Department of

Agriculture

Service

Southeastern Forest

Experiment Station

General Technical

Report SE-53

Robert H. McAlister
March 1989

Southeastern Forest Experiment Station

p.0. Box 2680

Asheville, North Carolina 28802
The Research and Development

of COM-PLY Lumber

Robert H. McAlister

Research Forest Products Technologist

Forestry Sciences Laboratory

Athens, Georgia

ABSTRACT

Between 1974 and 1986, a Southeastern Station Research Work

Unit developed standards for composite studs, joists, and truss

lumber and manufactured and demonstrated the materials. Economic feasibility was considered in every stage of research. Further

development is left to industry.

KEYWORDS: Construction lumber, composite lumber, truss lumber,

joists, studs, performance standards.

The characteristics of U.S. timber supplies have

changed markedly in recent decades, and further

changes are coming. Within 10 years, half of our

softwood timber will be coming from trees that were

planted (USDA Forest Service 1982). We have roughly

470 million acres of forest land. Softwoods occupy

200 million acres and hardwoods 270 million acres

(USDA Forest Service 1974b) (fig. 1). Most of the

hardwoods are in the East, close to the major

construction markets, but these markets are almost

exclusively softwood. Almost two-thirds of the annual

timber cut of 12 to 13 billion board feet (USDA Forest

Service 1982) goes into the construction, remodeling

and repair of buildings (fig. 2). Most of the wood that

goes into construction is softwood. That means that

there is a lot of pressure on the softwood timber

resource. A major problem is to find some means of

using more hardwoods in construction.

A second problem is utilization. We do not use

our timber efficiently. When we harvest a stand of

timber, we bring only about 70 percent of the wood

volume to the mill (Koenigshof 1977). We leave the

small, crooked, or rotten trees and trees of undesirable

species in the woods.

Figure 1. -Acreage of coniferous and hardwood forests in the continental United States.
17%

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AND PALLETS ‘i

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Figure 2. -How wood is consumed in the United States; 1970 data.

Of the 70 percent brought to the sawmill, only

about 45 percent is recovered as lumber (Koenigshof

1977) (fig. 3). The same factor applies to plywood

plants. Forty-five percent of 70 percent is a little over

30 percent. We recover a lot of the waste in secondary

products and fuel, but, at best, we are using only 50

to 60 percent of stand volume.

As early as 1972 many people could see that

there was likely to be a serious softwood timber

supply problem in the United States by the year

2000 (USDA Forest Service 1974b). The pressure on

the softwood resource would create shortages and

rising prices. We needed to develop structural

products that utilized more than 30 percent of the

stand volume and used both hardwood and softwood

timber in structural lumber and panel products.

It appeared that some type of composite product

had the best chance of meeting the major goals.

Most of the stress on both framing and structural

panels is concentrated on the outermost fibers. It

makes sense to put the strongest, stiffest wood on

the outside and put the lower quality material on the

inside. One solution is to glue strong stiff veneers

cut from the outer portions of the best trees to a

particleboard core made from ground-up particles of

wood and bark from the lower quality and less

desirable trees. This concept was the basis for

COM-PLY (fig. 4) (Koenigshof 1977).

LES

Figure 3. -Conversion of logs into sawed lumber. Figure 4. -The composite structural lumber concept.

2
Originally, we calculated that 15 percent veneer

would be enough to give us the strength and stiffness

that we needed for structural framing. What is more,

it appeared that hardwoods would be suitable for

both the veneer facings and the particleboard core.

When a log is sawed into boards, much of the

strongest, stiffest, clearest, highest density wood

from the outside of the tree is turned into chips,

slabs, and edgings. Meanwhile, a high proportion of

the wood from the center of the tree becomes lumber,

even though the wood is knotty, less dense, and

contains juvenile wood, which may cause warp and

twist when the lumber is dried.

COM-PLY takes the strong, stiff, high-density

wood from the outer portion of the tree stem and

uses it where it can add maximum strength and

stiffness to the composite lumber or panel. The lower

quality wood from the center of the stem goes into

the particleboard core, and 90 percent of the log

ends up in the high-value primary product.

The concept is neat and elegant, but 15 years

ago no one was sure that it would work. In 1973, the

Department of Housing and Urban Development

(HUD) gave a research grant to the USDA Forest

Service to look into the COM-PLY concept. The work

was assigned to a small Research Work Unit (RWU)

of the Southeastern Forest Experiment Station located

in Athens, GA. The COM-PLY work was headed

initially by Richard F. Blomquist and, after Blomquist’s

retirement, by Gerald A. Koenigshof. The members

of the research team and their areas of expertise

were: Dorothy H. Costa and Priscilla L. Floyd, Project

Secretaries; John E. Duff, wood/moisture relations

and fire; Louis I. Gaby, preservative treatments and

fastener corrosion; Nolan Malcolm, Physical Science

Technician; Robert H. McAlister, mechanical properties and forest resources; Charles B. Vick, adhesives

and gluing; Roy M. Walker, Physical Science Technician; Dick C. Wiienberg, fasteners and mechanical

testing; and Harold F. Zornig, engineering uses.

This report describes the research team’s approaches and the findings. Information is provided in

three sections, The first briefly outlines the subject.

The second describes research on COM-PLY studs

through the pilot-plant production run and the

demonstration houses that used only the 2 by 4

studs. The third describes the development of

COM-PLY joists, COM-PLY truss lumber, and an

improved flakeboard core.

Outline of Progress

We started by looking at residential framing and

at the least critical structural member, the stud. A lot

of the structural lumber in a house frame is in studs

or other 2 by 4’s, and we thought we had a good

chance of producing a COM-PLY stud that would

perform at least as well as the studs that were being

sold in the marketplace. The first question was ‘What

should a COM-PLY stud look like?’ We decided that

it should be solid, 1.5 by 3.5 inches, and fully

compatible with traditional construction practice for

cutting and fastenings (fig. 5).

The next question was ‘How good does a stud

have to be?’ That was a bigger problem because no

performance criteria existed for studs. Studs were

studs. The first suggestion, by HUD, was that the

COM-PLY stud had to be as good as a lodgepole

pine stud. We looked at the grading rules and the
CONCENTRATED BENDING LOADS

REACTION Y---‘--l REACTION

4 b

90’ 11 4,

I- -1

Figure 6.-Schematic of loading method for combined bending test and end-loading.

published engineering design values for lodgepole

pine (WWPA 1978) and figured that we could meet

the criteria with very little problem. In fact, we decided

to try to do a little better, since at that time very few

lodgepole pine studs were being sold. Our first job,

then, was to develop the performance standards for

composite studs.

