United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

Research

Paper

FPL-RP-521

Effect of Various

Proportions of Juvenile

Wood on Laminated

Veneer Lumber

David E. Kretschmann

Russell C. Moody

Roy F. Pellerin

B. Alan Bendtsen

James M. Cahill

Robert H. McAlister

Donald W. Sharp
Abstract Contents

To satisfy the increased demand for forest products

while addressing environmental concerns, much of the

future timber supply will be from managed plantations

of rapidly grown trees. These trees will be harvested in

short-rotation cycles and will contain large quantities

of juvenile wood. This report discusses the influence

that Douglas-fir and Southern Pine juvenile wood has

on veneer grading and its implications on structural

performance of laminated veneer lumber (LVL). Veneer blocks cut from fast-grown Douglas-fir and Southern Pine lumber were examined and divided into three

zones based on age: mature, transition, and juvenile.

Veneer peeled from these zones was tracked through the

peeling, drying, and grading process. The LVL made

of various proportions of juvenile and mature veneer

was tested in flatwise bending, edgewise bending, and

tension. Results of this study suggest that two forms

of nondestructive grading techniques are capable of

placing juvenile material in a low-grade classification.

Also, during veneer preparation, the low strength of juvenile wood veneer in both species led to a significant

increase in breakage during handling when compared

to normal veneer losses. The LVL manufactured in this

study showed a predictable decrease in strength and

stiffness with increased juvenile wood content. The ratio of juvenile to mature material in the same nondestructive grade for Southern Pine and Douglas-fir was

approximately 0.8 for strength and stiffness. This study

demonstrates that an LVL-type product with structural integrity using significant quantities of juvenile

wood veneer is possible but will result in products with

design values lower than those of mature wood. The

amount of juvenile wood acceptable to manufacturers will depend on the economic consideration of each

manufacturer.

Keywords: Juvenile wood, laminated veneer lumber, Douglas-fir, Southern Pine, proportions, stiffness,

tension, bending

July 1993

Kretschmann, David E.; Moody, Russell C.; Pellerin, Roy

F.; Bendtsen, B. Alan; Cahill, James M.; McAlister, Robert

H.; Sharp, Donald W. 1993. Effect of various proportions

of juvenile wood on laminated veneer lumber. Res. Pap.

FPL-RP-521. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 31 p.

A limited number of free copies of this publication are

available to the public from the Forest Products Laboratory, One Gifford Pinchot Drive, Madison, WI 53705-

2398. Laboratory publications are sent to more than 1,000

libraries in the United States and elsewhere.

The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin.

Research highlights . . . . . . . . . . . . . . i

Terminology. . . . . . . . . . . . . . . . . . . ii

Introduction . . . . . . . . . . . . . . . . . . 1

Background . . . . . . . . . . . . . . . . . 1

Clear wood . . . . . . . . . . . . . . . . . 2

Solid-sawn lumber . . . . . . . . . . . . . . 2

Laminated-veneer lumber. . . . . . . . . . . 2

Experimental methods. . . . . . . . . . . . . 3

Material selection and preparation. . . . . . 3

Manufacture of LVL billets. . . . . . . . . . 5

Evaluation . . . . . . . . . . . . . . . 6

Economic analysis. . . . . . . . . . . . . . 7

Results and discussion . . . . . . . . . . . . . 7

Moisture content and specific gravity. . . . . 7

Strength and stiffness variability. . . . . . . 7

Low-grade core content. . . . . . . . . . . . . . 9

Strength and juvenile wood. . . . . . . . . . 9

Modulus of elasticity and juvenile wood . . . . 10

Similarities and differences. . . . . . . . . . 11

Mature and juvenile low-grade material. . . . 11

Flatwise and edgewise bending. . . . . . . . 12

Tensile properties and juvenile wood. . . . . 13

Size effect. . . . . . . . . . . . . . . . . 13

Remanufactured edgewise bending specimens. . 14

Failure codes and warp characteristics. . . . . 14

Value effect. . . . . . . . . . . . . . . . . 15

Conclusions . . . . . . . . . . . . . . . . . . 15

Future considerations. . . . . . . . . . . . . 16

Acknowledgments. . . . . . . . . . . . . . . . 16

References . . . . . . . . . . . . . . . . . . . 16

Appendix A-Specimen preparation . . . . . . . 18

Appendix B-Data summary tables . . . . . . . 19

Appendix C-Cumulative frequency distributions . 23

Appendix D-Failure code summary. . . . . . 27

Appendix E-Economic analysis. . . . . . . . 30

Page
Research Highlights l

To satisfy the increased demand for forest products

while addressing environmental concerns, much of the

future timber supply will be from young-growth trees

from managed plantations. These trees will be harvested in short-rotation cycles and will contain large

quantities of juvenile wood. This report discusses the

influence of Douglas-fir and Southern Pine juvenile

wood on veneer grading and its implications on structural performance of laminated veneer lumber (LVL).

The objectives of this study were to determine the influence of varying the proportion of juvenile wood on

mechanical properties, examine the effectiveness of nondestructively sorting juvenile veneer, compare the warp

characteristics of proposed LVL lamination schemes,

and conduct a preliminary economic analysis of increasing juvenile wood content in LVL.

The Douglas-fir veneer source represents a lower bound

on the quality of the veneer sources that are anticipated in the future, and the Southern Pine veneer material represents the typical quality expected in fastgrown Southern Pine veneer supplies. Veneer blocks cut

from fast-growing Douglas-fir and Southern Pine were

examined and divided based on age into three zones:

mature, transition, and juvenile. Veneer peeled from

these zones was tracked through the peeling, drying,

and grading process. The LVL made of various proportions of juvenile and mature veneer was manufactured

and tested in 2 by 2 flatwise bending, 2 by 2 edgewise

bending, 2 by 4 tension, and 2 by 8 edgewise bending.

The results of this study indicate the following:

l It is possible to manufacture an LVL type product with structural integrity using significant

quantities of juvenile wood veneer, but design

values would be lower than those currently in

use.

LVL stiffness properties for Douglas-fir and Southern

Pine reacted similarly to the inclusion of juvenile

material. However, strength results for Douglas-fir

were much more affected by the inclusion of juvenile

material than was Southern Pine.

A significant difference exists between material manufactured with mature or juvenile material having

the same nondestructive grade.

The two techniques of nondestructive grading used

in this study are capable of indicating the low

quality of veneer sheets and placing them into low

grades. However, these techniques are unable to differentiate between low-grade mature and juvenile

material.

No difference in warping characteristics existed between the different layups investigated.

l The amount of juvenile wood acceptable to manufacturers will be heavily influenced by the manufacturer’s production costs and performance requirements. Compared to mature wood, the falldown rate

of veneer containing juvenile wood nearly doubled.

As a result of this study, areas for improvement in the

manufacturing process of LVL are suggested. An improved method is needed to sort the juvenile wood material prior to processing. Also, improved methods to

dry and handle juvenile wood veneer are necessary to

reduce the large falldown expected. If the high amount

of resin, pitch, and tar found in this study are typical

of Southern Pine juvenile wood, improved manufacturing techniques to handle anticipated difficulties will

have to be developed. Finally, accurate estimates are

needed of how much young-growth material will enter

the market place.
Terminology

Billet

Block

Blow

Butt Block

CFD

Falldown

Fb

Log-run

LVL

M C

MOE

ii

Large sheet of material either 2 or 4 ft

(0.6 or 1.22 m) wide composed of a number

of parallel laminated plies of veneer sheets

1mE Billet Billets made entirely of 1mE

tight band veneer

2m Billet Billets made entirely of 2m

veneer

2j Billet Billets made entirely of 2j

veneer

D Billet Billets with exterior plies

of 1mE tight band mature

veneer and various proportions of low-grade core veneer

(2j or 2m)

D25j D Billets with 25% low-grade

juvenile wood core veneer

D50j D Billets with 50% low-grade

juvenile wood core veneer

D50m D Billets with 50% low-grade

mature wood core veneer

D57j D Billets with 57% low-grade

juvenile wood core veneer

D57m D Billets with 57% low-grade

mature wood core veneer

D75j D Billets with 75% low-grade

juvenile wood core veneer

Short subsection of a log that is conditioned and placed in a lathe for peeling

into veneer

Heat delamination

Block from the bottom or butt of the tree

Cumulative frequency distribution

Veneer that does not make it through the

manufacturing process

Allowable bending strength

Logs as they arrive at the mill yard

Laminated veneer lumber, material made

by parallel lamination of veneers into thicknesses common to solid sawn lumber

Moisture content

Modulus of elasticity

MOR

NDE

R

Top Block

UPT

UTS

VGS

2 by 2

2 by 4

2 by 8

1m

2 m

1mE

1t

2t

1j

2j

Modulus of rupture

Nondestructive evaluation

Remanufactured specimens made from

1mE exterior and 2j core veneer

R25j Remanufactured specimens with

25% 2j core veneer

R50j Remanufactured specimens with

50% 2j core veneer

R75j Remanufactured specimens with

75% 2j core veneer

Any block above the butt block

Ultrasonic propagation time

Ultimate tensile stress

Veneer grading system

Test specimens having a cross section of 1.5

by 1.5 in. (38 by 38 mm); also referred to

as small bending specimens

Test specimens having a cross section of 1.5

by 3.5 in. (38 by 89 mm); also referred to

as tension specimens

Test specimens having a cross section of 1.5

by 7.5 in. (38 by 191 mm); also referred to

as large bending specimens

Mature veneer sheets that are greater than

the preselected grading cut-off

Mature veneer sheets that are less than the

preselected grading cut-off

Material selected from the subset of 1 m

veneer that is estimated to have a stiffness

of 2.0 x 106 lb/in2 ± 0.2 x 106 lb/in2; also

referred to as tight band material

Transition veneer sheets that are greater

than the preselected grading cut off

Transition veneer sheets that are smaller

than the preselected grading cut off

Juvenile veneer sheets that are greater

than the preselected grading cut off

Juvenile veneer sheets that are less than

the preselected grading cut off
Effect of Various Proportions of Juvenile

Wood on Laminated Veneer Lumber

David E. Kretschmann, Research General Engineer

Russell C. Moody, Supervisory Research General Engineer

Forest Products Laboratory, Madison, Wisconsin

Roy F. Pellerin, Professor

Washington State University, Pullman, Washington

B. Alan Bendtsen, Supervisory Forest Products

Technologist (retired)

Forest Products Laboratory, Madison, Wisconsin

James M. Cahill, Research Forester

USDA Forest Service, Pacific Northwest Station, Portland, Oregon

Robert H. McAlister, Research Forester

USDA Forest Service, Southeastern Station, Athens, Georgia

Donald W. Sharp, System Performance Engineer

Trus Joist/MacMillan Corp., Boise, Idaho

Introduction

Laminated veneer lumber (LVL) is a high-performance

product that was developed in response to a need for

increased strength and stiffness, good dimensional stability, and low variability in highly engineered structural components (Forest Products Laboratory 1987).

