywood zones, all three adhesives developed excellent bonds

Hygroscopic Properties and Shrinkage of Southern Yellow Pine Plywood

Five constructions of southern yellow pine plywood, unidirectionally laminated veneer, and loblolly pine solid wood were used for investigation of hygroscopic properties at several RH conditions. EMC values of the southern yellow pine plywood between 20% RH and 90% RH were approximately 1% lower than corresponding values of loblolly pine solid wood. Most plywood panels shrank less along the face grain than across. From water-soaked condition to about 4.5% MC, thickness shrinkages of plywood varied from 7% to 9% while length shrinkages were always less than 1% except for 1/2-inch, 4-ply plywood. The ratio of number of glue lines to plywood thickness influenced thickness and volume shrinkage. Plywood with a higher ratio had a tendency to shrink less. FSP values were determined by two intersection point methods-one with volumetric shrinkage, the other with MOE. The respective approximate FSP values were 28.7% and 27.3% MC for plywood, and 31.0% and 27.5% for solid wood

An Analysis of Flexural Stiffness of 5-Ply Southern Pine Plywood at Short Spans Parallel to Face Grain

A method for predicting deflection of 5-ply plywood strips in small span-to-depth ratios has been verified experimentally. This method first transforms the cross section of 5-ply plywood into a homogeneous double-I-beam and then calculates shear deflection by equating the internal work with the external work of the bend double-I-beam. This method predicts shear deflection with an average error of 18% and total deflection at span-to-depth ratio of 24:1 with an average error of less than 6%. After considering the nonhomogeneity of southern pine veneer and the deviation of the plywood from the assumed ideal structure, the agreement between predicted and observed total deflection should be regarded satisfactory, particularly in the absence of another method by which deflection can be predicted more accurately. From the above method a simpler equation has been derived and experimentally verified for predicting shear deflection. This simpler equation is based on the assumption that shear deflections in any two beams of the same length, height, and moment of inertia, similarly loaded, are proportional to the summations of the shear stresses on their respective vertical sections

Flexural Properties of Lumber from Two 40-Year-Old Loblolly Pine Plantations with Different Stand Densities

The effects of stand density on the flexural properties and compliance-to-grade requirements of lumber from two 40-year-old loblolly pine plantations were evaluated. The results indicate that stand density is positively influencing the flexural stiffness and grade compliance of the lumber produced from these plantations. On the other hand, stand density had no effect on the flexural strength of the lumber from these plantations. The lumber from the denser 40-year-old stand, which had 28 m/50 yr site index, 2.4-by 2.4-m original spacing, never thinned, with 679 trees/ha and 11.4-sq m basal area at harvest, has 96% and 66% compliance to required flexural strength and stiffness values, respectively. The lumber from the thinned 40-year-old stand, with 28 m/50 yr site index, 2.4-by 2.4-m original spacing, thinned at age 25, with 450 trees/ha and 10.2-sq m basal area at harvest, has 96% and 53% compliance to required flexural strength and stiffness values, respectively. It is now evident from the results of these studies that even dense stands must be older than 40 years of age before they can be harvested for lumber production to ensure attainment of at least 95% lumber grade compliance, i.e., strength and stiffness values that are consistent with assigned visual grades

Comparison of Certain Structural Properties Among 3-Ply, 4-Ply and 5-Ply, 1/2-Inch Southern Pine Plywood Sheathing

An evaluation of three constructions 3-ply, 4-ply and 5-ply, 1/2-inch-thick southern yellow pine plywood sheathing as subfloor and roof was made. The evaluation considered only flexural properties, panel shear properties and dimensional stability in relation to panel cost, though other properties are recognized as being important too.Among the three constructions considered, the 3-ply can support higher flexural loads and deflect less as subflooring than can the 4-ply and 5-ply constructions when panels used with face grain orientation parallel to span (perpendicular to the direction of joists). Specifically, at 16-inch spans, flexural strength and stiffness of 3-ply panels are approximately 8% higher than those of 4-ply panels while the manufacturing cost of 3-ply plywood is approximately 5-8% less than the manufacturing cost of 4-ply.Although the 3-ply construction exhibits significantly larger dimensional changes than the two other constructions, it appears that would not create any trouble if used as sub-flooring, since changes of moisture conditions in modern housing are not large enough to produce appreciable internal stresses