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Test method comparison of shear modulus evaluation of MSR and SCL products.

Abstract

Structural composite lumber (SCL) has become a common material in the construction industry and is a practical alternative for solid-sawn lumber. As research on SCL products continues to grow, interest has arisen in measuring the elastic properties of these materials, especially the in-plane shear modulus. Shear modulus terms are used in calculations of shear deflection, torsion, lateral buckling, and fracture mechanics. Currently, there is no single test standard for the shear modulus determination of SCL materials. This research compared the ASTM D 198 three-point bending test, ASTM D 198 torsion test and the five-point bending test (FPBT) using sequentially evaluated LVL and MSR lumber for in-plane shear modulus, [G.sub.12]. For the LVL material, the [G.sub.12] values from all three tests were significantly different. For the MSR material, the three-point bending and FPBT [G.sub.12] values were not significantly different, while the torsion test [G.sub.12] was significantly different. This finding is in contrast to assumptions made in the ASTM D 198 test standard, where shear modulus results from torsion and three-point bending are assumed equivalent. The authors recommend that the choice of an appropriate shear modulus test should mimic the expected loading of the members under study. The authors also recommend that current bending loading tests attain a minimum of 40 percent shear deflection to ensure lower COV values of the shear modulus results.

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Structural composite lumber (SCL) has proven to be a useful and popular alternative to solid-sawn lumber. The use of SCLs in light frame construction has increased substantially in recent years. These building materials not only possess the advantage of being manufactured from smalldiameter timber, but also have enhanced strength and stiffness properties in comparison to their solid-sawn counterparts. Questions have arisen about the applicability of current solidsawn lumber mechanical property test methods applied to SCL materials.

Presently, the testing methods used to evaluate the material properties of structural sized engineered wood composites are identical to those used for solid-sawn wood. Though SCL products are evaluated according to their own standard, ASTM D 5456, Standard Specification for Evaluation of Structural Composites Lumber Products (ASTM 2004a), the test methods listed in this standard largely reference those listed in ASTM D 198, Standard Test Methods of Static Tests of Lumber in Structural Sizes (ASTM 2004b). Of particular interest are the test methods to determine the in-plane shear moduli of both solid wood and wood-based composites. However, no specific guidelines for evaluating this material property are mentioned in ASTM D 5456 (ASTM 2004a).

The in-plane shear modulus of wood materials is useful in the calculation of shear deflection, torsional rigidity, lateral torsional buckling, and for fracture mechanics applications. However, differences among shear moduli test methods used by various researchers have produced different shear modulus values. In particular, the present shear moduli data for SCLs has proven inadequate in the design equations for lateral torsional stability and torsional rigidity (Hindman et al. 2005a and 2005b).

A better understanding of the shear moduli of SCLs would improve the predictive power of such design equations while also allowing for the use of these products in more demanding structural applications. The standardization of a single test method would also allow for a more consistent measurement of shear modulus. Currently, ASTM D 198 offers two test methods to compute the shear modulus, a three-point bending test and a torsion test, while a third possibility, the five-point bending test, has been used for shear modulus evaluation by previous authors (Bradtmueller et al. 1998, Hindman et al. 2006).

Background

Many researchers have conducted shear modulus tests on structural sized materials. Table 1 shows the results of shear modulus of testing upon structural size solid-sawn lumber and SCL materials. Doyle and Markwardt (1966) performed shear modulus evaluation of southern pine lumber using a method similar to the ASTM D 198 (2004b) torsion test. No specific shear modulus from Doyle and Markwardt (1966) is given in Table 1 because of the range of sizes (2 by 4, 2 by 6, 2 by 8) and grades (No. 1, No. l Dense, No. 2, No. 2 Dense, No. 3) evaluated. However, summary tables provide the average E:G ratio. Bodig and Goodman (1973) performed extensive shear modulus testing of different species of wood using a plate twisting method with accompanying plate bending to measure the modulus of elasticity. This testing included all three orthotropic shear moduli, which were generated by the use of laminated plates. The [E.sub.L]:[G.sub.LR] ratios from the different species tested ranged from 4.8:1.0 to 26.1:1.0. While the wood material tested was not of structural size, the results from this testing are widely recognized as the basis for the assumption of the E:G ratio of 16.0:1.0 for solid-sawn lumber used in the Wood Handbook (USDA 1999) as well as the National Design Specification for Wood Construction (AF&PA 2001).