The approach we used was to select a standard

house, 30 feet wide and two stories high, and apply

Federal Housing Authority (FHA) suggested design

loads to the roof, floors, and side walls (Blomquist

and others 1978). Studs were spaced 16 inches on

center in the first-story walls and 24 inches on center

in the second-story walls. Loads for individual studs

were then determined by standard engineering

procedures. It turned out that the second-story studs

24 inches on center were the most critical with an

axial load of 1 ,190 pounds and a bending load of 40

pounds per linear foot (due to wind). These loads

were used to develop strength performance criteria.

Deflection criteria were developed for combined

loading of 1 ,190 pounds axial compression and 30

pounds per linear foot bending (see fig. 6 for loading

diagram). Maximum allowable deflection was l/240

of the test span of 90 inches or 0.375 inch (Blomquist

and others 1978).

In the performance standards for composite

studs, we developed a formula to account for

variability, repetitive member loading, a factor of

safety, and the difference between the lo- to 15-minute

loading of test specimens and the long-term loading

of members in service. This expression became

known as the HUD formula because key features of

the variability adjustments were proposed by Howard

C. Hilbrand, an engineer with FHA-HUD. The HUD

formula is presented in figure 7.

HUD Allowable Design Load Formula

LOAD

t,,s

-

t

m

.05

allow

where:

x = average load

t

.05 = t.,,for n-l d.f.

S = standard deviation

N = number of samples

F, = repetitive member (1.15)

F, = factor of safety (1.5)

F, = time of test factor (1.18)

Figure 7.-The HUD formula for calculating allowable design loads for engineering properties of composite structural lumber.
Another criterion of performance is durability.

The original thinking was that composite studs might

be exposed to the weather for up to a year due to

construction delays. Therefore the composite studs

should retain most of their strength and stiffness

after 1 year of unprotected direct exposure to the

environment. One-year tests were not practical for

evaluation of alternative materials, but there were no

widely recognized accelerated tests to simulate 1

year of outdoor weathering. However, the ASTM

D1037 6-cycle accelerated aging test (ASTM 1979)

was accepted as simulating several years of outdoor

weathering for particleboards. One cycle of this

procedure involves soaking in 200 “F water, freezing

at 10 OF, drying at 210 OF, steaming at 210 OF, and

drying again at 210 OF. We decided that if the

composite studs retained at least 50 percent of their

strength and stiffness after the 6-cycle D1037 test,

they would be sufficiently durable.

Dimensional stability was also part of the performance standard for composite studs. The consensus

was that composite studs, after soaking and drying,

should exhibit changes of dimension in width,

thickness, length, and warp that did not exceed the

comparable values for sawed studs.

If we had done nothing more than develop

performance standards for studs, the research would

have been worthwhile. But, we did much more. All

through the process we tested components and

different combinations of components to see how

close we could come to meeting our own performance

standards. We also analyzed softwood and hardwood

timber resources to see if there was enough material,

particularly high-quality veneer, to make manufacture

of composite studs feasible, while utilizing all, or

nearly all, of the timber in typical stands (McAlister

and Clark 1983; McAlister and Taras 1978).

Two problems were evident at the start. The first

problem was a suitable particleboard core. No one

was producing a phenolic binder particleboard l-1/2

inches thick, and the only phenolic particleboards

that were being produced had a density of 55 to 65

pounds per cubic foot (PCF). Boards of that density

split when nails are driven into the ends. We found

some medium-density urea binder boards that were

about right at 40 to 42 pounds PCF. It turned out

that a density of 38 to 42 PCF was a practical optimum

for all properties. Eventually we had some

1-l/2-inch-thick phenolic board made to order in a

particleboard plant in southern Georgia. The second

problem was with the percentage of veneer required

in the composite stud. We had originally assumed

that two plies of l/8-inch veneer on each edge of

the stud would be sufficient. In order to meet the

deflection criieria of 0.375 inch deflection for a load

of 40 pounds per linear foot over a span of 90 inches,

we had to use at least two plies of l/&inch veneer

on each edge. That meant that studs would be 20

percent veneer and 80 percent particleboard. The

resource studies indicated that there was enough

southern pine grade C and better veneer in typical

stands to support the manufacture of composite

studs with enough left over to utilize the tops to a

4-inch diameter.

By 1974, we had developed a composite stud

that looked very promising. We were anxious to

evaluate it on site in building trials. The first pilot-plant

run was made to produce some 3,000 studs (Vick

1977a). This limited run and the demonstration houses

built with the studs were a success. The COM-PLY

studs were used and handled just like standard

studs. A demonstration house was constructed at

each of four locations: Columbia, MD; Aurora, IL (fig.

8); Vancouver, WA; and Augusta, GA (Koenigshof

and others 1977). Builders commented favorably.

They noted, however, that the COM-PLY studs were

heavier (11 pounds vs. 9 pounds for spruce) and

that the 8-percent phenolic binder in the particleboard

dulled ordinary steel saw blades very quickly.

Figure 8. - COM-PLY studs were used in demonstration houses

using standard construction practices.

5
Figure 9. - COM-PLY veneer-faced truss lumber and COM-PLY 2 by 6 studs and plates were used in the NAHB Research Foundation

EER-II house in Damascus, MD, in 1982.

A lot more research remained to be done. We

were convinced that we could develop satisfactory

COM-PLY joists, and COM-PLY truss lumber seemed

a good possibility. We hoped COM-PLY could be

used for all the structural framing in residential

construction, but these uses had not yet been studied.

In addition, building code officials, engineers, and

architects were asking many questions that we could

not answer. They asked about fire resistance,

acoustical qualities, creep under long-term loading,

and probable costs in relation to sawed lumber. And

we still had not looked at the potential of the hardwood

resource.

These questions occupied us from 1975 through

1986, when the Composite Research RWU was

terminated. We had some big milestones along the

way. Our joist work was far enough along so that a

demonstration house was built in Marietta, GA, in

1978 that used COM-PLY joists, COM-PLY studs,

and COM-PLY panels for subfloor and roof sheathing.

Performance standards were developed and used to

evaluate the composite joists in that home (Duff and

others 1978).

Our search for improved fire resistance in

COM-PLY floor joists led to the development of a

homogeneous, fully oriented strandboard that turned

out to be the key for the commercial development of

composite structural lumber. This development was

in cooperation with Tom M. Maloney and Roy Pellerin

of Washington State University (Peters 1988). The

stiffness of the fully oriented strandboard was three

times that of the randomly oriented flakeboards.

Particle orientation increased the modulus of elasticity

(MOE) of composite joists from 1 .l million pounds

per square inch (PSI) to 1.6 million PSI, which is

comparable to the MOE of No. 2 southern pine.

Another accomplishment was the Energy Efficient

Residence II (EER-II) (fig. 9) that was designed and

built by the National Association of Home Builders

Research Foundation in Damascus, MD, in 1982. We

fabricated composite studs, composite floor joists,

composite truss lumber, and special foundation

grade (FDN) 2 by 6 studs treated with chromated

copper arsenate for the EER-II all-weather wood

foundation. Thus, we demonstrated that composites

could be used as framing anywhere in residential

construction.