To ensure the high-performance characteristics of LVL,

some manufacturers use nondestructive evaluation

(NDE) grading techniques to sort low-stiffness veneer

from LVL stock. As the forest products industry moves

toward a rapidly grown, young wood resource, it is suspected that the amount of veneer rejected by NDE

grading techniques will increase because of the predominance of juvenile wood. A thorough understanding of

the properties and problems associated with manufacturing juvenile wood is needed, so that processing procedures can be modified to utilize this resource without sacrificing high-performance characteristics. The

objectives of this study were the following:

a. Determine the influence of varying the proportion

of juvenile wood on the mechanical properties of an

LVL product.

b. Examine the effectiveness of nondestructively sorting

juvenile veneer.

c. Compare the warp characteristics of proposed LVL

lamination schemes.

d. Conduct a preliminary analysis on the cost of increasing juvenile wood in LVL products compared

to the cost of current LVL and solid-sawn lumber

products.

Background

The low strength and stiffness values of juvenile wood

are a concern in North America and overseas. Summaries of the initial work on the properties of juvenile wood are found in Bendtsen (1978, 1986). Since

Bendtsen’s research, a significant amount of literature

has been added on the effect of juvenile wood on clear

wood and dimension lumber. However, the same type

of research on LVL has been limited.
Clear Wood

Work by Boone and Chudnoff (1972) and Bower and

others (1976) on plantation Caribbean pine drew attention to the properties of plantation material. Both

works reported that clear wood plantation material

had less than 50% of expected specific gravity, bending strength, and stiffness for virgin timber of the same

species. At the same time, research by Pearson and

Gilmore (1971) on clear wood of loblolly pine clearly

demonstrated that the problem was juvenile wood, not

plantation wood. Their research found juvenile wood to

have substantially lower values of mechanical properties

than did mature wood. This accounts for the subordinate properties of plantation wood when compared to

that of old-growth timber.

Intricate work by Bendtsen and Senft (1986) demonstrated that properties for loblolly pine and eastern cottonwood are important to solid wood utilization. These woods are subpar in the first-formed

annual ring, improve dramatically each year in the

early juvenile wood zone, and improve more gradually during the latter years. Early juvenile wood

(juvenile wood closest to the pith) is distinctly of

poorer quality than later juvenile wood. Properties that influence mechanical behavior include

fibril angle, cell length, and specific gravity-the

latter a composite of the percentage of late wood, cell

wall thickness, and lumen diameter. Bendtsen and

Senft (1986) results suggest that the ratios of juvenile wood to mature wood for strength and stiffness

range from 0.59 to 0.78 and 0.47 to 0.62, respectively.

The excessively high micro-fibril angle in juvenile wood

causes excessive longitudinal shrinkage that may be

more than 10 times that of mature wood. Compression

wood and spiral grain, both more prevalent in juvenile

wood than in mature wood, also contribute to excessive

longitudinal shrinkage.

Factors that affect transition to mature wood were also

investigated. For Southern Pine, the length of juvenile

growth in years was shown to be dependent on geographic location (Clark and Saucier 1989). The length

of juvenility was also shown to differ from species to

species. For example, Southern Pine can have a range

of juvenility from 6 to 14 years (Bendtsen and Senft

1986, Clark and Saucier 1989). Red pine is reported

to have a juvenile wood transition from 14 to 17 years

(Smith and others 1991). Douglas-fir is considered to

have a gradual transition that ends after 18 to 23 years

(Di Lucca 1989, Megraw 1985).

Solid-Sawn Lumber

The potential problem of low mechanical property values in juvenile wood structural lumber was perhaps

2

first observed by Koch (1966) while involved in research

to develop straight studs from Southern Pine veneer

cores. He found that most of these studs had lower

bending strength and stiffness than was expected for

Southern Pine studs in general. Additional evidence

of property reduction of lumber as a result of juvenile

wood was suggested by Moody (1970) when evaluating finger joints in Southern Pine lumber, No. 1 or

Better. Moody noted that the strength and stiffness of

control specimens with pith-associated materials were

respectively 30% and 10% less than that of material

not containing pith.

Since these first indications of juvenile wood effects,

much international work has been done on how juvenile

wood properties compare to mature wood properties for

full-size lumber. In the United States, several studies

evaluated the influence of juvenile wood on the mechanical properties of Douglas-fir and Southern Pine dimension lumber (Bendtsen and others 1988, Biblis 1990,

Fahey and others 1991, Kretschmann and Bendtsen

1992, MacPeak and others 1990, Pearson 1984). In New

Zealand, work by Bier and Collins (1984) and Tsehaye

and others (1991) looked at Radiata pine. In Canada,

Douglas-fir was studied by Barrett and Kellogg (1989).

These studies indicate that lumber cut from the juvenile wood zone of logs has the potential to be significantly less in strength and stiffness than does lumber

from the mature wood zone; the magnitude of reductions varies by species. For example, ratios of mature

to juvenile wood material for Douglas-fir modulus of

rupture (MOR), ultimate tensile stress (UTS), and

modulus of elasticity (MOE) range from 0.62 to 0.97,

0.62 to 0.97, and 0.45 to 0.75, respectively, and ratios

for Southern Pine MOR, UTS, and MOE range from

0.54 to 0.74, 0.51 to 0.77, and 0.45 to 0.59, respectively.

The magnitude of reductions in strength or stiffness

also seems to vary by and within species. For example,

juvenility seems to have a greater influence on Southern Pine than on Douglas-fir. For Douglas-fir, the MOE

ratio of all-mature to all-juvenile material is less influenced by juvenile wood than is MOR. For Southern

Pine, the magnitude of the reduction in the ratio of juvenile to mature material is similar for strength and

stiffness (Bendtsen and others 1988, Kretschmann and

Bendtsen 1992).

Laminated-Veneer Lumber

In the literature by Biblis and Mercado (1991), Braun

and Moody (1977), Jung (1982), Moody (1972), Stump

and others (1981), and Youngquist and others (1984),

no effort was made to identify the differences between

juvenile and mature material. However, one study investigated the difference between juvenile and mature

bending and compression strength of LVL made from
larch (Jo and others 1981). This study indicated that

specimens of 100% juvenile wood had a ratio of juvenile to mature wood compression strength of 0.9 and

bending strength of 0.7.

In summary, intricate studies of clear wood have produced a thorough understanding of the physical property changes that occur as a result of juvenile wood.

Several studies completed on solid-sawn lumber have

provided a good understanding of how juvenile wood

affects the mechanical properties of solid-sawn lumber.

However, the information available on the effect of juvenile wood in reconstituted wood products is minimal.

Experimental Methods

This study investigated the effects of mature and juvenile wood on LVL made of Douglas-fir and a mixture of

slash and loblolly pine. The study involved the cooperation of several institutions for study plan development,

material selection and preparation, manufacture of LVL

billets, and evaluation.

Material Selection and Preparation

Log Procurement and Identification

Through the cooperation of the USDA Forest Service

and the forest products industry, a careful selection

process was used to ensure that the logs to be peeled

were from rapidly grown trees. The logs were obtained

from the inventory of cooperating veneer mills. As previously described, the transition from juvenile wood to

mature wood can vary from geographic location and

species. We decided that the ages that would best represent the beginning and end of the transition to mature material would be 12 and 18 years for Douglas-fir

and 8 and 12 years for Southern Pine (Fig. 1).

The Douglas-fir sample blocks were selected from logs

cut from one 53-year-old stand located in the coastal

mountains of Oregon with a site index (50 year) of 134

(King 1966). Stocking throughout the stand history

was light. Trees had characteristics often associated

with open-grown trees-large persistent limbs varying

in size from 1 to 2-1/2 in. diameter and wide, coarse

annual growth rings. (See Table 1 for metric conversion.) Logs were selected log-run until we had a sufficient number to generate the volume of juvenile wood

required to make the LVL billets. Diameter measurements were taken on both ends of 338 blocks. Average diameters at 12 and 18 years were 8.4 and 11.8 in.,

respectively. The growth rate of this material averaged 2.9 rings per inch. We emphasize that logs were

sampled from one, relatively fast-grown stand and do

not necessarily represent the average quality of the

Douglas-fir young-growth resource in the Pacific

Figure 1–Zones of material tracked in veneer.

Table 1—SI conversion factors

English unit Conversion factor SI unit

foot (ft)

inch (in.)

pound per square

inch (lb/in2)

(stress)

pound-force (lbf)

degree Fahrenheit

(°F)

0.3048 meter (m)

25.4 millimeter

(mm)

6,895 Pascal (Pa)

4.448 newton (N)

Celsius (C)

Northwest. In general, we felt that the Douglas-fir logs

used would best be characterized as low-quality material and expected to represent a lower bound of quality. The blocks were conditioned using typical industry

schedules.

The Southern Pine material consisted of 416 blocks of

a mixture of slash and loblolly pine selected from yard

inventory of a plywood plant in Cedar Springs, Georgia. The material was from 20- to 30-year-old trees.

Logs were selected at the debarker from log-run and cut

into blocks. We selected enough material to make one

charge of the plant’s conditioning facilities. Fast-grown,

cylindrical, even-growth-rate logs were selected. The

growth rate of this material averaged 2.8 rings per inch.

The mixture of blocks was approximately two top for

each butt block. The blocks selected were conditioned

in a steam vat using a typical industry schedule.

Veneer Peeling, Drying, and Handling

The veneer sheets were divided into three categories

based on the annual growth rings: an outer mature

zone, a transition zone, and a juvenile core (Fig. 1).

The positions at which the bolts had 8 and 12 annual

rings in the south and 12 and 18 annual rings in the

3
west were used as cut-off points to separate the veneer

into the mentioned categories.

The Douglas-fir material was processed at a veneer

mill in Independence, Oregon. Mill equipment allowed each veneer ribbon to be painted to differentiate between mature, transition, and juvenile core

as each block was being peeled. This was accomplished by using the rings marked at the end of each

bolt. The mature zone, transition zone, and juvenile

core categories were marked using portable equipment on the top surface of the veneer with dye as it

was peeled off the bolt. The dye markings were triggered by a person located near the veneer lathe who

was in a position to observe the end of the veneer

bolt as it was peeled. When the knife passed through

the ring marked on the bolt, the appropriate dye was

triggered. Of the 338 blocks selected, we peeled 182

8-ft blocks, from which approximately 1,440 sheets of

juvenile, 1,100 sheets of transition, and 1,800 sheets of

mature 1/10-in. veneer were produced. The 182 blocks

were peeled to the smallest possible core (approximately 5 in.) to maximize the juvenile wood yield and

include as much early juvenile wood as possible. Note

that the lathe speed had to be reduced by one-third to

peel the Douglas-fir juvenile wood to a veneer thickness

of 1/10 in.

After peeling, the veneer was shipped to an LVL plant

in Junction City, Oregon, for drying. The Douglas-fir

juvenile wood appeared to dry quicker than did the mature veneer. To compensate for this, the veneer dryers

were run at a low-temperature, high-speed redry schedule while processing the juvenile veneer.