More recent testing of solid-sawn lumber has included evaluations using the current ASTM D 198 (2004a) bending procedure (Palka and Barret 1985 and Hindman et al. 2006). Palka and Barrett (1985) conducted a study in order to investigate the effect of the span-to-depth ratio. Hindman et al. (2006) compared shear modulus values for solid-sawn lumber and various SCL materials using both the ASTM D 198 (2004b) bending procedure and the five-point bending test (FPBT). The FPBT has been suggested by several authors (Hunt et al. 1993, Bradtmueller et al. 1994) as a test method useful for shear modulus determination.

ASTM D5456 (2004a) Standard Specification for Evaluation of Structural Composite Lumber Products is the present test method for the evaluation of material properties of SCLs, but no specific information about the evaluation of shear modulus is given in this standard. However, ASTM D 5456 (2004a) references ASTM D 198 (2004b), thus leading the reader to assume that the test methods listed in ASTM D 198 (2004a) can also be applied to SCL materials. In the same study cited previously for solid-sawn lumber, Hindman et al. (2006) measured the shear modulus of southern pine LVL using the ASTM D 198 (2004b) bending procedure and the FPBT. Bradtmueller et al. (1998) used the FPBT for southern pine LVL.

The range of E:G ratios measured for solid-sawn lumber range from 8.7:1.0 to 20.9:1.0. This is a large range of E:G ratios which could lead to nonconservative design results ifa proper ratio is not chosen (Hindman et al. 2005a). The range of E:G ratios measured for southern pine LVL is much less (19.6:1.0 to 23.5:1.0), but this still represents a 16.5 percent difference from the largest to smallest value. The results of E:G ratio comparison are further confounded by the use of different test methods for shear modulus evaluation. An overall decision to use one consistent test method or to further refine the current test methods may help to decrease the variability of measured shear modulus values.

The goal of this research is to compare test methods used to measure the shear modulus of both solid-sawn lumber and SCL materials. This research will evaluate only structural size members to represent the shear modulus values that would affect the properties of wood sections in use. The specific objectives include:

1) Measure the shear moduli of MSR lumber and LVL using ASTM D 198 (2004a) three-point bending, ASTM D 198 (2004b) torsion and the five-point bending test (FPBT). The test methods of three-point bending and the FPBT also include evaluation of the elastic moduli.

2) Compare the elastic and shear moduli values derived from each test method.

3) Compare the experimentally measured E:G ratios to the standard ratio of 16.0:1.0 assumed for solid-sawn lumber.

4) Based on the results of the previous objectives and assessment of the test data, recommend the most appropriate test method for shear moduli determination.

Methods and materials

Test specimens included a set of 1.9E southern pine LVL specimens and a set of 2400f-2.0E MSR southern pine lumber. Material of nominal 2 by 8 size (3.8 cm by 19.1 cm (1.5 in by 7.5 in)) was chosen to satisfy the [(h/L).sup.2] ratio requirements of the ASTM D 198 (2004b) three point bending test. All specimens were a minimum of 3.66 m (12 ft) long because of limitations of the torsion testing apparatus. Specimens were stored in the Wood Engineering Laboratory at Virginia Tech for approximately 1 month prior to testing to reduce moisture variation between samples. After all testing was completed, samples were cut from each specimen to measure moisture content (MC) and specific gravity (SG) using ASTM D 2395 (2004c).

The test methods used in this research included ASTM D 198 (2004b) (both three-point bending and torsion testing) and the FPBT for shear modulus determination. To provide a direct comparison between the three test methods, all specimens were tested under each of the three shear modulus evaluation protocols. First, the specimens were evaluated using ASTM D 198 three-point bending test. Next, the specimens were evaluated using the ASTM D 198 torsion test. Finally, the specimens were evaluated using the FPBT. After completion of the torsion test, three randomly selected specimens were retested according to the three point bending test at the 3.05 m (10 ft) span. A paired t-test ([alpha] = 0.05) of the load deflection before and after the torsion test was conducted to ensure no permanent damage was inflicted to the specimens. After the FPBT was conducted, three randomly selected specimens were retested according to the three point bending test at the 3.05 m (10 ft) span with an accompanying paired t-test. Statistical comparisons found no difference in the testing results before and after sequential tests; therefore, the shear moduli values from the three tests can be compared.