6
We found that we did not need to limit the veneer

used to the higher grades. Grade D veneer of both

pine and hardwoods was acceptable if certain

guidelines were followed (McAlister 1983). This

discovery made the full utilization of existing timber

for COM-PLY a definite possibility.

We determined that hardwoods could be used in

composite structural lumber almost interchangeably

with southern pine. In fact, yellow-poplar and sweetgum veneers proved superior to southern pine veneers

in some respects (McAlister 1979; McAlister 1982).

The yield of veneer from the hardwoods is a little

less than from the pine, but use of hardwood veneer

makes it possible to fully utilize the timber containing

mixtures of pine and hardwoods (McAlister 1980).

We showed that composite lumber made with a

fully oriented strandboard core was suitable for

trusses. The loading properties for truss plates in

oriented flakeboard are slightly lower than those for

truss plates in southern pine, but the loads are well

within the useful range of design values (McAlister

1986).

The timber supply and utilization problems seen

in 1972 stjll exist, and we are beginning to have

problems with the fast-grown plantation trees (Megraw

1985). The petroleum shortages have been delayed,

but they seem inevitable. The cost of phenolic resins,

which are petrochemicals, is an important determinant

of the cost of composite structural products. Nevertheless, composite structural materials hold much

promise for the future. They could change forest

management in major ways.

Composite Studs: Concept to Reality

The research effort on composite framing materials

grew out of a Housing RWU. The mission of this unit

was ‘More effective use of wood in housing.’ Work

on innovative framing materials was underway in

1968 when Zornig designed the FS-SE-5 house that

used a spaced Gothic-arch rafter made from 1 by

2’s and 2 by 4 blocks (Anderson and Zornig 1972).

Vick did some exploratory work on spaced columns

that combined 1 by l’s or 1 by 2’s with hardboard

webs.

In early 1972 the Housing RWU was looking for

new areas of research. The unit had developed several

designs for low-cost housing which used traditional

wood-framing materials quite efficiently. The plans,

which had been published by the U.S. Government

Printing Office, were ‘best sellers.” We were told to

develop a new mission statement that would be

more concerned with the problems associated with

the use of southern woods in building construction.

Gerald Koenigshof, from the Washington Office,

USDA Forest Service, Division of Economics, came

to Athens to discuss a concept he had developed

for combining veneer with particleboard. Koenigshof’s

presentation was illustrated with professionally

prepared drawings originally used for a TV program

produced and shown in the Washington, DC, area.

These illustrated the problems of a shrinking resource

base, smaller trees, inefficient conversion of trees to

lumber and plywood by conventional processing,

and the underutilization of hardwood species in

construction.

Koenigshof had presented the composite concept

to Orville G. Lee and Howard C. Hildebrand of

FHA-HUD. They committed $400,000 to study the

concept if a satisfactory research unit was willing to

undertake the work. Koenigshof had approached the

Forest Products Laboratory at Madison, WI, with the

proposal, but its resources were already fully committed to other high-priority research studies. The

members of the Housing RWU team in Athens were

convinced that the composite concept had merit and

that there was a good chance of solving most of the

problems within 5 years. The $400,000 from FHA-HUD

would provide a large share of the operating funds

needed to study the concept. Also, the unit had

acquired from excess properly a

120,000-pound-capacity universal test machine. This

large machine made it possible to do the full-scale

testing of structural members that would be required.
The final decision to begin work on the concept was

made by Blomquist, the Project Leader, with the

approval of the Southeastern Forest Experiment

Station.

The scope of the RWU’s original mission was

quite limited. Our goal was to produce a vertical

framing member-a stud- 92-5/8 inches long that

would be capable of supporting both vertical building

loads and bending loads due to wind in the same

manner as sawed studs made from species such as

Douglas-fir, southern pine, spruce, or fir. There were

no restrictions on size or shape, but the new stud

was supposed to be made from wood-based materials.

A stud was chosen as the framing member because

it was considered to be the least critical structural

member in residential construction.

Research on structural composite panels, an

integral part of the total research effort, was the

responsibility of the American Plywood Association.

It was given a research grant from FHA-HUD funds

received by the Forest Service. This research proceeded concurrently with the work on studs.

Once the decision to undertake the research

had been made, the problem was analyzed and a

research direction developed in a series of meetings

between the Housing Research staff and Koenigshof.

Personnel from FHA-HUD were also involved both in

person and in telephone conferences. It was decided

that the new stud would be the same size (1.5 by

3.5 inches) as existing sawed studs and that dimensional stability would have to be comparable to sawed

studs, at least in the 3.5-inch dimension.

The term ‘COM-PLY” was not coined until a year

later. Initially, we referred to the stud as ‘the new

stud’ or ‘the synthetic stud.’ These terms became a

problem because we did not want to develop a bad

image for the product before it had a chance to

prove itself. The term ‘COM-PLY” was developed in a

brainstorming session with all of the research staff

participating. The term ‘COM-PLY” was later copyrighted by the American Plywood Association-with no

objection from the Forest Service-since we felt that

it could better regulate the use of the term.

Another decision made at this time was that the

major objective would be the development of the

COM-PLY stud and that results of the research would

be published in some son of manual rather than as

individual reports scattered through the literature.

The major effect of this approach was that studies

were planned to answer specific questions related to

the eventual manufacture of the product. In many

studies, the number of samples and the statistical

design were inadequate for publication of the results.

We did make rapid progress, but there was very little

optimization and some questions were bypassed . . once a workable solution was found.

At the start of the research we made a list of all

of the problems that we recognized and the approximate order in which answers were needed. This

exercise was valuable, but we were fortunate in finding

as we went along that many of the anticipated

problems either did not exist or had already been

solved. This phenomenon is sometimes referred to

as ‘luck.’

From the start, we needed and got a team effort.

We realized that all parts of the problem had to be

solved at about the same time. The research assignments were very loose and were made principally on

the basis of previous work in a particular area. Work

on the veneer resource, the particleboard core, the

fastener and end use problems, and the gluing of

veneer to the particleboard core was conducted at

the same time. We got together regularly to discuss

the progress of the work. Everyone knew what

everyone else was doing. This constant crossfertilization of ideas and approaches to problems

made the work go a lot faster. Plus, we could always

count on help.

This report presents some results of the unpublished studies to prevent their loss and to show the

sequence of progress. An understanding of the

sequence is important because a perfectly acceptable

composite stud was developed, produced in a

pilot-plant operation, and extensively tested in

demonstration houses with involvement of the major

building codes about 2 years after the research

began.