The Southern Pine veneer was peeled in a normal process to 1/8 in., with no reported adjustments for the juvenile wood. The 416 blocks were peeled to the smallest possible core (3.5 in.) to maximize the juvenile

wood yield and include as much early juvenile wood

as possible. Prior to conditioning and peeling the veneer, diameters at 8 years were measured on 50 bolts in

the yard to obtain an estimated average juvenile wood

core diameter of 6 in. The average outside diameter for

the bolts was 12 in.

Because of available equipment at the Southern Pine

mill, the marking of the veneer was initiated when the

bolt diameter reached 6 in. A single-dye spraying unit

was located one and one-half veneer sheets from the

lathe knife. When marked, the veneer traveled through

an in-line dryer. Drying was completed using a typical

drying schedule with no adjustments for juvenile wood.

After emerging from the dryer, the veneer ribbon came

past the clipper and was cut into sheets. Each sheet

was numbered sequentially using dye as it emerged

from the clipper. The material without dye was consid4

ered to be mature veneer. The first two veneer sheets

having a dye mark were considered transition material,

and the remaining sheets were judged to be juvenile

core material. The veneer collected was shipped dry to

an LVL plant in Natchitoches, Louisiana.

Grading of Mature and Juvenile Veneer

Veneer sheets were sorted and graded into two categories (high and low) using nondestructive mechanical

techniques. The grade distribution for the various zones

of veneer from this particular source of material was

not known prior to the grading process. An exploratory

grading run of the veneer sheets from the veneer mill

for each area established an estimated distribution

of the NDE parameter for juvenile and mature wood

sheets. To investigate the effectiveness of current grading techniques on juvenile wood material, we set up an

NDE grading parameter cut-off point that would allow

low-grade mature wood in the overlapping region between the juvenile and mature wood distributions. The

remaining veneer sheets from the veneer mill source

were graded based on this cut-off point.

The grading process resulted in seven grade classifications of the veneer sheets: 1m, 1mE, 2m, 1t, 2t, 1j,

and 2j (Fig. 2). The subset of grade 1m veneer, designated grade 1mE, came from a tight band with an estimated MOE of 2.0 × 106

 lb/in2 ±5%. The tight band

of MOE was meant to eliminate the high and low tails

of mature material from the mature zone distribution.

Low-strength core material and some high-strength mature zone material could be dominated by the highstrength material, thus making the effect of the juvenile wood material unclear. Therefore, the value of

2.0 × 106 lb/in2 was selected because it represented a common stiffness that is produced by LVL

manufacturers.

Grading Effectiveness

The Douglas-fir veneer was graded on an ultrasonic

veneer grader. After running a test batch of trial veneer, an ultrasonic propagation time (UPT) of 550 μs

was selected as the grading cut-off point. The juvenile

material consistently had a longer UPT (implying low

grade) than did the mature material (Fig. 3). We also

observed that juvenile veneer produced four times as

many grading signal failures than did the mature veneer. These observations suggest that the threshold

levels for the grading signals should be further investigated as a means of more effectively grading juvenile

material. A random sample indicated that the relative density of Douglas-fir juvenile veneer was approximately 20% less than that of normal Douglas-fir veneer.

The Southern Pine veneer was graded by a proprietary

veneer grading system (VGS) that incorporated UPT
Figure 2–Grade designations for nondestructive

evaluation techniques to sort veneer.

Figure 3–Grading results for Douglas-fir veneer

using an ultrasonic pulse technique.

Figure 4–Grading results for Southern Pine veneer using the VGS.

and a density measurement into a grading model. After

running the trial grading run of the juvenile and mature veneer, the cut-off point was selected to be a VGS

grade of 1.8 × 106 lb/in2. Again, a clear difference in

the grading machine distributions was noted between

the grading results of the juvenile veneer and the mature veneer (Fig. 4) with the transitional veneer falling

between. The VGS predicted an average MOE of about

1.67, 1.85, and 1.93 × 106 lb/in2 for the juvenile, transition, and mature veneer, respectively. The juvenile

veneer was 16% less than the normal 2.0 × 106 lb/in2

for the plant. The relative density of Southern Pine

was determined by the VGS to be about 5% less than

that of a typical mill supply of veneer.

The nondestructive techniques applied in the western

and the southern United States have the capability of

placing juvenile material in a low grade with low stiffness values. The VGS machine, using both UPT and

density as predictors, was successful in assigning grades

to the processed veneer. The ultrasonic veneer grading

machine, having a high frequency of signal failures on

juvenile material, also suggests that this machine may

be used as an indicator of low-quality juvenile material.

The juvenile wood veneer in both species had a significant increase in breakage during handling compared

to that of normal mill veneer. In fact, the drying and

grading falldown was nearly double that of the mill’s

normal veneer run.

Manufacture of LVL Billets

Manufacturing for both species was in accordance with

normal procedures of the LVL manufacturer for the

1.5-m-thick billets produced. A continuous hot press

produced the LVL from multiple plies using 8-ft-long

veneer sheets with 2-in. overlapping veneer joints and

an exterior-type (phenol formaldehyde) adhesive spread

on one side. The glue was applied at a spread rate of

40 to 45 lb/ft2 on Southern Pine and 30 to 35 lb/ft2 on

Douglas-fir.

Layup

Three grades of veneer sheets were used to manufacture the billets: tight band 1mE, low-grade mature 2m,

and low-grade juvenile 2j. Four types of billets were

manufactured from the three grades (1mE, 2m, 2j, and

D). The first type of billets (1mE) was made of 1mE

mature wood veneer from only the peeled veneer mill

source that had been sorted into a tight range of MOE

(2.0 × 106 lb/in2 ± 5%). The second type of billets

(2m) was made from grade 2m mature zone veneer.

The third type of billets (2j) was made from 2j grade

juvenile core veneer. The fourth type of billets (D) was

5
made from a mixture of 1mE grade veneer for external

plies and juvenile 2j grade or 2m mature grade veneer

as core (Figs. 5a,b). When the mature wood from the

veneer mill source was exhausted, veneer that had been

sorted into the same tight range of MOE from plant

stock was used to fill in the manufacture of the required

number of billets. The plant stock used to fill was at

most 30% of the 1mE material used.

Because of material and equipment restrictions, the

method of LVL manufacture differs in the western and

southern United States. The manufacturing techniques

require two billet lay-up schemes and billets sizes.

Billets of Douglas-fir were defined to be 2 ft wide, 12 ft

long, and 1.5 in. thick. The billets were manufactured

from 16 2-ft-wide by 8-ft-long by 1/10-in.-thick veneers

oriented parallel to the lengths of the billets in a continuous hot press (Fig. 5a). A total of 118 12-ft billets

were manufactured: 19 each of class 1mE and class 2j

billets, 16 of class 2m, and 16 each of four types of class

D (D25j, D50j, D50m, or D75j, i.e., 25%, 50%, and 75%

low-grade core).

Billets of Southern Pine were defined to be 4 ft wide,

12 ft long, and 1.5 in. thick. The billets were manufactured from 14 1/8-in. veneers oriented parallel

to the lengths of the billets in a continuous hot press

(Fig. 5b). A total of 32 billets were manufactured in

the South: 6 class 1mE and class 2m, 8 class 2j, and 6

each of two types of class D (D57j and D57m, i.e., 57%

low-grade core).

Concerns

No difficulty was encountered in the manufacturing of

the Douglas-fir billets. The material handled and behaved similarly to typical Douglas-fir veneer supplies.

However, a significant number of the Southern Pine billets containing juvenile veneer were damaged by heat

delaminations or blows. The high frequency of blows

was attributed to primarily a high pitch content and

elevated moisture content in the juvenile wood veneer.

Posey and Robinson (1969) observed an increase in extractive content near the pith, depending on the age

of the tree. The result was that a considerable number

of potential specimens had to be discarded because of

blows to the center portion of the billets.

Specimen Preparation

Appendix A gives the scheme for the specimen preparation and remanufacture. The 12-ft billets (118 Douglasfir and 32 Southern Pine) were ripped into 12-ft-long

strips of specified widths at the LVL plants. The strips

of material were shipped to the testing laboratory at

Washington State University.

6

Figure 5–Layups for LVL billets produced with

(a) Douglas-fir and (b) Southern Pine.

Prior to testing, all strips from the manufacturing

plants were conditioned to equilibrium in a climate controlled room under 65% relative humidity and 75°F

(approximately 12% equilibrium moisture content).

After conditioning, the strips were cut to produce

matched 1.5- by 1.5- by 30-in. (2 by 2) edgewise and

flatwise small bending specimens, 1.5- by 3.5- by 96-in.

(2 by 4) tension specimens, and 1.5- by 7.4- by 144-in.

(2 by 8) edgewise large bending specimens from each

billet. This was done according to a cutting pattern

that would maximize the variability between specimens

that were cut from the same billet while using all the

material produced.

The remaining specimens were 2 by 8 bending specimens made of one 2j core strip glued between two mature 1mE strips, referred to as remanufactured specimens (R) (Fig. 6). The Douglas-fir strips designated

for remanufacture were glued together to form one of

the three types of 2 by 8 bending specimens: R25j,

R50j, or R75j (25%, 50%, and 75% 2j core). The core

and exterior veneer sheets were oriented vertically. The

Southern Pine specimens had a considerable amount of

material that had to be discarded as a result of delamination blows in the center of the billets. This resulted

in an inadequate number of specimens for the initial

test matrix. Therefore, we used the strips cut for remanufacture to supplement the remaining test material.

Evaluation

Test results were to be obtained for moisture content,

specific gravity, tensile and bending strength, and stiffness for the various specimens produced from the four

types of billets. The following tests were conducted in

accordance with ASTM D 2395 and D 4761 (1991):
Figure 6–Remanufactured 2 by 8 specimen

layup, veneer sheets running vertical.

a.

b.

C.

d.

Edgewise and flatwise flexure of 2 by 2 LVL with

third-point loading over a span to depth ratio of

17:1. For all bending specimens, the information

was measured, recorded, or calculated for billet type,

cross-section dimension, modulus of rupture (MOR),

modulus of elasticity (MOE), moisture content (MC)

at time of test, and failure code.

Tension of 2 by 4 LVL with an approximate span of

48 in. For tension tests, information was measured,

recorded, or calculated for billet type, cross-section

dimension, ultimate tensile stress (UTS), MOE, MC

at time of test, and failure mode.

Edgewise flexure of 2 by 8 LVL with third-point

loading over a span to depth ratio of 17:1. The same

information gathered for the small bending tests was

gathered for the large bending tests. Prior to testing, information was also gathered on warp (twist,

bowing, or crook).

Specific gravity for each 1.5-in. strip of the billet

was obtained from the 1.5- by 3.5- by 18-in. sections. Specific gravity was determined for ovendry

weight and ovendry volume.

Economic Analysis

A baseline of typical strength and stiffness material was

manufactured and labeled 1mE. Two categories were

established for analysis: veneer costs and other costs.