Flexural test methods

All bending specimens were tested in edgewise bending to determine [E.sub.1] and [G.sub.12] properties. When testing LVL in the edgewise orientation, the geometric and orthotropic axes are aligned, and therefore measured shear properties corresponded solely to the 1-2 orientation. However, for the MSR lumber, this alignment would require perfectly flatsawn or quartersawn pieces of lumber. Such an occurrence is a rarity, and therefore the labeling of the [G.sub.12] shear modulus for solid-sawn lumber is more of a relative measurement.

Bending tests in the edgewise orientation required the use of lateral restraints. The use of at least one lateral restraint approximately halfway between the supports and loading head was required per ASTM D 198 (2004b) recommendations. Lateral restraints were covered in high density polyethylene (HDPE) to eliminate as much friction as possible. All flexural test specimens were loaded to no more than 60 percent of the allowable stress design (ASD) value on a 245 kN (55,000 lb) capacity servo-hydraulic MTS universal testing machine. A load cell with a capacity of 22.2 kN (5000 lbs) and sensitivity of 220 N (50 lb) was used for all load measurements. Deflection measurements were made relative to the neutral axis of the beam with an LVDT with a 5.08 cm (2 inch) range and 0.0254 mm (0.001 in) sensitivity. All load-deflection data were processed using Labview[TM] 7 Express data acquisition software.

ASTM D 198 three-point bending test

The three-point bending test is currently the ASTM standard flexural test for shear modulus determination of wood. This test method specifies that a beam is tested via centerpoint loading over a multiple (minimum of four) spans per specimen. Figure 1 illustrates the testing configuration specified by ASTM D 198 three-point bending.

[FIGURE 1 OMITTED]

A total of five successive spans were used to comply with ASTM D 198 (2004b) requirements. The tested spans were chosen to provide [(h/L).sup.2] ratios within the permissible range of 0.035 to 0.25. Spans were selected to provide values throughout the range of [(h/L).sup.2] ratio recommended. A loading rate of 0.64 cm/min (0.25 in/min) was used for all three-point bending tests. The different spans were tested sequentially beginning with the longest span. After all specimens at the longest span were tested, the supports were repositioned for the next span until testing was completed. Three loading repetitions were used to collect the load-deflection data from each specimen. The average apparent modulus of elasticity was calculated using the following equation.

[E.sub.f] ([P/[DELTA]) [L.sup.3].sub.48I [1]

where,

[E.sub.f] = apparent modulus of elasticity

L = span

I = moment of inertia

P/[DELTA] = slope of the load-deflection curve

These values were plotted vs. corresponding [(h/L).sup.2] ratios to obtain the modulus of elasticity and shear modulus for each specimen.

1/[E.sub.f] = 1/E + 1/KG [(h/L).sup.2]

where,

[E.sub.f] = apparent modulus of elasticity;

E = modulus of elasticity;

K = shape factor (5/6 for rectangular beams);

G = in-plane shear modulus;

h = height of the beam;

L = span of the beam.

Five-point bending test

The FPBT method requires two consecutive flexural loading configurations per specimen, a quarter-point loading and a five-point loading (Fig. 2). Using the load-deflection data from these two loadings, the modulus of elasticity and shear modulus can be solved for simultaneously (Bradtmueller et al. 1994).

[FIGURE 2 OMITTED]

The quarter-point test configuration measured deflection at the center of the beam using a single yoke, while the five-point test configuration measured deflection at the quarter-points using two separate yokes per recommendations by Bradtmueller et al. (1998). The shear span used for edgewise loading was 137 cm (54 in), which allowed for a minimum shear deflection of 40 percent in the five-point loading as recommended by Bradtmueller et al. (1994).

A loading rate of 0.64 cm/min (0.25 in/min) was used for the quarter-point loading, while a slower rate of 0.32 cm/min (0.125 in/min) was used for the five-point loading to ensure adequate data acquisition. The average inverse slopes of the load-deflection data collected from three repetitions for the quarter-point and five-point loadings were used to solve for the modulus of elasticity and shear modulus.

[[DELTA].sub.QP] = 11P[L.sup.3]/96EI + PL/4KGA E = 249[L.sup.3]/{4096I[73/128 [Y.sub.QP] - [Y.sub.FP]]} [3]

[[DELTA].sub.FP] = 7P[L.sup.3]/1536EI + 73PL/512KGA G = 747L/{5632KA[[Y.sub.FP] - 7/176 [Y.sub.QP]]} [3]

where,

P = applied load;

G = shear modulus;

E = modulus of elasticity;

I = moment of inertia;

K = shape factor (5/6 for rectangular sections);

A = cross sectional area;

L = five-point span or one-half the quarter-point span;

[[DELTA].sub.QP] = deflection of quarter-point bending;

[[DELTA].sub.FP] = deflection of five-point bending.