At the outset, there were no real standards for

the strength and stiffness of sawed studs. Studs

were being produced and sold from species as diverse

as Douglas-fir with an average MOE of 1,700,OOO PSI

and lodgepole pine with an average MOE of 950,000

PSI. Grading rules for Stud grade 2 by 4’s were

quite specific on such matters as size, moisture

content, warp, crook, bow and wane; there was not

a word about minimum strength or stiffness.

The ultimate marketability of the COM-PLY stud

was a constant concern. We knew that particleboard

8
had a reputation for poor durability and quality. By

adopting the ASTM D-l 037 g-cycle, accelerated

aging test, we went out of our way to ensure that

there was no question of the durability of the COM-PLY

stud.

Initially, it appeared that there were five major

areas of research required.

1, The quantity and quality of veneer available

from trees in typical stands. As part of this problem,

some decision needed to be made about the quality

and quantity of veneer required to produce a stud

with the required strength and stiffness. We wanted

to be sure that the veneer and the material for

particleboard were in reasonable balance so that

additional residues would not be produced. This

problem was assigned to McAlister.

2. The physical characteristics of the particleboard core of the composite. In 1972, particleboard

made with phenolic binders was a rarity and no one

was producing a particleboard l-1/2 inches thick.

The characteristics of the particleboard would determine the quality and thickness of the veneer required

and would affect the dimensional stability of the

composite stud. Dimensional stability was deemed

to be critical so that sawed studs and the new studs

could be used interchangeably in the same wall

system. This problem was assigned to Duff.

3. The fastening characteristics of the new

studs. We wanted the new studs to be completely

compatible with nails, screws, and other devices and

with traditional practices of construction. This problem

was assigned to Zornig.

4. The adhesive bond between the veneer

edges and the particleboard core. This problem

was assigned to Vick.

5. The economics of the manufacture of

COB&PLY studs. This area included resource

availability, plant design and layout, cost of raw

materials, labor costs, etc. This problem was assigned

to Koenigshof.

Blomquist was responsible for the overall planning

and direction of the research effort. Koenigshof, after

his transfer from the Washington Office to Athens,

was assigned as a team leader for structural considerations and testing procedures.

Resource Studies

Several simplifying assumptions were made at

the start of these studies. We assumed that grade C

and better veneer would be required for the edges

of the COM-PLY studs. The maximum open defect

allowed for C grade veneer is l-1/2 inches, and any

larger defect seemed excessive for 1 -l/2-inch-wide

structural lumber. We also assumed that three layers

of veneer would be required to sufficiently randomize

the defects to produce a uniform strength and stiffness

of the COM-PLY studs. The first resource studies

were limited to southern pine because veneer yields

by grade were available by l-inch diameter classes

for loblolly and slash pines (Clark and Schroeder

1971; Phillips and others 1979; Schroeder and Clark

1970). Data had been collected on veneer yields by

block and by tree. The objective of these studies

had been the development of yield equations related

to tree diameter and height. It was necessary to

analyze the data from a different perspective to obtain

the information that we needed for the composite

stud work. Clark, Phillips, Taras, and Saucier from

the Utilization of Southern Timber RWU in Athens,

GA, were quite generous in sharing the raw data,

even to the extent of giving us a complete set of

data cards.

These data were combined with data from the

Southeastern Station’s Forest Inventory and Analysis

RWU on the number of trees in each diameter class

by stand type. The results showed that almost all of

the C grade veneer in southern pine comes from the

first three blocks in the stem. This analysis also showed

that there was enough C and better grade veneer in

the first three blocks of trees in average stands of

southern pine to completely utilize the entire stem

(to a 2-inch-diameter top) in the production of the

COM-PLY studs. In fact, a small surplus was available

to provide veneer edges for particleboard made from

some of the trees classified as ‘culls’ in typical stands.

The next questions were concerned with the

MOE of veneer cut from southern pine trees of various

diameters. MOE is a measure of stiffness of materials

and permits calculation of deflection of structural

members under load. We needed to know the average

MOE of the veneer and also whether the MOE was

normally distributed. Measuring the MOE in bending

of veneer proved to be difficult. We adapted the

techniques developed by Koch and Woodson (1968)

to estimate the dynamic MOE of veneer by measuring

the transit time of a stresswave through a veneer

strip. Koch and Woodson gave us a great deal of

veneer that had been stresswave tested for the

lamination study and had not been used. This

9
pretested veneer speeded up our work considerably

in preparing studs for testing. A study was designed

in cooperation with the Utilization of Southern Timber

RWU in Athens to collect loblolly pine veneer from a

previously planned study of veneer yield by grade.

Veneer was collected from each block just after

roundup, in the middle of the peel, and just before

the core was dropped. Over 600 veneer strips 1.5 by

100 by 0.167 inches thick were tested for dynamic

MOE at the Forest Products Laboratory in Madison,

WI (McAlister 1976). We found that the MOE of the

loblolly pine veneer averaged about 1.8 million PSI,

that the stiffest veneer came from the second block

in the tree, and that the distribution appeared to be

normal. Normal distribution simplified subsequent

projections and analysis of the resource.

We did a short study to determine whether we

needed three plies of veneer or if two plies on each

edge were sufficient. We found that differences in

strength and stiffness between studs made with two

plies or three plies of veneer were not of practical

significance. These results meant that we could use

thicker veneer and fewer gluelines to produce the

studs.

The effects of using lower grade veneers and of

different methods for laminating plies on the strength

and stiffness of the studs were studied intensively.

Results indicated that at least half of the D grade

veneer from loblolly pine could be used if care was

taken that one of the plies was of C grade veneer.

This finding meant that suitable veneer could be

taken from more of the low-grade pine and hardwood

trees in typical stands and that utilization of timber

for COM-PLY studs could approach 100 percent of

stand volume. It also became apparent that short

grain in the veneer was the limiting factor in the

strength of the composite. Short grain was as likely

to occur in clear veneer as in veneer of the lower

grades.

The effects of variations in the MOE of the

particleboard core on the strength and stiffness of

COM-PLY studs were also studied. The particleboard

that we were using as a core material at that time

had an MOE of between 250,000 and 450,000 PSI.

Results indicated that variations in the MOE of the

particleboard did not significantly affect the MOE of

the composite. The only significant factor was variation

in the MOE of the veneer component.

Particleboard Research

There were several immediate problems with the

particleboard core. From the start, the COM-PLY

studs were intended to be fully weatherproof. One of

the initial requirements was that the studs retain at

least 50 percent of their strength and stiffness.after 1

year of outdoor exposure. We needed a particleboard

with a phenolic binder. The only phenolic particleboard

available was a special II-B-2 mobile-home decking

5/8 inch thick with a density of about 60 PCF. To

match the thickness of sawed studs, we needed a

particleboard that was 1.5 inches thick. Initial steps

involved gluing together three thicknesses of l/2-inch

particleboard or using two plies of 5/8 inch and one

ply of 3/8 inch in the center. The thickness swelling

of the laminated particleboard was close to 30 percent.