Other economic factors included forest taxes, inventory,

electricity, and labor. The baseline strength and stiffness data and production costs were used to estimate

the relative value of juvenile veneer to the current veneer supply. The remaining test results for the various

low-grade core combinations were used to estimate the

amount of additional material that would be needed to

produce a product capable of the same load-carrying

or deflection capacity. The deflection and load-carrying

capacity for each cross-section was estimated by using

simple beam theory. This analysis allows for a preliminary look at the value that should be associated with

juvenile veneer.

Results and Discussion

The mean test results for moisture content, specific

gravity, strength, and stiffness for the various combinations of the three grades of veneer are listed in

Tables 2 and 3. A detailed summary of the test results

is provided in Appendix B. The cumulative frequency

distribution (CFD) values of strength and stiffness are

given in Appendix C. In the following discussion, where

differences are reported, the transition material was

expected to fall somewhere between the extremes of

juvenile and mature wood.

Moisture Content and Specific Gravity

For both Douglas-fir and Southern Pine, specimens

were very close to the target 12% MC (Tables 2, 3).

The levels ranged from 10.1% to 14.6% MC with the

exception of the 2 by 4 tension specimens containing

50% juvenile wood. Equipment failure caused 10 specimens to have an unexpected and undetected exposure

to moisture, resulting in moisture levels greater than

15% for those specimens. The results are reported with

and without the 10 specimens.

The density difference between the juvenile veneer and

typical veneer supply is reflected in the specific gravity

results for both Douglas-fir and Southern Pine. As lowgrade core material increased, specific gravity values decreased. The density of the low-grade mature and the

low-grade juvenile materials also showed a detectable

difference. The Southern Pine material appeared to

have a much closer match between low-grade mature

and low-grade juvenile veneer density levels than did

the Douglas-fir. The ratio of the low-grade juvenile

to the low-grade mature materials for Douglas-fir was

0.87, and the ratio for Southern Pine was 0.94.

Strength and Stiffness Variability

The coefficient of variation (COV) averaged 13.5%

(range 6.2% to 26.5%) for strength and 10% (range

3.6% to 22.1%) for stiffness. As the percentage of lowgrade core material increased, the variability increased

7
Table 2—Douglas-fir test resultsa

Test

Moisture content Specific gravity Strength Modulus of elasticity

Coefficient Coefficient Coefficient Coefficient

of of of Mean of

Identi- Sample Mean variation variation Mean variation (×106

variation

fication sizea

(%) (%) Mean (%) (lb/in2

)

(%) lb/in2

)

(%)

2 by 2

a

1mE 60 12.1 2.7 0.52 5.4 9,850 7.6 1.86 11.2

edgewise D25j 64 11.9 4.0 0.52 5.2 9,290 9.4 1.78 9.5

bending D50j 64 12.3 2.9 0.48 5.2 7,170 11.7 1.56 6.7

D50m 64 11.8 2.9 0.51 5.4 8,340 9.9 1.74 6.1

D75j 64 12.5 2.0 0.46 5.2 6,690 12.6 1.43 7.9

2j 60 11.9 2.2 0.45 6.2 5,500 16.0 1.30 10.1

2m 64 11.9 3.6 0.50 5.3 6,450 22.6 1.59 11.2

2 by 2

a

1mE 60 12.1 2.7 0.52 5.4 8,930 11.7 1.98 12.7

flatwise D25j 64 11.9 4.0 0.52 5.2 9,270 13.2 1.89 10.0

bending D50j 64 12.3 2.9 0.48 5.2 8,190 13.6 1.88 8.5

D50m 64 11.8 2.9 0.51 5.4 8,700 11.5 1.79 7.8

D75j 64 12.5 2.0 0.46 5.2 7,540 11.3 1.61 8.1

2j 60 11.9 2.2 0.45 6.2 4,900 21.5 1.30 14.4

2m 64 11.9 3.6 0.50 5.3 5,720 24.3 1.60 15.6

2 by 4 1mE 60 11.9 3.5 0.52 5.4 7,100 11.5 1.87 6.9

tension D25j 64 11.6 3.8 0.52 5.2 6,540 12.3 1.76 5.8

D50j 64 13.0 12.5 0.48 5.2 5,270 11.6 1.58 5.0

D50j 54b

12.4 7.0 0.48 5.2 5,170 11.5 1.59 5.0

D50m 64 11.9 3.8 0.51 5.4 5,780 9.9 1.68 4.8

D75j 64 12.1 2.9 0.46 5.2 4,320 10.7 1.44 6.5

2j 60 12.2 3.0 0.45 6.2 3,020 11.8 1.24 6.1

2m 64 11.5 3.0 0.50 5.3 3,920 10.6 1.57 5.5

2 by 8 1mE 15 11.4 2.2 0.52 5.4 8,490 6.2 1.90 4.3

edgewise D25j 16 11.3 4.6 0.52 5.2 8,030 12.7 1.84 7.3

bending D50j 16 11.6 3.1 0.48 5.2 6,430 14.1 1.67 5.7

D50m 16 11.0 3.0 0.51 5.4 7,070 8.9 1.72 5.1

D75j 16 12.2 3.5 0.46 5.2 5,360 14.5 1.48 7.2

2j 15 11.4 2.9 0.45 6.2 3,610 9.4 1.17 8.7

2m 16 11.5 4.5 0.50 5.3 5,260 12.1 1.58 4.9

2 by 8 R25j 8 11.5 1.9 0.52 5.2 8,070 8.2 2.00 3.6

remanu- R50j 8 11.7 5.4 0.48 5.2 7,940 11.2 1.95 4.6

facture R75j 8 11.3 2.5 0.46 5.2 6,760 8.7 1.73 6.1

a

In some instances for the 2 by 2 specimen, sample size for MOE was smaller by one or two

specimens because of difficulties with measuring deflection.

b

2 by 4 results with specimens having greater than 15% moisture content were not included.

8
Table 3—Southern Pine test resultsa

Test

Moisture content Specific gravity Strength Modulus of elasticity

Coefficient Coefficient Coefficient Coefficient

of of of Mean of

Identi- Sample Mean variation variation Sample Mean variation (×106

variation

fication sizea

(%) (%) Mean (%) size (lb/in 2

)

(%) lb/in2

)

(%)

2 by 2

a

1mE 51 12.0 3.3 0.63 3.2 64 10,190 13.4 1.98 13.6

edgewise D57j 31 11.9 3.7 0.60 5.3 46 8,120 19.3 1.57 14.8

bending D57m 48 11.7 3.6 0.62 4.9 58 9,220 14.1 1.73 14.2

2j 36 11.7 3.6 0.59 6.2 54 7,530 16.9 1.34 14.2

2m 50 11.9 3.1 0.59 4.9 50 9,210 12.5 1.74 14.4

2 by 2

a

1mE 51 12.0 3.3 0.63 3.2 64 9,650 14.6 1.89 14.5

flatwise D57j 31 11.9 3.7 0.60 5.3 46 7,850 26.5 1.49 22.1

bending D57m 48 11.7 3.6 0.62 4.9 58 9,020 17.4 1.79 12.2

2j 36 11.7 3.6 0.59 6.2 54 6,940 25.2 1.27 17.6

2m 50 11.9 3.1 0.59 4.9 49 8,580 20.0 1.70 16.8

2 by 4

tension

1mE 50 11.8 5.7 0.63 3.2 50 7,430 16.8 1.97 9.6

D57j 23 11.9 5.6 0.60 5.3 23 6,440 15.0 1.69 11.0

D57m 54 11.8 6.2 0.62 4.9 54 6,910 15.1 1.76 7.5

2j 35 11.6 6.8 0.59 6.2 35 5,210 14.0 1.39 11.8

2m 45 11.8 4.6 0.59 4.9 45 6,400 17.3 1.67 13.1

2 by 8 1mE 8 11.9 3.6 0.63 3.2

edgewise D57m 8 11.9 2.9 0.62 4.9

bending 2j 5 13.1 10.8 0.59 6.2

2m 9 11.9 1.0 0.59 4.9

8 9,060 5.9 1.73 5.8

8 7,810 12.4 1.53 11.6

5 6,660 6.4 1.26 4.0

9 7,750 13.3 1.72 7.9

a

Sample size for moisture content was less than sample size for strength and MOE because of

introduction of additional samples from remanufactured specimens.

(Tables 2, 3). In most cases, the stiffness results were lated using an approach based on the DELTA method

also less variable than were the strength results. The (a Taylor series approximation, Mood and others 1976)

edgewise bending results were less variable than were and a normal approximation. The effects of increasthe flatwise bending results; the large bending results ing proportions of low-grade material on the normalwere less variable than were the small bending results; ized mean values of strength and stiffness and the 90%

the Douglas-fir results were less variable than were the confidence intervals for all test results are illustrated

Southern Pine results. Variability within billets was with respective theoretical predictions in Figures 7 to

also examined, and little difference was detected for 11. For the edgewise bending and tension specimens, a

a given billet type in Douglas-fir. However, a notice- linear rule of mixtures approach was used for the theoable difference did exist between material at the center retical approximations. For the flatwise bending and reof the billet and the edge material in Southern Pine, manufactured 2 by 8 bending specimens, a transformed

with the edge being slightly stronger and stiffer than section approximation based on an apparent moment

the center. This was partially caused by manufacturing of inertia resulted in a cubic equation as the theoretical

difficulties encountered with the Southern Pine veneer. basis.

Low-Grade Core Content Strength and Juvenile Wood

To investigate the effect of increasing low-grade core Douglas-fir normalized test results and confidence incontent, the mean values in Tables 2 and 3 were nor- tervals are shown in Figure 7. In all cases, the mature

malized by taking the mean of each test result and di- wood strength test data closely matched the theoretividing it by the tight band all-mature-test mean value. cally predicted curve. The flatwise juvenile wood test

The 90% confidence interval for the ratios was calcu- results also closely followed the theoretically predicted

9
Figure 7–Normalized mean values for Douglas-fir 2 by 2 edgewise and flatwise bending, 2 by 8

edgewise bending, and 2 by 4 tension strength results compared to percentage of low-grade core

content. Solid and dashed lines represent theoretically predicted results for mature and juvenile

core material, respectively

cubic curve. However, the juvenile wood results for all

test modes indicated that the inclusion of 25% lowgrade juvenile material had little effect on the normalized strength. The 25% low-grade juvenile material was

within the 90% confidence interval of the all-mature

material. When the juvenile wood content reached

50%, the edgewise bending and tension results were

significantly different from that of the all-mature ratio.

The normalized strength results for the Southern Pine

material are shown in Figure 8. As discussed previously, the Southern Pine material was much more variable than was the Douglas-fir. The inclusion of 57%

low-grade core material seemed to significantly reduce

the edgewise bending strength of the test material. For

the bending tests, both flatwise and edgewise, little

distinction appeared between material with the 57%

low-grade core material and the 100% low-grade core

10

material, with the normalized ratio falling within each

other’s 90% confidence interval. However, the tension

test results closely followed the theoretically predicted

reductions in strength.