ASTM D 198 torsion

ASTM D 198 (2004b) torsion testing was conducted using a MTS universal testing machine torsion actuator with torque cell 22.2 kN (50,000 in-lb range) and end grip as illustrated in Figure 3. The specimen length between the grips was 3.44 m (135.5 in). The actuator and end grip were both bolted to the laboratory floor to eliminate any change in gage length during testing. ASTM D 198 (2004b) requires symmetrical angular deflection measurements be taken as far apart as possible along the length of the specimen. Two Accustar[R] II/DAS 20 Dual Axis Clinometers with a 20 degree range, [+ or -] 0.01 degrees were positioned 50.8 cm (20 in) from each end with a gage length (DL) of 2.42 m (95.5 in).

[FIGURE 3 OMITTED]

The loading rate recommended by ASTM D 198 (2004b) was 0.092 degrees/cm/min (0.2325 degrees/in/min). Given a gage length of 2.43 m (95.5 in), this recommendation corresponds to a loading rate of 22.2 degrees per minute. Because of the possibility of this loading rate inflicting strain beyond the proportional limit and the inadequacy of data acquisition over such a short time interval, the loading rate was modified from the ASTM D 198 (2004b) provisions. Previous testing using the torsion actuator demonstrated that angular deflections of 7 degrees are within the elastic range of test specimens. Thus, a loading rate of 3.5 degrees per minute was chosen, with the upper limit of rotation being 7 degrees. Three loading repetitions were used to measure the torque-angle curve to calculate the apparent shear modulus according to:

G= (T/[theta]) 16L/[bh.sup.3][(16/3]) - [lambda] (h/b)] [5]

where

G = shear modulus; L = gage length of member

T/[theta] = slope of the torque-angle curve;

b = width of specimen

h = height of specimen

[lambda] = St. Venant constant, Table X3.2, (ASTM 2004b

Results and discussion

The average MC of LVL was 4.9 percent with a coefficient of variation (COV) of 6.3 percent. The average MC of MSR lumber was 5.8 percent with a COV of 4.1 percent. The average SG of the LVL specimens was 0.67 with a COV of 2.4 percent, while the average SG of the MSR specimens was 0.62 with a COV of 9.1 percent. The SG of LVL was expected to be higher than the MSR because of the presence of adhesive bondlines between the veneer layers.

Table 2 shows the modulus of elasticity and shear modulus from experimental testing. The modulus of elasticity values from the LVL testing were 19.6 GPa from the ASTM D 198 Bending and 20.1 GPa from the FPBT, a difference of about 2.5 percent. The modulus of elasticity values from the MSR lumber were 17.4 GPa for the ASTM D 198 Bending and 17.5 GPa from the FPBT, a difference of about 0.6 percent. The modulus of elasticity values measured from the ASTM D 198 and FPBT show very consistent results. The modulus of elasticity results for LVL material also agree well with previous results from Hindman et al. (2006) and Bradtmueller et al. (1998) shown in Table 1. The COV values associated with the modulus of elasticity range from 9.6 percent to 16.2 percent, which are considered normal or slightly low for solid-sawn lumber and SCL (USDA 1999).

Unlike the modulus of elasticity trends, the shear modulus values do not show the same similarity. For the LVL, the shear modulus values were 0.724 GPa from ASTM D 198 Bending, 1.04 GPa from ASTM D 198 Torsion and 1.24 GPa from FPBT. For the MSR lumber, the shear modulus values were 0.903 GPa from ASTM D 198 Bending, 1.16 GPa from ASTM D 198 Torsion and 0.789 GPa from FPBT. For EVE, the ASTM D 198 Bending value is approximately 58 percent of the FPBT value.

The COV expressed in Table 2 shows different trends for different test methods. The COVs associated with the ASTM D 198 Torsion test were below 10 percent (3.5% for LVL and 7.5% for MSR), while the COVs for the FPBT were below 25 percent (14.2% for LVL and 24.1% for MSR). The COVs of the ASTM D 198 Bending test were very large (36.3% for EVE and 56.0% for MSR). These higher COVs may have been caused by the use of multiple spans for the linear regression of the elastic properties.