We found one company in the East that was making

an extruded board 1.5 inches thick. This board

disintegrated when soaked in water. We were told

that a phenolic particleboard 1.5 inches thick would

be impossible to produce economically because the

cure time would be at least 25 minutes.

One company on the west coast was making

particleboard 1.5 inches thick for door core stock

using a urea binder. This material was produced in

two densities, 28 PCF and 42 PCF. Tests of this

material were encouraging. Thickness swell was only

about 20 percent-way too much but closer to

acceptable than previously tested materials. We

made up several studs with this core material and

even exposed some to outdoor weathering on a test

fence. The COM-PLY studs made with the urea binder

particleboard cores lost only about 20 percent of

their initial strength and stiffness after 1 year of outdoor

exposure.

We continued to negotiate with particleboard

plants to produce some 1.5-inch-thick phenolic binder

board. No plant was willing to guarantee the level of

internal bond, MOE, modulus of rupture, or thickness

swell. Blomquist finally contracted with a major

particleboard producer for a one-shift production

run. The plant operators would try their best to meet

our specifications with the phenolic binder, but we

would have to take what we got and the price was

$10,000. It worked out very well in the end, but we

were pretty worried. The problem was that urea

binders have a lot of ‘tack” (stickiness) and phenolic

binders have very little tack. After the mat was formed

and before it went to the prepress, it had to be

transferred from one conveyor belt to another. Since

there was so little tack and the mat for a 1.5-inch-thick

board was so thick and heavy, the mat cracked and

10
broke during transfer. For a couple of hours all the

mats were run back into the surge bins and there

were no boards going into the hot press. Eventually

the percentage of phenolic resin binder was raised

to 8 or 9 percent rather than the 6-percent target

value. The mats held together and particleboard

started coming out of the presses. The press time

was rather long -20 minutes- but it was expected.

We ended up with two flatbed truckloads of particleboard. Thickness swell of this board was about 10

percent; the MOE was about 450,000 PSI with an

internal bond of 80 to 100 PSI. Density of the board

was about 42 PCF, which turned out to be ideal. Our

gamble had paid off handsomely; this core material

was used in the pilot-plant production run. We knew

for the first time that we were likely to be successful

in producing a COM-PLY stud that would meet all of

the standards that we had set. This milestone was

very important.

Compatibility With Traditional Construction

The residential construction industry is highly

traditional. New products are accepted reluctantly,

especially if they require new and special techniques,

tools, or fastening procedures. We wanted the

COM-PLY stud to be as close to sawed studs as

possible in appearance, performance, and use. The

COM-PLY stud should require no special fastenings.

In practice, this meant that it had to be nailable with

conventional nails.

We had predicted that a major fastening problem

would be splitting when nailing through the veneer

edges and into the particleboard core with 6d and

8d common nails. It turned out that the most serious

problem was splitting of the ends when the studs

were end-nailed to the plates with 16d common or

16d sinker nails. The 60 PCF particleboard we had

laminated together to make 1.5inch-thick core

material split so severely that there was no nail

withdrawal resistance.

A great deal of ingenuity and effort went into

developing special fastener systems to attach the

studs to the plates. One method used a modified

joist hanger arrangement. Another used a crimped,

folded, toothed plate (like a small truss plate) that fit

into a grooved plate. Later we noted that the

28-PCF-density and 42-PCF-density urea door core

boards did not split when end-nailed with 16d common

nails. The 28-PCF-density board had very low

withdrawal resistance, but withdrawal resistance for

the 42-PCF-density board was quite acceptable.

Several other limited tests confirmed that particleboards in the 38 to 42-PCF-density range did not

split when end-nailed and gave acceptable withdrawal

values. Particleboards in this density range could

also be toe-nailed into the plates with 8d common

nails.

The 38 to 42-PCF-density range for the particleboard core material is a critical specification so that

conventional fasteners can be used.

Gluing Veneer to the Particleboard Core

We anticipated trouble in laminating the veneer

to the particleboard core because the two materials

have completely different dimensional stability characteristics. The joint must resist the differential swelling

of the veneer and particleboard and still be able to

transfer horizontal shear forces from the veneer edges

to the core. The cut edge of the particleboard is

quite porous and not a good gluing surface. The flat

grain southern pine veneer has wide bands of

latewood, which is also a difficult gluing surface. It

looked like an insoluble problem.

However, the first thing that we tried worked very

well. We used a 100 Ib/Mft* spread of a conventional

phenol-resorcinol adhesive that cures at room

temperature. Best results were obtained with a

5minute open assembly time and a 15 to 20-minute

closed assembly time. Applied pressure of 125 PSI

and a curing temperature of 70 “F were also important.

The curing time could be reduced if the bondlines

were cured in a hot press at 300 “F.

The major disadvantage of the system was cost.

Phenol-resorcinol adhesives are relatively expensive,

compared with phenolic plywood adhesives and

phenolic binders for particleboard. We used this

adhesive system for the veneer to core bond throughout all subsequent research on the COM-PLY studs,

including the pilot-plant run that produced over 3,200

studs (Vick 1977a).

We did experiment with an emulsified polyisocyanate adhesive designed for a very rapid curing

at room temperature. This adhesive was quite effective

but more expensive and more difficult to use than

the phenol-resorcinol adhesive. We extensively tested

melamine resins, melamine-urea resin blends, and

phenolic resin molding adhesives that could be cured

rapidly with radio-frequency energy. Nothing worked

any better than the phenol-resorcinol adhesive that

we started with. This adhesive system passed both

the ASTM D-1037 g-cycle accelerated aging test and

the 1 year of outdoor exposure with practically no

delamination or loss of strength.

11
Economics of Manufacture of COMA-PLY Studs

Research on the economics of manufacture

included the development of detailed cost analyses

of the production processes for several alternative

methods of manufacture and plant layouts. Price

trends for both raw materials and studs were studied.

Detailed costs could not be estimated until the

manufacturing process was known. The economic

studies, therefore, lagged behind COM-PLY stud

development. It appeared, however, that COM-PLY

studs could be produced and sold at a profit in

competition with conventional sawed studs. Since

studs are one of the lowest priced commodities, it

appeared desirable to be able to produce other

types of structural lumber in the same plant to raise

the average price of products.

Summary of COM-PLY Stud Research

The original mission of the research was completed in June 1975 with the construction of the third

demonstration house using COM-PLY studs and

COM-PLY panels. This demonstration house was

built in Vancouver, WA, with the cooperation of the

American Plywood Association. It was completed in

time for the 1975 meeting of the Forest Products

Research Society (FPRS) in Portland, OR. Our team’s

report on the development of the COM-PLY stud and

a report of research on composite panels by the

American Plywood Association were presented at

the annual meeting (Blomquist and others 1975;

Lyons and others 1975).