Modulus of Elasticity and Juvenile Wood

In the Douglas-fir material, the small bending and tension normalized test results for juvenile wood followed

the theoretically predicted curves (Fig. 9). For the mature 2 by 8 edgewise bending test material, the theoretically predicted curve was within the confidence

intervals of the normalized ratio. The juvenile 2 by 8

material was less sensitive to increases in juvenile wood

content than was predicted.

The Southern Pine normalized stiffness results are

shown in Figure 10. The inclusion of low-grade core
Figure 8–Normalized mean values for Southern Pine 2 by 2 edgewise and flatwise bending, 2

by 8 edgewise bending, and 2 by 4 tension strength test results compared to percentage of lowgrade core content. Solid and dashed lines represent theoretically predicted results for mature and

juvenile core material, respectively.

material seemed to dominate the resulting stiffness. For

all tests, the inclusion of 57% and more of the juvenile wood core material caused a significant decrease

in stiffness. As was the case with the strength results,

the results of including the 57% low-grade core material were not significantly different than the test results

for all low-grade core material. In all test modes, the

tension stiffness results came closest to the expected

theoretical curves.

Similarities and Differences

The test results summarized in Tables 2 and 3 indicate that (1mE) tight band material for the two species

was similar, having almost equal strength and stiffness.

However, the low-grade core material in the Douglasfir was 27% weaker than that in the Southern Pine.

The ratio of the all-low-grade juvenile material (2m)

strength to the tight band mature strength for Douglasfir averaged about 0.50 compared to about 0.75 for the

strength of Southern Pine. In contrast, the effect of

low-grade core content on stiffness was quite similar

between the two species. The ratios of low-grade juvenile wood core material (2j) to the tight band mature

material (1mE) for stiffness were almost the same and

averaged 0.68. Another major difference between the

two species occurred in the manufacturing process. The

Douglas-fir material caused fewer problems during the

manufacturing process and resulted in a less variable

product than did the Southern Pine material.

Mature and Juvenile Low-Grade Material

For the combinations where comparisons could be

made, strength and stiffness of the mature low-grade

material (2m) were consistently greater by an average

11
Figure 9–Normalized mean values for Douglas-fir 2 by 2 edgewise and flatwise bending, 2 by 8

edgewise bending, and 2 by 4 tension stiffness results compared to percentage of low-grade core

content. Solid and dashed lines represent theoretically predicted results for mature and juvenile

core material, respectively.

of 22% than were the strength and stiffness of the juvenile low-grade material (2j) (Tables 2, 3). The strength

and stiffness values for the juvenile low-grade material, with the exception of the Douglas-fir 2 by 2 flatwise bending 50% (2j) stiffness results, were less than

the strength and stiffness values for the mature lowgrade core. The average ratio of all-juvenile low-grade

core material (2j) to all-mature low-grade core material

(2m) for both species was consistent at about 0.8 for

strength and stiffness.

Flatwise and Edgewise Bending

In the Douglas-fir, the flatwise bending strength values

of specimens, made up of one grade of material, were

about 11% less on average than were the edgewise specimen values. However, the MOE values were generally

the same for flatwise and edgewise specimens. As ex12

pected from theory, an increase in low-grade core content had little effect on the Douglas-fir flatwise material test results until 50% of the low-grade core content

was exceeded; then the strength and stiffness decreased

dramatically. We also noted in the Douglas-fir edgewise specimens that the inclusion of 25% juvenile wood

core material had little effect on strength and stiffness

(Table 2).

In the Southern Pine material, the flatwise MOR values

were consistently 5% less than were the edgewise MOR

values, with all the various combinations of material.

In most cases, the edgewise MOE values for the Southern Pine material were also slightly greater than were

the flatwise MOE values. However, there was far less

agreement with theory. Strength was only slightly reduced as a result of including 57% of the low-grade core

in the flatwise and edgewise specimens.
Figure 10–Normalized mean values for Southern Pine 2 by 2 edgewise and flatwise bending,

2 by 8 edgewise bending, and 2 by 4 tension stiffness results compared to percentage of lowgrade core content. Solid and dashed lines represent theoretically predicted results for mature

and juvenile core material. respectively

Tensile Properties and Juvenile Wood

Juvenile wood affected tensile strength and stiffness

differently. A definite species difference was noticed between the ratios of all juvenile wood (2j) and the all

tight band material (0.55 and 0.7 for Douglas-fir and

Southern Pine, respectively, Tables 2, 3). Although juvenile wood had a similar effect on the ratio of stiffness

for the two groups (both approximately 0.7), the effect

of increased low-grade core content on the normalized

mean values for UTS and tensile MOE for both species

related closest to theory. All tension test results closely

followed the predicted results from a rule of mixtures.

A -25% increase in low-grade core material resulted in

a proportionate reduction in expected strength and

stiffness.

Size Effect

The ratio of large to small mean MOR values was consistent for Douglas-fir and Southern Pine and averaged

0.84, with the exception of 100% juvenile wood for

the Douglas-fir material (Tables 2, 3). The all-juvenile

Douglas-fir material had a ratio of 0.66. Also, the data

showed that the MOE values for Douglas-fir increased

slightly with specimen size. For the Southern Pine material, MOE was affected little, with a slight tendency

for the 2 by 8 specimens to be lower in MOE than the

2 by 2 specimens. The overall average ratio for large

to small specimen mean MOE values for Douglas-fir

and Southern Pine was 0.98. The large specimens consistently had lower variability than did the 2 by 2

specimens.

13
Sharp and Suddarth (1991) showed that generally for

composite lumber, volume effects can be reasonably

predicted with the weak-link theory. In their approach,

they demonstrated that volume effects are sensitive to

strength variability. As variability increases, the volume

effect also increases. When the thickness and span to

depth ratio of the beams are held constant, the theoretical bending volume (Kb

) can be expressed in terms of

depth (d) alone:

Kb = (d1/d2)2/B

where

Kb is the volume adjustment factor,

d1 depth of initial volume,

d2 depth of final volume, and

B the shape parameter exponent.

Figure 11–Normalized mean values for Douglas-fir 2 by 8 remanufactured bending, strength,

and stiffness results compared to percentage of low-grade core content. Dashed lines represent

theoretically predicted results for juvenile core material.

This work was not designed to determine a shape pa- The majority of tests failed in tension within the wood

rameter for LVL. However, our results of 0.84 appear between the load heads (see Appendix D). All edgewise

reasonable when compared to 0.836 for the past histor- bending test specimens failed between or at the load

ical shape parameter used on clear wood based on an heads, with the majority failing within the wood and

exponent of 1/9 (Bohannan 1966) or the current ad- not at the overlapping veneer joint. The flatwise bendjustment used for the LVL product Micro-lam of 0.803 ing test failure characteristics were noticeably different

based on an exponent of 0.136 (Council of American than those of the edgewise bending tests. Shear failures

Building Officials 1990). Because the general trend is and failures outside the load heads occurred only in the

to increase COV with increasing proportions of juvenile flatwise bending tests. Joints were critical in the tenwood, it is likely that volume effect will be more pro- sion tests. The largest number of joint failures occurred

nounced in the juvenile material. The all Douglas-fir in the tension test specimens.

14

results (Table 2) supported this concept and the Southern Pine results (Table 3) did not, but the sample size

was small for the Southern Pine large bending specimens.

Remanufactured Edgewise Bending Specimens

Results of the bending tests on the remanufactured

specimens, which were produced only for the Douglasfir, are shown in Figure 11. The MOR results of the

remanufactured billets followed the expected theoretically predicted curve well. However, the MOE results

appeared to be offset upward by 5% from the theoretically predicted results. No procedural explanation was

found for this offset.

Failure Codes and Warp Characteristics
Measurements for warp were taken on all 2 by 8 edgewise bending specimens to investigate the effect an increased proportion of juvenile wood would have on LVL

material. No warpage was detected for the various proportions of low-grade core material, whether it was mature or juvenile. A different result may have occurred if

mature and juvenile low-grade core material had been

mixed within a billet instead of concentrated symmetrically in the core.

Value Effect

The 1mE material produced was chosen to represent

the typical strength and stiffness of material produced

by LVL manufacturers. The test result obtained from

the inclusion of juvenile wood material allows for a preliminary look at what the economic impact of increased

juvenile wood would have on production of LVL. Several combinations of veneer and other costs, at various

mixtures of juvenile and mature materials, using the

strength and stiffness results from Tables 2 and 3, are

found in Appendix E, Table El.

We assumed that the customer would be willing to pay

a unit price regardless of the juvenile content as long

as the LVL product satisfied current performance requirements. The amount of increased volume needed to

compensate for the low-quality juvenile material was

determined by expanding the width or depth of the

original test specimens to produce members of the same

load-carrying or deflection capacity as the 1mE material for the same test mode. The calculation procedure

used to establish values is discussed in Appendix E. Table El allows a manufacturer with an understanding of

fixed cost to estimate the value of the juvenile veneer

for a given mixture and determine at what point it is

inadvisable to add further juvenile material.

For example, a producer knows that veneer costs are

60% of total costs. The Douglas-fir 2 by 2 edgewise

bending data suggest that if one expects to span the

same distance, having the same depth, carrying the

same load, with a 50% juvenile core, then the volume

of the member must be increased by 17% to produce

the expected strength. Other costs are assumed to remain constant and directly proportional to the volume

processed. An additional falldown rate of 20% in lowgrade juvenile veneer during manufacture was assumed

in these calculations. The data in this study suggest

that a producer can obtain juvenile wood veneer at a

cost per unit of 0.25 relative to the current price of 0.60

per unit of mature veneer. Thus, veneer costs of the juvenile wood supply must be 58% less than the current

veneer costs to break even.

If the same 2 by 2 edgewise specimen is needed to deflect a similar amount as the current manufactured material, a 6% increase in volume is needed, resulting in a

relative juvenile veneer cost per unit of 0.41, compared

to the 0.6 currently paid. This would suggest that to

maintain a similar deflection the veneer costs of the juvenile wood supply must be 32% less than the current

supply to break even.

If other costs dominate the unit cost, the increased juvenile wood material required to meet performance conditions can also cause the relative value of the juvenile

veneer to become negative, as demonstrated by the 2

by 4 tension results. This indicates that at a certain ratio of veneer costs to other costs, it would be impossible

to maintain current performance strength and stiffness

levels with an influx of low strength and stiffness core

material.

Conclusions

The results of this study give insight into the effect

that anticipated future wood resources will have on

LVL manufacturing practices. Including more juvenile

material in the veneer supply is a situation that can be

handled with current technology, but the technology

has much room for improvement. In this study, both

veneer sources represented rapidly grown material. The

Douglas-fir veneer source represents a lower bound on

the quality of the veneer sources that are anticipated.

The Southern Pine veneer material represents the typical quality expected in rapidly grown Southern Pine

veneer supplies. The results of this study indicate the

following:

It is possible to manufacture an LVL type product

with structural integrity using significant quantities of juvenile wood veneer, but design values would

be less than those currently in use. However, our

Douglas-fir tests indicate that including 25% proportions of juvenile wood in the core of LVL has little effect on the overall strength and stiffness of the

LVL.