Table 3 shows the results of an analysis of variance (ANOVA) statistical test conducted upon the modulus of elasticity and shear modulus data obtained from the different test methods. Factors used in the ANOVA included the test method as well as specimen number due to the set of matched specimens used for testing. The modulus of elasticity results, which only compared the ASTM D 198 Bending and FPBT values, had p-values greater than the alpha of 0.05, indicating no significant difference was found. The shear modulus results, which compared results from all three tests, had p-values lower than the alpha of 0.05, indicating a significant difference was found.

The modulus of elasticity and shear modulus results can also be formed into E:G ratios for comparison with previous literature. Table 4 shows the E:G ratios from the experimental data as well as comparisons to an E:G of 16.0:1.0 and comparisons to the ASTM D 198 Bending value. Table 4 shows large differences in the E:G ratios for the different test methods. These differences can be attributed almost entirely to the shear modulus values, given the consistency of the modulus of elasticity values reported in Table 2. The only trend of the test methods consistent between the two materials is that the ASTM D 198 Torsion E:G ratio is less than the ASTM D 198 Bending E:G ratio.

Given the differences in the shear modulus values from the different test methods, the question arises of which value an engineer should choose for computations. Janowiak et al. (2001) suggested that the choice of test method used for elastic constant determination should mimic the intended end-use loading (i.e., use a torsional test value when torsion will occur, or a bending test value when bending will occur). Based on the experimental data observed, there are differences in the shear modulus values evaluated from different test methods. The differences in shear modulus values may be due to inherent test bias present.

Another qualification to determine the appropriate shear modulus value is the lowest variability or COV observed in testing. Clearly, the ASTM D 198 Torsion test has the lowest variability of the three methods tested. Torsion is also considered a theoretically pure state of shear stress (Cook and Young 1985). In observing the evaluation tests of other properties (axial, shear and bending loadings), great care is taken to isolate only the stress field in question, rather than a combined stress condition such as is observed when shear deflection is measured during bending.

The shear stress fields that result from torsion and bending loadings are not consistent, with the shear stress of torsion concentrated around the faces of the beam and the shear stress of bending concentrated at the neutral axis (Cook and Young 1985). Wood itself is only marginally considered a homogenous material, but LVL contains a graduated layup of veneers with veneers of lower stiffness located at the center of the beam and veneers of higher stiffness at the outer edges of the beam. Therefore, for wood composites, there is no real expectation that shear modulus values from bending and torsion should be equivalent. Therefore, the authors recommend that the choice of test method for shear modulus determination remain dependent upon the expected end-use of the material. In cases where the state of stress is unsure or possibly may be combined, further analysis may be needed to predict a conservative value.

The authors also noted a trend in the change of COV that related to the percentage of shear deflection present in the samples. Table 5 shows the relationship between the percentage of shear deflection vs. the COV value from the shear modulus terms for each material and test method. As the percentage of shear deflection present in the specimen increases, the shear modulus COV decreases to a minimum value (ASTM D 198 Torsion) of less than 10 percent. As the amount of observable shear deflection increases in the specimen, the evaluation of the shear modulus term becomes less variable. For the most accurate results, Bradtmueller et al. (1998) prescribed that the five-point loading span be chosen to ensure that at least 40 percent of total deflection be attributable to shear deflection. The authors believe that applying this recommendation to the ASTM D 198 Bending test would produce more consistent results.

Conclusions

This research has demonstrated that the shear modulus values determined from the three test methods are not equivalent. The two methods of shear modulus evaluation referenced in ASTM D 198 (2004b), namely three-point bending and torsion, do not produce similar values. The E:G ratios measured from LVL and MSR materials did not correspond to the commonly assumed value of 16.0:1.0 for solid-sawn lumber. The authors recommend that the choice of shear modulus test method should mimic the expected loading upon the member. From test observations, the COV associated with the shear modulus decreases as the percentage of shear deflection present in the test set-up increases. Therefore, the authors feel that flexure tests for shear modulus evaluation should contain a minimum of 40 percent shear deflection to ensure accurate results.

Literature cited

American Forest and Pap. Assoc. (AFandPA). 2001. Allowable Stress Design (ASD) Manual for Engineered Wood Construction. AFandPA. Washington, D.C. 124 pp.