This achievement was remarkable. In less than 3

years we had taken a complex idea from concept to

reality. At this point, there were no publications on

the research. A great deal of what had been learned

in the 3 years of concentrated effort was contained

in the summary report delivered by Blomquist at the

FPRS annual meeting. The format for the definitive

report on COM-PLY was not determined until the

following year when it was decided to publish a

series of individual reports with a common format to

be known as the COM-PLY series.

The decision was made at this time to extend

the mission of the research to include joists and

other structural members. The results of this research

are detailed in the following section of the report.

Joists

The decision to develop a COM-PLY joist was a

logical outgrowth of the success of the stud program.

In all development and analysis, we had considered

the stud as an end-loaded and side-loaded beam

rather than as a column with bending loads. Wellaccepted standards for structural performance of

joists existed, and we believed that we could develop

COM-PLY members that met those standards. A

problem analysis showed several areas that required

research.

1. The MOE of a joist is critical because deflection

under design load is limited to l/240 of the span

with an absolute limit of one-half inch, no matter

what the span. A target MOE of 1.4 million PSI was

set for COM-PLY (southern pine joists have an MOE

of 1.6 million PSI) so that allowable span of COM-PLY

joists would be comparable to that of sawed joists.

There was a problem connected with joist length.

Since studs are less than 8 feet long, they can be

fabricated with full-length veneers on the edges.

Joists are up to 32 feet long. This means that some

method of joining sheets of veneer (scarfing or

staggered butt joints) had to be developed and the

effect on joist stiffness and strength determined. This

area of research was assigned to McAlister.

2. Utilization of hardwoods for both veneer and

particleboard components of the COM-PLY structural

materials. Even in pine stands, there is a considerable

volume of hardwood. The use of hardwoods was an

integral part of the COM-PLY concept. There were

no data on veneer yields by grade for hardwoods.

Since most hardwoods other than oaks have lower

MOE than southern pine, there was concern over

possible performance problems of hardwood veneers

in composites. This research area was assigned to

McAlister.

3. Creep is the continued increase in the deflection

of beams with no increase in load. This problem was

potentially serious because particleboard was known

to creep. Joists would be subject to long-term bending

dead loads. This investigation was assigned to

Wiienberg under the supervision of Koenigshof.

4. The fire resistance of joists. COM-PLY studs

did not perform as well as sawed studs in fire tests.

That problem is more serious in joists than in studs

because the load-bearing requirements for floors are

more critical than for walls. Fire performance for

12
walls is limited by burn-through and load carrying

and has a 20-minute base for performance. Floors

are required to carry full design load (live and dead)

for 10 minutes. This research area was assigned to

Duff. After Duff left the project in 1981, the research

was carried on by Wittenberg under the supervision

of Koenigshof.

5. Joists have different fastener requirements

than studs. Many builders use joist hangers, others

use ledger strips. Bearing, or compression resistance

perpendicular to the joist, was seen to be a possible

problem. This research was assigned to Wittenberg.

6. The termite and decay resistance of untreated

COM-PLY joists was a matter of great concern.

Preservative treatment of joists is desirable or required

in some situations. Treatment of a structural member

that consisted of over 50-percent particleboard was

seen as a potential problem. This research was

assigned to Gaby.

7. Manufacturing COM-PLY joists economically

was a potential problem because joists require more

veneer, probably thicker veneers and more gluelines

than COM-PLY studs. A manufacturing process had

to be developed to bring particleboard, veneer cutting

and drying, and laminating technologies together to

produce a new product. This problem area was

assigned to Koenigshof.

8. The use of COM-PLY structural lumber for

light-frame wood trusses. This use was conceived

because of the large amount of structural lumber

used annually in trusses. The general properties of

COM-PLY structural lumber (dry and straight with

uniform strength and stiffness) made it desirable for

use in a highly engineered product like a truss. Initially,

the major problem was seen as the lateral-load

resistance of truss plates in the composite structural

lumber. This problem area was assigned to McAlister.

As with stud development, the major objective

was considered to be the development of the

COM-PLY joists and trusses rather than the production

of publications. The technology transfer effort was to

be concentrated on the commercialization of the

COM-PLY joist; that is, to persuade a manufacturer

to build a plant to produce COM-PLY structural lumber.

Some publications about the veneer resource studies

were in the works, but no decision had been reached

on a format for publishing the compendium of work

on the COM-PLY project. Much of the research was

interrelated. For example, decisions about the veneer

thickness required to increase joist MOE would affect

fastener performance, creep, fire resistance, treatability, and economics. Therefore all research efforts

had to be closely coordinated. Individual researchers

had to exchange information frequently.

Joist Stiffness

The first development work was concentrated on

2 by 10 (1.5 by 9.25 inch) joists. A direct scale-up

with the same proportion of veneer as on the COM-PLY

stud failed. The MOE of this joist was about 0.9 million

PSI, while the target MOE was 1.4 million PSI. Since

the MOE of the particleboard core averaged about

0.45 million PSI, the only solution was to increase

the amount of veneer on the edges of the joist.

Calculations indicated that we needed between 1.25

and 1.50 inches of veneer on each edge of a 2 by

10 to meet the stiffness requirement. Veneer would

make up 27 to 32 percent of the total volume. A

quick check of the resource data on veneer grade

yields indicated that some D grade veneer would

have to be utilized. Another problem was with the

number of gluelines. With l/8- to l/Sinch veneer, 8

to 10 gluelines would be required for each edge

lamination. These gluelines are quite expensive. One

solution was to use l/4-inch-thick veneer. The use of

l/4-inch veneer on all composite lumber would result

in a nearly constant ratio of veneer to particleboard

of 27 percent for everything from 2 by 4’s to 2 by

12’s. However, the number of gluelines would be

minimized, which would tend to minimize costs.

We could not find a veneer mill willing to peel

and dry l/4-inch southern pine veneer. The consensus

was that peeling l/4-inch veneer would tear up

equipment. It was a bit frustrating since for years

veneer mills on the west coast had peeled 5/16-inch

Douglas-fir veneer for core stock without tearing up

any equipment. Finally we found a small veneer mill

in Murphy, NC, that agreed to peel and dry some

southern pine l/s-inch veneer for us. We had to take

mill-run veneer. They would clip the material to 12

inches wide, and we would pay for the square feet

of veneer actually cut. This veneer was the basis for

most of the development work on the COM-PLY

joists,

We soon realized that the target value for MOE

of 1.4 million PSI was a bit unrealistic with the

particleboard core that we were using. An MOE of

1 .l to 1.2 million PSI was practical and within the

same stiffness range as spruce pine-fir joists that

residential builders were using in many areas.

Mechanical testing of many joists showed that if

13
joints in adjacent plies of veneer were staggered or

offset at least 12 inches, there was no effect on the

MOE of the joists and the strength (MOR) was reduced

very little. We found short grain was the most serious

veneer defect, reducing both strength and stiffness.