LVL stiffness for Douglas-fir and Southern Pine react similarly to inclusion of juvenile material. However, the strength of Douglas-fir is affected more

by the inclusion of juvenile material than is that of

Southern Pine.

A significant difference exists between material manufactured with mature or juvenile material having

the same nondestructive grade. For both Southern

Pine and Douglas-fir, the ratio of juvenile to mature material with the same nondestructive grade is

approximately 0.8 for strength and stiffness.

The two techniques of nondestructive grading used

in this study are capable of indicating the low

quality of veneer sheets and placing them into low

grades. These techniques, however, are unable to

15
differentiate between low-grade mature and juvenile

material.

For the material we examined, no detectable differences were noted in the warp characteristics of the

test material with increasing juvenile wood content.

The addition of juvenile wood has a significant effect on the costs of manufacturing LVL capable of

maintaining current performance. Unless the rapidly

grown resource can be harvested at a low cost, increased member sizes will have an adverse impact on

the economics of the LVL industry. During veneer

preparation, the low strength of the juvenile wood

veneer and high number of checks in both species led

to a significant increase in breakage during handling

when compared to normal veneer losses. The falldown rate nearly doubled. The amount of juvenile

wood acceptable to manufacturers will be heavily

influenced by production costs.

Future Considerations

This study suggests a number of areas for improvement

in the manufacturing process of LVL. The low strength

of the juvenile wood veneer in both species led to significant increases in breakage during handling compared

to normal veneer. The effect of this would be an increase in cost, the magnitude depending on the proportion of juvenile wood used and the relative cost of the

veneer in the finished product. Better ways of drying

and handling juvenile veneer are necessary to reduce

the large falldown expected. To improve handling, a

better method is needed to detect juvenile wood material prior to processing. If the high resin content observed in this study is typical of Southern Pine juvenile wood, improved manufacturing techniques to handle anticipated difficulties will have to be developed.

Finally, accurate estimates are needed of how much

rapidly grown material will enter the market place.

Acknowledgments

We acknowledge the generous contributions of The

Great Southern Plywood Corporation for peeling and

drying the Southern Pine veneer, Boise Cascade Company for peeling the Douglas-fir material, Trus Joist

Corporation for drying, grading, manufacture, and

transportation of the LVL material, and Washington

State University, Wood Engineering Laboratories, for

their expert assistance in the testing of the LVL material.

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17
Appendix A-Specimen Preparation

Appendix A details the billet and strip cut-up procedure used in manufacturing the test specimens. The

billets were cut into strips and labeled with an identification code at the LVL manufacturing plant. The

strips were then transported to the laboratory facility

and conditioned prior to being cut up for specimens.

Cutting Strips

A total of 118 2-ft by 1.5-in. by 12-ft Douglas fir and

32 4-ft by 1.5-in. by 12-ft Southern Pine billets were

manufactured at the LVL plants. The 12-ft-long billets

were ripped into strips of specified widths according

to the patterns shown in Figures Al. For Douglas-fir,

each of the 110 billets (15 each of class 1mE and 2j; 16

each of 2m, D25j, D50j, D50m, and D75j) were cut into

five 144-in.-long strips that were 3.5, 3.5, 7.4, 3.5, and

3.5 in. wide. Each of the eight remaining class 1mE

and 2j billets (four each of class 1mE and 2j) were cut

into six strips that were 2, 3.75, 5.5, 2, 3.75, and 5.5 in.

wide. These strips were reassembled in various combinations to produce 1.5- by 7.25- by 144-in. remanufactured R specimens using an adhesive.

For Southern Pine, each of the first 28 billets (4 of class

1mE; 6 each of class 2m, 2j, D57j, and, D57m) were

cut into 11 strips that were 3.5, 3.5, 7.4, 3.5, 3.5, 3.5,

3.5, 7.4, 3.5, 3.5, and 3.5 in. wide, respectively. Each of

the four remaining class 1mE and 2j billets (two each)

were cut to be remanufactured to produce the R specimens. They were cut into 12 strips that were 2, 3.75,

5.5, 2, 3.75, 5.5, 2, 3.75, 5.5, 2, 3.75, and 5.5 in. wide

(Fig. A2).

For both species, the completed strips were sent to

Washington State University’s Wood Engineering Laboratories for specimen preparation and testing.

Specimen Cut-Up Procedure

Prior to cutting the specimens, all strips from the manufacturing plants were conditioned to equilibrium in

a climate-controlled room under 65% relative humidity and 75°F (approximately 12% equilibrium moisture content). Afterwards, the strips were cut to produce matched edgewise and flatwise 1.5- by 1.5- by

30-m. bending (2 by 2), 1.5- by 3.5- by 96-m. tension

(2 by 4), and 1.5- by 7.4- 144-in. (2 by 8) edgewise

bending specimens from each billet according to a cutting pattern meant to maximize the variability between

specimens that are cut from the same billet while using

all the material produced.

The Douglas-fir strips cut (Fig. A2) were remanufactured by gluing one 2j core strip between two mature

1mE strips. The material was glued so that the veneer

sheets were oriented vertically. Three mixtures of 2j

core were manufactured (25%, 50%, and 75%). In the

Southern Pine material, a considerable amount of material was discarded as a result of delamination blows

in the center of the billets. This resulted in an inadequate number of specimens for the initial test matrix.

Therefore, we used the strips cut up for remanufacture (Fig. A2) to supplement the remaining dedicated

test material. The Southern Pine remanufactured strips

were cut in a pattern similar to the material shown in

Figure Al.

18
Appendix B-Data Summary Tables

Figure Al-Cutting patterns for type 1mE, 2m,

2j. and D billets.

Appendix B contains results of the moisture content,

specific gravity, strength, and stiffness tests for the

combinations of various grades of veneer. For each

species, size, and low-grade core content combination, the sample size, mean, standard deviation, coefficient of variation, minimum, 5th percentile, 25th percentile, median, 75th percentile, and maximum values for specific gravity and moisture content are given

(Table B1). The same distributional information is also

given for strength and modulus of elasticity test results

in Tables B2 and B3, respectively.

Figure A2–Cutting patterns for remanufactured

R specimens.

19
Table B1—Distributional data for specific gravity and moisture content

Coefficient

Percentile distribution

Test

Identi- Low-grade

fication core (%)

Sample Average of Minisize (lb/in 2

) variftion mum 5 25 50 75

Maximum

Douglas-fir

2 by 2 moisture 1mE 0 60 12.1 2.7 11.2 11.5 12.0

content, % D25j Juvenile 25 64 11.9 4.0 10.8 11.1 11.6

D50j Juvenile 50 64 12.3 2.9 11.4 11.7 12.1

D50m Mature 50 64 11.8 2.9 11.0 11.2 11.5

D75j Juvenile 75 64 12.5 2.0 11.6 12.0 12.3

2j Juvenile 100 60 11.9 2.2 11.5 11.5 11.7

2m Mature 100 64 11.9 3.6 9.9 11.3 11.7

2 by 4 moisture 1mE 0 60 11.9 3.5 11.0 11.3 11.6

content, % D25j Juvenile 25 64 11.6 3.8 10.8 10.9 11.3

D50j Juvenile 50 64 13.0 12.5 10.8 11.3 11.9

D50j Juvenile a50 54 12.4 7.0 10.8 11.3 11.8

D50m Mature 50 64 11.9 3.8 10.9 11.0 11.6

D75j Juvenile 75 64 12.1 2.9 11.0 11.4 11.8

2j Juvenile 100 60 12.2 3.0 11.1 11.3 12.1

2m Mature 100 64 11.5 3.0 10.9 11.2 11.4

2 by 8 moisture 1mE 0 15 11.4 2.2 11.0 — 11.2

content, % D25j Juvenile 25 16 11.3 4.6 10.6 — 10.9

D50j Juvenile 50 16 11.6 3.1 10.9 — 11.4

D50m Mature 50 16 11.0 3.0 10.4 — 10.7

D75j Juvenile 75 16 12.2 3.5 11.6 — 11.8

2j Juvenile 100 15 11.4 2.9 10.8 — 11.2

2m Mature 100 16 11.5 4.5 10.8 — 11.2

2 by 8 remanu- R25j Juvenile 25 8 11.5 1.9 11.2 — 11.3

factured R50j Juvenile 50 8 11.7 5.4 11.0 — 11.1

moisture R75j Juvenile 75 8 11.3 2.5 10.9 — 11.0

content, %

2 by 2 specific 1mE 0 60 0.517 5.4 0.45 0.47 0.50

gravity D25j Juvenile 25 64 0.516 5.2 0.47 0.47 0.50

D50j Juvenile 50 64 0.483 5.2 0.43 0.43 0.47

D50m Mature 50 64 0.509 5.4 0.46 0.47 0.49

D75j Juvenile 75 64 0.464 5.2 0.42 0.42 0.45

2j Juvenile 100 60 0.449 6.2 0.39 0.41 0.43

2m Mature 100 64 0.497 5.3 0.44 0.46 0.48

Southern Pine

2 by 2 moisture 1mE 0 51 12.0 3.3 11.3 11.5 11.7

content, % D57j Juvenile 57 31 11.9 3.7 11.3 11.3 11.5

D57m Mature 57 48 11.7 3.6 10.9 11.0 11.5

2j Juvenile 100 36 11.7 3.6 11.1 11.1 11.4

2m Mature 100 50 11.9 3.1 11.2 11.3 11.7

2 by 4 moisture 1mE 0 50 11.8 5.7 10.5 10.7 11.3

content, % D57j Juvenile 57 23 11.9 5.6 10.8 10.8 11.3

D57m Mature 57 54 11.8 6.2 10.2 10.7 11.3

2j Juvenile 100 35 11.6 6.8 10.1 10.4 11.0

2m Mature 100 45 11.8 4.6 10.2 11.0 11.4

2 by 8 moisture 1mE 0 8 11.9 3.6 11.5 — 11.5

content, % D57m Mature 57 8 11.9 2.9 11.4 — 11.5

2j Juvenile 100 5 13.1 10.8 11.4 — 11.6

2m Mature 100 9 11.9 1.0 11.8 — 11.8

2 by 2 specific 1mE 0 51 - 0.63 3.2 0.59 0.60 0.62

gravity D57j Juvenile 57 31 0.60 5.3 0.53 0.54 0.57

D57m Mature 57 48 0.62 4.9 0.55 0.58 0.60

2j Juvenile 100 36 0.59 6.2 0.51 0.53 0.57

2m Mature 100 50 0.59 4.9 0.52 0.54 0.57

a

2 by 4 tension test results with specimens having greater than 15% moisture content were dropped.