American Soc. for Testing and Materials (ASTM). 2004a. Standard Test Methods of Static Tests of Lumber in Structural Sizes. Standard D 19899. Annual Book of ASTM Standards, Section 4, Vol. 04.10 Wood. ASTM, West Conshohockcn, Pennsylvania.

--. 2004b. Standard Test Methods for Specific Gravity of Wood and Wood-Based Materials. Standard D 2395-03. Annual Book of ASTM Standards, Section 4, Vol. 04.10 Wood. ASTM, West Conshohocken, Pennsylvania.

--. 2004c. Standard Test Methods for Specific Gravity of Wood and Wood-Based Materials. Standard D 2395-02. Annual Book of ASTM Standards. Section 4, Volume 4.10 Wood, ASTM, West Conshohocken, Pennsylvania.

Bodig, J. and J.R. Goodman. 1973. Prediction of elastic parameters for wood. Wood Sci. 5(4):249-264.

Bradtmueller, J.P., M.O. Hunt, and S.R. Shook. 1998. Mechanical properties of laminated veneer lumber via five-point bending test. J. of Testing and Evaluation 26(2): 132-137.

--, M.O. Hunt, K.J. Fridley, and G.P. McCabe. 1994. Development of the five-point bending test to determine shear moduli of wood composites. Forest Prod. J. 44(5): 17-26.

Cook, R.D. and W.C. Young. 1985. Advanced Mechanics of Materials. Prentice Hall. Upper Saddle River, New Jersey. 539 pp.

Doyle, D.V. and L.J. Markwardt. 1966. Properties of southern pine in relation to strength grading of dimension lumber. Res. Pap. FPL-64. USDA, For. Serv., Forest Prod. Lab. Madison, Wisconsin. 62 pp.

Hindman, D.P., H.B. Manbeck, and J.J. Janowiak. 2005a. Measurement and prediction of lateral torsional buckling of composite wood materials: Rectangular sections. Forest Prod. J. 55(9):42-47.

--, --, and --. 2005b. Torsional rigidity of rectangular wood composites. Wood and Fiber Sci. 3(2):292-303.

--, J.J. Janowiak, and H.B. Manbeck. 2006. Comparison of ASTM D 198 and five-point bending for elastic constant ratio determination. Forest Products J. 56 (7-8):85-90.

Hunt, M.O., S.R. Shook, and J.P. Bradtmueller. 1993. Longitudinal shear strength of LVL via the five-point bending test. Forest Prod. J. 43(7/ 8):39-44.

Janowiak, J.J., D.P. Hindman, and H.B. Manbeck. 2001. Orthotropic behavior of lumber composite materials. Wood and Fiber Sci. 33(4):580-594.

Palka, L.C. and J.D. Banett. 1985. An examination of E/G values for Canadian spruce lumber. Rept. to ASTM task group investigating the validity of Table 2 of ASTM D 2915-74. Forintek Canada Corp. Rept. on file at ASTM headquarters, West Conshohocken, Pennsylvania.

USDA Forest Serv. Forest Products Lab. 1999. Wood Handbook: Wood as an engineering material. Forest Products Soc. Madison, Wisconsin. 463 pp.

The authors are, respectively, Technical Team Leader, Sutton Structurwood[R] Plant, Former WBC GP-Resins Fellow, Virginia Tech, Blacksburg, Virginia (Kate.Harrison@Weyerhaeuser.eom) and Assistant Professor, Dept. of Wood Sci. and Forest Products, Virginia Polytechnic Inst. and State Univ., Brooks Forest Products Center, Blacksburg, Virginia (dhindman@vt.edu). The authors would like to thank Rigidply Rafters and the Wood Based Composites Center at Virginia Tech for material donations and support for this project. This paper was received for publication in December 2006. Article No. 10278.

* Forest Products Society Member. [C]Forest Products Society 2007. Forest Prod. J. 57(7/8):32-38.
Table 1.--Solid wood and LVL E:G ratios reported by various
researchers.