A great deal of otherwise clear veneer has extremely

short grain. Much of the time, the severity of the

short grain is not evident from the surface appearance

of the veneer. The dynamic MOE of the veneer

determined by stresswave techniques was an excellent predictor of joist MOE. However, even the

stresswave technique would not detect areas of

short grain in a long strip of veneer. We looked at

many alternative systems of grading veneer for use

in COM-PLY products, but we never found any system

that did a better job than the standard American

Plywood Association panel grading rules.

Many tests of COM-PLY joists indicated that, with

the number of plies of l/4-inch-thick veneer being

used in the composite beams, the grade of the veneer

did not have to be very good. We found that we

could use all of the D grade veneer if the outside ply

was of C or better grade. Since all of the veneer that

could be peeled would be usable, some source of

additional particleboard would be needed to use all

of the veneer. This development was of major

importance to the economics of manufacture for

COM-PLY.

Utilization of Hardwoods

Major questions about the utilization of hardwoods

concerned the characteristics of the hardwood

veneers-their yield by grade and their strength and

stiffness. We assumed that the particleboard furnish

for COM-PLY could be made of a mixture of softwood

and hardwood. (This was a trifle optimistic.) As nearly

as we could tell from the literature, very little research

had been done on structural characteristics of

hardwood veneers. We initiated a hardwood veneer

study in cooperation with the Utilization of Southern

Timber RWU in Athens as part of its hardwood biomass

research. Veneer yields by grade and stiffness

characteristics were determined for sweetgum,

yellow-poplar, and white oak from the Georgia

Piedmont; for yellow-poplar, white oak, and soft maple

from the North Carolina mountains; and for yellowpoplar, blackgum, and sweetgum from the South

Carolina Coastal Plain.

Each study followed the same procedure. Sites

were selected in each area as being representative

of the timber. Three trees in each l-inch diameter

class from 10 to 22 inches d.b.h. were selected from

each site. Only dominants and codominants with no

visible decay were considered. The trees were. felled,

measured, and bucked into l- or 2-block sections (a

block was considered to be 8.4 feet long). A l-inch

disk was taken at the top of each block. The trees

were weighed in the woods and then trucked to a

cooperating softwood plywood mill (the same mill

was used for all three studies). One-sixth-inch veneer

was peeled from the blocks after conditioning. A

color-code spray system was used so that the veneer

from each block could be identified when tallied for

size and grade. Each block was measured at each

end and at the center immediately before being

chucked in the lathe. Each core was measured at

each end and at the center after it was dropped. A

similar procedure had been used to determine the

yield by grade for southern pine veneer.

Veneer was taken from each block to be used

for strength and stiffness tests. The tests and the

results are fully described in published reports

(McAlister 1980; McAlister 1982; McAlister and Clark

1983).

Generally, the results of the studies were quite

favorable. The yield of veneer from the hardwoods

was somewhat less than from southern pine, but the

quality of veneer was comparable. The strength and

stiffness of the hardwood veneer were excellent.

Yellow-poplar in particular was found to have an

MOE equal to that of southern pine (McAlister 1982).

Yellow-poplar and sweetgum were found to be

completely suitable for use in structural composites.

This finding opened up the possibility of complete

stand utilization for production of COM-PLY by using

pine and mixed hardwood stands.

Other studies on the use of mixed hardwood

furnish in the particleboard core of composite

structural members were done in cooperation with

the University of Georgia and Washington State

University. The results of these studies were not

published, but they were generally favorable. Particleboard made from mixed hardwood furnish had

adequate strength and stiffness for use in composites.

14
However, the thickness swell of the hardwood furnish

particleboards was somewhat greater than for

particleboards made from southern pine furnish. This

problem was left at this stage since we did not have

facilities for this type of particleboard research. We

felt that our resources were better used on other

research.

Creep of Structural Composites

Creep-increasing deflection with no increase in

structural load-was seen as a possible problem

with COM-PLY joists, The problem is not unique to

composites. Solid sawed joists are known to creep

because of the visco-elastic nature of wood, and

particleboards used as flat panels have serious creep

problems. Creep in particleboard may be caused by

the density gradient that is a consequence of the

reactions to temperature, moisture, and pressure

gradients during the press cycle. Whatever the

mechanism, the perception was that particleboards

(and products made from them) would creep.

This problem was discussed at great length.

Two or three possible approaches to measuring

creep in COM-PLY joists resulted in study plans. In a

preliminary study, joists under load were cycled

throughseveral cycles of high temperature and relative

humidity. The conclusion was that COM-PLY joists

were no more creepy than southern pine joists. Data

from this preliminary study were not sufficient to

warrant publication. No detailed study of creep in

composite joists was installed because (1) a final

specification for the particleboard core material had

not been developed, (2) sufficient temperaturehumidity-controlled space for a large number of

specimens was not available, and (3) both money

and manpower were in short supply and had to be

used for studies of higher priority.

One limited study was installed as the result of a

deflection problem that surfaced at the EER-II test

house in Damascus, MD, during 1982. During

construction, it was noted that the outboard end of a

joist with a 2-foot cantilever had deflected almost

three-fourths of an inch after a heavy rain. The engineer

in charge of the design of the EER-II house brought

up the question of creep. A study was initiated in

haste. Two floor sections were fabricated using 2 by

10 joists spanning 14 feet and loaded to 125 percent

of design load. Deflection measurements were taken

almost continually for the first couple of hours after

the load was applied, then daily for several weeks,

then weekly for a year, and finally monthly until the

study was terminated some 5 years later. Both floor

sections survived the 125 percent of design load for

over 2 years. Finally, the joists in one of the floor

sections buckled and failed because lateral bracing

was lacking. Lateral bracing was added to the other

floor section without removing the load and the test

continued. When the load was removed, the floor

section was allowed to recover for 6 weeks. The final

deflection, after full recovery, was about equal to the

initial deflection under load. This movement was

termed ‘irrecoverable creep.’ The joists were then

removed from the floor section and tested under

static bending to failure. There was no change in

stiffness and, as nearly as could be determined, no

change in strength of the COM-PLY joists due to the

5 years of loading at 125 percent of design load.

Due to the limited nature of the study, the results

were not submitted for publication.

Fire Resistance of Joists

Fire resistance of building components, especially

naturally combustible wood-building components, is

very important. Insurance rates and the danger to

human life are major considerations. Tests of COMPLY studs for fire resistance at the Forest Products

Laboratory in Madison, WI, uncovered a problem.

Generally, the composite materials were not as fire

resistant as solid sawed materials. Most of the strength

of the composites came from the veneer on the

edges of the members. When the veneer burned

through, the member failed. The best that could be

said for the composites was that they were almost

as good as the sawed members.