12.2 12.3 12.7

12.0 12.3 13.0

12.4 12.6 13.1

11.8 12.1 12.4

12.5 12.6 13.1

11.9 12.1 12.6

11.8 12.1 12.8

11.9 12.2 13.2

11.7 12.0 12.5

12.4 13.9 17.7

12.3 12.6 14.5

11.8 12.2 12.8

12.1 12.2 13.1

12.2 12.4 13.0

11.7 11.7 12.6

11.3 11.5 11.9

11.2 11.7 12.3

11.6 12.0 12.2

11.0 11.2 11.7

12.1 12.5 13.0

11.4 11.6 12.0

11.4 12.0 12.4

11.5 11.6 11.9

11.4 12.3 12.6

11.3 11.6 11.7

0.51 0.53 0.61

0.52 0.54 0.60

0.48 0.50 0.57

0.51 0.53 0.57

0.46 0.48 0.51

0.45 0.47 0.52

0.50 0.52 0.56

12.0 12.3 13.1

12.0 12.3 13.0

11.7 12.0 12.8

11.6 12.1 12.8

11.9 12.1 12.7

11.7 12.2 13.7

11.9 12.4 13.2

11.6 12.2 14.5

11.5 12.1 13.8

11.8 12.2 13.1

12.0 12.2 12.8

11.9 12.2 12.3

13.5 14.4 14.6

11.9 12.0 12.1

0.63 0.65 0.67

0.60 0.62 0.66

0.62 0.64 0.70

0.60 0.62 0.67

0.59 0.61 0.66

20
Table B2—Distributional data on bending and tensile strength properties

Test

Identi- Low-grade

fication core (%)

Douglas-fir

2 by 2 edgewise

MOR

2 by 2 flatwise

MOR

2 by 4 UTS

2 by 8 edgewise

MOR

2 by 8 remanufactured MOR

Southern Pine

2 by 2 edgewise

MOR

2 by 2 flatwise

MOR

2 by 4 UTS

2 by 8 edgewise

MOR

Percentile distribution

Coefficient

Sample Average of

size (lb/in 2) variation

Mini- Maximum 5 25 50 75 mum

1mE 0 60 9,853 7.6 8,110 8,412 9,303

D25j

9,990

Juvenile 25 64 9,293 9.4 7,180 7,918 8,705 9,255

D50j Juvenile 50 64 7,167 11.7 4,040 5,538 6,805 7,210

D50m Mature 50 64 8,344 9.9 6,640 6,830 7,663 8,555

D75j Juvenile 75 64 6,688 12.6 4,260 5,265 6,220 6,715

2j Juvenile 100 60 5,502 16.0 3,320 4,060 4,853 5,525

2m Mature 100 64 6,454 22.6 3,140 5,495 5,495 6,470

1mE 0 60 8,926 11.7 6,540

D25j Juvenile 25 64 9,267 13.2 5,040

D5Oj Juvenile 50 64 8,190 13.6 5,160

D50m Mature 50 64 8,699 11.5 6,730

D75j Juvenile 75 64 7,538 11.3 5,740

2j Juvenile 100 60 4,899 21.5 2,600

2m Mature 100 64 5,716 24.3 1,810

7,043

7,128

6,085

7,055

5,920

3,111

3,132

8,262 8,965

8,440 9,075

7,490 8,120

7,810 8,780

6,905 7,670

4,068 4,790

4,868 5,760

1mE 0 60 7,105 11.5 5,150 5,930 6,492 7,045

D25j Juvenile 25 64 6,543 12.3 4,630 5,295 6,028 6,565

D50j Juvenile 50 64 5,266 11.6 3,300 4,042 4,925 5,360

D50j Juvenile a50 54 5,172 11.5 3,300 3,935 4,855 5,255

D50m Mature 50 64 5,785 9.9 4,530 4,678 5,412 5,775

D75j Juvenile 75 64 4,319 10.7 3,270 3,480 3,995 4,370

2j Juvenile 100 60 3,024 11.8 2,360 2,434 2,745 3,020

2m Mature 100 64 3,921 10.6 2,900 3,145 3,652 3,965

1mE 0 15 8,489 6.2 7,530

D25j Juvenile 25 16 8,029 12.7 6,940

D50j Juvenile 50 16 6,428 14.1 5,100

D50m Mature 50 16 7,074 8.9 6,180

D75j Juvenile 75 16 5,358 14.5 3,830

2j Juvenile 100 15 3,607 9.4 2,870

2m Mature 100 16 5,265 12.1 4,110

— 8,070 8,410

— 7,318 7,750

— 5,833 6,340

— 6,578 7,095

— 4,855 5,575

— 3,320 3,650

— 4,720 5,190

R25j Juvenile 25 8 8,074 8.2 7,290

R50j Juvenile 50 8 7,939 11.2 7,100

R75j Juvenile 75 8 6,755 8.7 5,670

— 7,518 8,010

— 7,605 7,630

— 6,325 6,920

1mE 0 64 10,191 13.4 6,450 7,618 9,498 10,220

D57j Juvenile 57 46 8,119 19.3 4,440 4,924 7,292 8,115

D57m Mature 57 58 9,218 14.1 5,140 6,665 8,310 9,580

2j Juvenile 100 54 7,527 16.9 3,760 5,070 7,068 7,630

2m Mature 100 50 9,206 12.5 5,740 6,580 8,510 9,310

1mE 0 64 9,646 14.6 5,580 7,018 8,695 9,880

D57j Juvenile 57 46 7,852 26.5 2,850 3,846 6,418 7,710

D57m Mature 57 58 9,019 17.4 4,860 6,073 7,870 9,080

2j Juvenile 54 6,943 25.2 2,870 3,310 5,940 7,325

2m Mature 100 49 8,584 20.0 5,070 5,400 7,690 8,530

1mE

D57j

D57m

2j

2m

0

Juvenile 57

Mature 57

Juvenile 100

Mature 100

50 7,426 16.8 5,280 5,494 6,460 7,245

23 6,440 15.0 4,660 4,688 5,610 6,480

54 6,907 15.1 5,190 5,455 6,080 6,835

35 5,206 14.0 3,930 4,082 4,570 5,230

45 6,395 17.3 4,250 4,532 5,500 6,220

1mE 0 8 9,062 5.9 8,270

D57m Mature 57 8 7,814 12.4 6,680

2j Juvenile 100 5 6,664 6.4 5,940

2m Mature 100 9 7,751 13.3 6,370

— 8,425 9,285

— 6,872 7,595

— 6,340 6,780

— 6,795 7,640

10,340 11,390

9,788 11,280

7,638 8,900

8,928 10,080

7,300 8,530

6,193 7,310

7,633 9,080

9,805 10,830

10,160 11,560

8,888 10,500

9,385 10,650

8,035 9,600

5,650 7,320

6,890 7,860

7,580 9,100

6,995 8,330

5,748 6,420

5,620 6,210

6,200 7,040

4,710 5,030

3,260 3,960

4,210 4,670

8,950 9,450

8,435 11,100

6,930 9,020

7,355 8,500

5,868 6,450

3,750 4,170

5,865 6,160

8,452 9,300

8,118 10,000

7,275 7,310

11,118 12,560

9,208 11,510

10,220 11,280

8,360 10,080

10,005 11,260

10,765 12,610

9,165 12,970

10,078 11,840

8,292 9,890

9,950 13,100

8,482 10,500

6,980 8,370

7,450 9,370

5,780 6,880

7,115 9,360

9,415 9,690

8,855 9,270

6,930 7,060

8,530 9,510

a

2 by 4 tension test results with specimens having greater than 15% moisture content were dropped.

21
Table B3—Distributional data for modulus of elasticity

Test

Identi- Low-grade

fication core (%)