Material Researcher Test method

Southern pine lumber Doyle and Markwardt 1966 ASTM D 198
 Torsion
Solid wood Bodig and Goodman 1973 Plate bending/
 plate twisting
Clear Western Spruce Palka and Barrett 1985 ASTM D 198
 bending
Southern pine MSR lumber Hindman et al. 2006 ASTM D 198
 bending
Southern pine MSR lumber Hindman et al. 2006 Five-Point
 Bending Test
 (FPBT)
Southern pine LVL Hindman et al. 2006 ASTM D 198
 bending
Southern pine LVL Bradtmueller et al. 1998 FPBT
Southern pine LVL Hindman et al. 2006 FPBT

 Average shear modulus,
Material GPa (psi) E:G ratio (b)

Southern pine lumber N/A 11.7:l.0 (a)
Solid wood N/A 16:1.0 (a)
Clear Western Spruce N/A 8.7:1.0 (a)
Southern pine MSR lumber 0.800 (1.16e5) 20.9:1.0 (a)
Southern pine MSR lumber 0.748 (1.09e5) 21.5:1.0 (a)
Southern pine LVL 0.703 (1.02e5) 22.5:1.0 (a)
Southern pine LVL 0.903 (1.31e5) 20.8:1.0 (a)
Southern pine LVL 0.707 (1.03e5) 23.5:1.0 (a)

(a) E:G ratio is an average of reported values.

(b) The E value used in the E:G ratio was the rated value of 13.8 Gpa
(2.0 x [10.sup.6] psi).

Table 2.--Experimental results from modulus of elasticity and shear
modulus evaluations.

 MOE
Material Test method GPa (psi) COV

LVL ASTM D 198 Bending 19.6 (2.84e6) 12.2
LVL ASTM D 198 Torsion N/A N/A
LVL FPBT 20.1 (2.91e6) 9.6
MSR ASTM D 198 Bending 17.4 (2.53e6) 16.2
MSR ASTM D 198 Torsion N/A N/A
MSR FPBT 17.5 (2.54e6) 15.8

Material SM
 GPa (psi) COV
LVL
LVL 0.724 (1.05e5) 36.3
LVL 1.04 (1.51e5) 3.5
MSR 1.24 (1.80e5) 14.2
MSR 0.903 (1.31e5) 56.0
MSR 1.16 (1.68e5) 7.5
 0.789 (1.41e5) 24.1

Table 3.--Analysis of variance (ANOVA) comparisons of elastic
properties.

Material Elastic property comparison p-value (c)

LVL Modulus of elasticity (a) 0.227
LVL Shear modulus (b) 0.0001
MSR Modulus of elasticity (a) 0.850
MSR Shear modulus (b) 0.001

(a) Modulus of elasticity comparison uses the ASTM D 198 Bending
and FPBT results.

(b) Shear modulus comparison uses the ASTM D 198 Bending, ASTM
D 198 Torsion and FPBT results.

(c) [alpha] = 0.05

Table 4.--Comparison of E:G ratios compared to previous results.

 Experimental
Material Test method E:G ratio

LVL ASTM D 198 Bending 27.1:1.0
LVL ASTM D 198 Torsion 18.8:1.0 (a)
LVL FPBT 16.0:1.0
MSR ASTM D 198 Bending 19.2:1.0
MSR ASTM D 198 Torsion 15.1:1.0 (a)
MSR FPBT 22.2:1.0

 Difference from Difference from
Material E:G = 16:1 (b) ASTM D 198 Bending (c)

 (%)

LVL 69.40 N/A
LVL 17.50 -30.6
LVL 0.10 -40.9
MSR 20.70 N/A
MSR -5.9 -21.4
MSR 38.70 15.6

(a) E:G ratios from ASTM D 198 Torsion use the E value from
ASTM D 198 Bending.

(b) Percent difference = (Experimental E:G -16.0:1.0)/]
6.0:1.0 x 100 percent.

(c) Percent difference-(Experimental E:G-ASTM D 198
E:G)/(ASTM D 198 E:G) x 100 percent.

Table 5.--Comparison of the percentage of shear deflection and shear
modulus COV values from experimental data.

 LVL MSR

 Shear Shear
 Shear modulus Shear modulus
Test method deflection COV deflection COV

ASTM D 198 Bending 16 (a) 36.3 11 (a) 56.0
ASTM D 198 Torsion 100 (b) 3.5 100 (b) 7.5
FPBT 52 (c) 14.2 55 (c) 24.1

(a) The range of values is given for the range of different lest
lengths used.

(b) All angular deflection was assumed to be considered as shear
deflection.

(c) This was the shear deflection present in the five-point loading.
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Title Annotation:Structural composite lumber
Author:Harrison, S. Kate; Hindman, Daniel P.
Publication:Forest Products Journal
Geographic Code:1USA
Date:Jul 1, 2007
Words:5348
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