Percentile distribution

Coefficient

Sample Average of Mini- Maxisize (× 106

 lb/in2) variation mum 5 25 50 75 mum

Douglas-fir

2 by 2 edgewise

MOE

2 by 2 flatwise

MOE

2 by 4 tensile

MOE

2 by 8 edgewise

MOE

1mE 0 59 1.857 11.2 1.356 1.592 1.709 1.827 1.961 2.528

D25j Juvenile 25 64 1.781 9.5 1.315 1.537 1.673 1.757 1.869 2.257

D50j Juvenile 50 64 1.558 6.7 1.314 1.380 1.480 1.564 1.629 1.880

D50m Mature 50 64 1.742 6.1 1.498 1.529 1.682 1.752 1.811 1.989

D75j Juvenile 75 64 1.428 7.9 1.209 1.225 1.364 1.428 1.481 1.836

2j Juvenile 100 60 1.302 10.1 1.042 1.108 1.210 1.292 1.386 1.663

2m Mature 100 64 1.589 11.2 1.195 1.326 1.473 1.561 1.689 2.311

1mE 0 58 1.975 12.7 1.627 1.649 1.827 1.916 2.001 2.726

D25j Juvenile 25 64 1.891 10.0 1.449 1.574 1.767 1.872 2.022 2.396

D50j Juvenile 50 63 1.882 8.5 1.549 1.625 1.750 1.904 2.003 2.261

D50m Mature 50 63 1.791 7.8 1.449 1.552 1.687 1.815 1.884 2.129

D75j Juvenile 75 64 1.612 8.1 1.324 1.416 1.502 1.628 1.694 2.004

2j Juvenile 100 60 1.299 14.4 0.855 1.029 1.148 1.294 1.435 1.791

2m Mature 100 64 1.601 15.6 1.202 1.219 1.435 1.572 1.761 2.388

1mE 0 60 1.870 6.9 1.659 1.676 1.766 1.852 1.929 2.193

D25j Juvenile 25 64 1.757 5.8 1.519 1.589 1.671 1.752 1.839 1.950

D50j Juvenile 50 64 1.580 5.0 1.389 1.417 1.530 1.581 1.636 1.752

D50j Juvenile a50 54 1.587 5.0 1.389 1.431 1.530 1.586 1.641 1.752

D50m Mature 50 64 1.675 4.8 1.511 1.520 1.625 1.692 1.737 1.878

D75j Juvenile 75 64 1.440 6.5 1.255 1.326 1.366 1.433 1.490 1.781

2j Juvenile 100 60 1.239 6.1 1.045 1.143 1.197 1.239 1.270 1.572

2m Mature 100 64 1.574 5.5 1.421 1.430 1.509 1.574 1.625 1.822

1mE 0 15 1.896 4.3 1.770

D25j Juvenile 25 16 1.837 7.3 1.681

D50j Juvenile 50 16 1.667 5.7 1.498

D50m Mature 50 16 1.725 5.1 1.485

D75j Juvenile 75 16 1.482 7.2 1.322

2j Juvenile 100 15 1.165 8.7 0.994

2m Mature 100 16 1.580 4.9 1.444

— 1.813 1.909 1.961 2.029

— 1.735 1.838 1.881 2.218

— 1.632 1.649 1.694 1.935

— 1.699 1.730 1.780 1.850

— 1.386 1.496 1.580 1.670

— 1.130 1.148 1.166 1.469

— 1.527 1.587 1.636 1.697

2 by 8 remanufact- R25j

ured MOE R503

R75j

Southern Pine

2 by 2 edgewise

MOE

2 by 2 flatwise

MOE

2 by 4 tensile

MOE

2 by 8 edgewise

MOE

Juvenile 25 8 1.994 3.6 1.938

Juvenile 50 8 1.954 4.6 1.827

Juvenile 75 8 1.732 6.1 1.644

— 1.950 1.958 2.054 2.136

— 1.891 1.932 2.039 2.091

— 1.662 1.716 1.784 1.887

1mE 0 64 1.980 9 13.6 1.324 1.520 1.809 1.977 2.121 2.792

D57j Juvenile 57 46 1.566 2 14.8 0.930 1.183 1.414 1.578 1.728 2.051

D57m Mature 57 58 1.726 5 14.2 1.151 1.585 1.585 1.724 1.822 2.407

2j Juvenile 100 54 1.342 1 14.2 0.926 0.992 1.228 1.345 1.480 1.794

2m Mature 100 50 1.743 1 14.4 1.183 1.569 1.569 1.752 1.919 2.289

1mE 0 64 1.886 14.5 1.080 1.715 1.715 1.930 2.048 2.506

D57j Juvenile 57 46 1.488 22.1 0.889 0.972 1.256 1.420 1.678 2.354

D57m Mature 57 58 1.794 12.2 1.316 1.484 1.637 1.776 1.978 2.306

2j Juvenile 100 54 1.267 17.6 0.815 0.918 1.117 1.242 1.401 1.786

2m Mature 100 49 1.698 16.8 0.955 1.170 1.528 1.683 1.838 2.687

1mE 0 50 1.973 9.6 1.492 1.586 1.890 2.013 2.102 2.321

D57j Juvenile 57 23 1.692 11.0 1.336 1.338 1.514 1.728 1.827 1.987

D57m Mature 57 54 1.763 7.5 1.464 1.535 1.678 1.760 1.869 2.074

2j Juvenile 100 35 1.388 11.8 1.154 1.156 1.279 1.326 1.543 1.762

2m Mature 100 45 1.673 13.1 1.152 1.212 1.536 1.697 1.825 2.148

1mE 0 8 1.733 5.8 1.543

D57m Mature 57 8 1.529 11.6 1.215

2j Juvenile 100 5 1.264 4.0 1.220

2m Mature 100 9 1.719 7.9 1.522

— 1.647 1.769 1.804 1.840

— 1.402 1.554 1.680 1.743

— 1.225 1.250 1.310 1.350

— 1.570 1.776 1.841 1.850

a

2 by 4 tension test results with specimens having greater than 15% moisture content were dropped.

22
Appendix C-Cumulative Frequency Distributions

Appendix C provides comparison plots of cumulative frequency distributions for strength and stiffness test results

for the four different tests (flatwise and edgewise 2 by 2 bending, 2 by 4 tension, and 2 by 8 edgewise bending) conducted on each species. Figure C1 shows the strength results for various combinations of low-grade core materials for

the Douglas-fir bending and tension tests. Figure C2 shows the Southern Pine strength results for the bending and

tension tests on low-grade core material combinations. The MOE cumulative frequency results for Douglas-fir are

shown in Figure C3. Figure C4 shows the Southern Pine MOE results for the various test sizes and combinations of

low-grade core material.

Figure C1–Cumulative frequency distributions for Douglas-fir strength test results for various

combinations of low-grade core materials.

23
Figure C2–Cumulative frequency distributions for Southern Pine strength test results for various

combinations of low-grade core materials.

24
Figure C3–Cumulative frequency distributions for Douglas-fir MOE results for various combinations of low-grade core material.

25
Figure C4–Cumulative frequency distributions for Southern Pine MOE results for various combinations of low-grade core material.

26
Appendix D-Failure Code Summary

Failure code information was collected on all tests; a

three-digit failure code was used. The first digit represents failure location. Failures were categorized as failing at, between, or outside the load heads. The second

digit of the failure code represents the type of failure

observed: tension, compression, or shear. The third

digit was an attempt to classify the cause of failure.

Failures were determined to be a result of knots, joints,

slope of grain, wood, or compression wrinkling rather

than tension, compression wrinkling, or glueline. Table

D1 summarizes the failure code information collected

during testing.

27
Table D1—Douglas-fir and Southern Pine LVL testing failure codes

Speci- Low-grade

Failure code

a

Test mens core (%) 111 112 113 114 115 121 122 124 126 134 137 211 212 213 214 224 225 226 231 232 

Douglas-fir

2 by 2

edgewise

MOR

2 by 2

flatwise

MOR

9 2 42 1 1 4 1

4 1 43 1 15

1 42 21

1 43 1 19

3 2 42 2 1 14

3 1 30 1 22 

3 3 45 3 10

1 18 1 1 2 6 

4 1 21 1 1 1 1 1 1 8 1 

4 2 38 1 9 1 

2 37 2 11 5 3 

1 41 1 18 3

7 1 1 26 1 2 3 16 

4 2 29 1 2 1 2 1 21 

27 32 1

18 45 1

17 37

27 37

19 45

18 1 37 4

30 3 1 3

7 1 4 3

1 0 5 

13 3

10 1 4 

16

9 6

14 2

2 by 4

tensile

UTS

2 by 8

edgewise

MOR

1mE 0

D25j Juvenile 25

D50j Juvenile 50

D50m Mature 50

D75j Juvenile 75

2j Juvenile 100

2m Mature 100

1mE

D25j

D50j

D50m

D75j

2j

2m

0

Juvenile 25

Juvenile 50

Mature 50

Juvenile 75

Juvenile 100

Mature 100

1mE 0

D25j Juvenile 25

D50j Juvenile 50

D50m Mature 50

D75j Juvenile 75

2j Juvenile 100

2m Mature 100

1mE

D25j

D50j

D50m

D75j

2j

0

Juvenile 25

Juvenile 50

Mature 50

Juvenile 75

Juvenile 100

2m Mature 100
Table D1—Douglas-fir and Southern Pine LVL testing failure codes-con.

Speci- Low-grade

Failure code

a

Test mens core (%) 111 112 113 114 115 121 122 124 126 134 137 211 212 213 214 224 225 226 231 2

Southern Pine

2 by 2

edgewise

MOR

1

1

1 1

2 by 2

flatwise

MOR

42

3 3

1 37

42

37

27

20

38

26

29

50

23

51

35

45

7

8

4

9

21

13

21

12

12

20 1 1

13

4 3 1

18

5 1 2

3

1

1

2 by 4

tensile

UTS

2 by 8

edgewise

MOR

1mE 0

D57j Juvenile 57

D57m Mature 57

3 Juvenile 100

2m Mature 100

1mE 0

D57j Juvenile 57

D57m Mature 57

2j Juvenile 100 1

2m Mature 100

1mE 0

D57j Juvenile 57

D57m Mature 57

2j Juvenile 100

2m Mature 100

1mE 0

D57m Mature 57

D57m Juvenile 100

2m Mature 100

aFirst digit is location: 1, between load heads; 2, at load heads; 3, outside of load heads.

Second digit is type of failure: 1, tension; 2, compression; 3, shear.

Third digit is cause of failure: 1, knot; 2, joint; 3, slope of grain; 4, wood; 5, compression rather than tension; 6, compression wrinkling; 7, glueline.
Appendix E-Economic Analysis

The 1mE material produced represented typical

strength and stiffness of material produced by LVL

manufactures. The test results obtained from the inclusion of juvenile wood material allows for a preliminary look at what will be the economic impact that increased juvenile wood in the resource will have on LVL

production. Different combinations of production and

veneer cost at various mixtures of juvenile and mature

materials using the strength and stiffness results from

Tables 2 and 3 are tabulated in Table El. It is assumed

that the customer purchasing the LVL product is willing to pay a unit price regardless of the juvenile content

as long as the LVL product will satisfy current performance requirements. The amount of increased volume

needed to compensate for the low-quality juvenile material was determined by expanding the width or depth of

the original test specimens to produce members of the

same load-carrying or deflection capacity as the 1mE

material for the same test mode. Table El can be used

by a manufacturer to roughly estimate the value of the

juvenile veneer for a given mixture and determine at

what point it is inadvisable to add further juvenile material.

The calculations are defined as follows:

Rm + Rj = 1 and Cm + Cv + Cj ·(1+w)

= 1 (unit price)

Zr = strength of the D billet/1mE strength

Ze = stiffness of the D billet/1mE strength

where

Cm is manufacturing costs

Cv is veneer costs for product with all high-quality

veneer

Cj is veneer costs required for juvenile material to

produce one unit

Zr is relative strength of juvenile wood (from

Tables 2 and 3)

Ze is relative stiffness of product containing juvenile

wood

Rj is relative amount of low-grade material in the core

Rm is relative amount of mature wood on faces

(1 - Rj)

w is percentage of additional low-grade material lost

in processing

Relative volume of the material needed for new products containing juvenile wood was calculated as follows.

the beam is made with additional depth. The

section modulus and the moment of inertia increase, causing the volume required to increase

as follows:

where

Vr is relative volume needed for new product containing juvenile wood

If the member is in place flatwise or is acting

as a tension member to meet the performance

requirement, the beam is made wider. Thus,

only the area of material is increased, causing

the volume to increase as follows:

Vr = 1/Zr = 1/Ze (increases the area of member)

Manufacturing costs were determined by assuming

manufacturing costs are proportional to volume.

Vr · CM = new manufacturing costs

1 - Vr · Cm = value of veneer

Rm · Vr · Cv = value of high-grade veneer

Cj = (1 - Vr · Cm) -

Rm · Vr · Cv = value of low-grade veneer

Therefore, the cost per unit for

high-grade core = (Rm · Vr · Cv)/(Rm · Vr) = Cv

low-grade core = [(1 - Vr · Cm) - Rm · Vr ·

Cv]/Rj · Vr · (1 + w)

= [{l - Vr · (Cm + Rm) · (1 -

Cm)}]/[Vr · (1 - Rm)(1 + w)]

The overall new unit cost would be

Unit cost = 1 = Vr · Cm + (Vr · Cv · Rm) +

[Vr · (1 + w) · Cj · Rj]

If the member is acting as an edgewise bending

member to meet the performance requirement,

30
Table El-Economic analysis of the relative worth of juvenile veneer

per unit volume for other veneer cost combinations

Performance criteria

Juvenile

veneer (%)

Value of juvenile veneer

per unit costa

0.6 0.5 0.4 0.3

Veneer Other cost

Low-grade/ volume

1mE needed 0.4 0.5 0.6 0.7

Douglas-fir

2 by 2 edgewise bending

Strength

Stiffness

2 by 2 flatwise bending

Strength

Stiffness

2 by 4 tension

Strength

Stiffness

2 by 8 edgewise bending

Strength

Stiffness

Southern Pine

2 by 2 edgewise bending

Strength

Stiffness

2 b y 2 flatwise bending

Strength

Stiffness

2 b y 4 tension

Strength

Stiffness

2 b y 8 edgewise bending

Strength

Stiffness

Veneer cost

aUnit cost = 1.

31

*U.S. GOVERNMENT PRINTING OFFICE: 1993-746-040/80004