This problem was especially acute for COM-PLY

joists. The fire resistance of joists is measured by

building a complete floor system over a large furnace.

The floor is loaded to design load with vats filled

with water. When the fire is started in the furnace,

the temperature rise must follow a standard curve.

Failure is measured by collapse or excessive deflection

of the floor system. In initial ASTM and Underwriter

tests, COM-PLY joists failed in 7 minutes. The unofficial

benchmark failure time for joists was 10 minutes as

established by FHA-HUD.

Obviously, these tests of complete floor systems

are quite expensive. Very few laboratories in the

United States are capable of performing them, and a

great deal of material must be shipped. We needed

15
Figure 10. -Comparative fire performance of sawn lumber and many types of composite structural materials was evaluated

in the ‘coffin fire test.’

some method of evaluating the fire resistance of

structural members that would be faster and less

costly than the full-scale tests. This was the basis for

the development of the ‘coffin fire test.’

The ‘coffin’ was a small furnace made of fire

brick. The heat source was a large two-arm pipe

burner using propane gas. The test consisted of

making up a panel 32 inches wide and 96 inches

long from 2 by 4’s covered with l/Binch gypsum

board. This panel acted as the cover to the coffin

furnace. Design load was applied at third points with

lead weights set in place with a small derrick made

from a length of pipe and a boat-trailer winch. The

initial deflection was measured with a transit using a

reference point on the panel (fig. 10). The burner

was ignited and the temperature rise was controlled

by regulating the gas-flow according to output from

quick-acting thermocouples in the furnace. Failure

was determined from transit-based deflection readings. The burner was extinguished, the panel was

removed, and the flames were doused with a garden

hose. The procedure was not a standard test, but it

did provide comparative values with known materials

and their performance in the standard test. Since the

test was quick and inexpensive, we were able to

16
determine the probable effects of many variables in

the construction of composite structural materials.

Some of the knowledge gained from the ‘coffin”

test helped during design of composite joists that

did meet the standard fire test value of 10 minutes.

We found that (1) the stiffer the veneer used in the

composite, the longer the time to failure; (2) the

higher the density of the core material, the longer

the time to failure; (3) the higher the MOE of the

core material, the longer the time to failure. It was

this last conclusion, coupled with the development

of the fully aligned particleboard core, that led to the

development of a composite joist that exceeded the

lo-minute benchmark time in a standard test.

None of the data developed from the fire tests

(the ‘coffin’ test or the standard ASTM fire tests)

were published.

Fastener Interactions

Joists have some unique fastener problems

compared with studs. End-nailing must support both

shear and moment loads (for example, around stairwell

openings) for the life of the structure. If joist hangers

are used, several small nails near the end of the joist

must support large shear loads in a very small area

of the core. Some joists act as header beams where

ledger strips nailed into the particleboard core support

heavy lateral loads.

These problems were studied by Wittenberg and

Walker for several years. Results were reported in

COM-PLY Report 20 (Wittenberg 1981).

Decay and Termite Resistance

Generally, framing materials are used in protected

environments where resistance to decay and termites

is not a major factor. However, some natural resistance

to decay and termites is desirable for any structural

material, and preservative treatment of framing lumber

is either desirable or required in some applications.

Several studies were initiated in cooperation with the

Wood Products Insect RWU, Gulfport, MS, to check

termite resistance of untreated composite floor joists.

Some natural termite resistance of the composites

was found (Gaby and Carter 1981).

The treatability of composite structural lumber

was tested. Results indicated that composite structural

lumber was easy to treat to any desired retention

with waterborne preservatives. Full penetration of the

members was achieved in less than half the time

required for southern pine lumber. Some of the

thickness swell that occurred during treatment of

composite lumber was irrecoverable on redrying, but

the swelling was not sufficient to be considered a

defect. Decay and termite resistance of the treated

composites was outstanding. Composite structural

lumber was treated with chromated copper._arsenate

to a retention level of O.£ PCF and used in an

All-Weather Wood Foundation System for the EER-II

research house in Damascus, MD. There were no

publications on this phase of the work.

Economics of Manufacture

The costs of manufacturing composite structural

materials were a constant concern. The overall

research objective was to develop a product that

could compete on a performance and price basis

against No. 2 KD southern pine dimension lumber.

This objective guided our research from the beginning,

and there were some positive benefits to this approach. Since hardwood stumpage prices are

generally lower than softwood stumpage prices,

economic considerations made research on hardwood

components more attractive. Also, costs were considered when we evaluated resin binders for patticleboard; times and temperatures for curing particleboard; the peeling, drying, and laminating of veneer;

the amount and type of waste produced at each

processing step; the amount of electrical and heat

energy required for each processing step; and the

amount of labor required for each step.

These factors, together with data on the basic

forest resource and yield factors, were incorporated

into a computer program that yielded estimates of

required inputs, amount and type of waste generated,

fixed costs, variable costs, assumed cash-flows, and

profitability. The program was developed and refined

over a period of years by Koenigshof. Results of the

detailed analysis of joist manufacture under specific

assumptions were published as COM-PLY Reports

15, 17, and 26 (Koenigshof 1978, 1979, 1983).

Seminars on the feasibility of manufacturing COM-PLY

panels in converted plywood plants were presented

in cooperation with the American Plywood Association.

Koenigshof also prepared detailed economic analyses

for several major forest products manufacturers who

were considering the feasibility of producing composite structural products.

Generally, the economic projections for composite

structural product manufacture were favorable. The

basic assumption was that composite structural

products could be sold at a price at least equal to

the average price of No. 2 southern pine dimension

lumber.

17
An Intermediate Product

A workable composite joist was developed and

tested by early 1978. Enough joists and studs were

made in the laboratory to construct a demonstration

house in Atlanta, GA, in conjunction with the 1978

Forest Products Research Society annual meeting

(fig. 11). The demonstration house incorporated

composite floor joists that were 32 feet long and

continuous over a center support. There were also

composite studs and composite panels that had

been commercially manufactured in a North Carolina

plant.

Even though a workable composite joist had

been developed, there was still a great deal of work

to be done to check alternative methods of manufacture and the effects of many process variables on

the physical and mechanical properties of the material.

The demonstration house was featured on an

FPRS-sponsored tour at the annual meeting.

Composite Truss Lumber

While research continued on the composite floor

joists, the decision was made in 1979 to explore the

development of composite truss lumber. There were

two major factors considered in this decision: (1) the

truss fabrication industry consumes about 2 billion

board feet of dimension lumber every year, and (2)

problems related to warped, twisted, and below-grade

lumber could be reduced with composite structural

lumber.

There were some immediate problems with the

concept. To begin with, the standard method of

fabricating light-frame trusses is with toothed metal

plates made from 20-gauge or 16-gauge steel plate.

The teeth are pressed into the wide face of the

dimension lumber in the truss. With the standard

configuration of composite structural lumber (i.e., the

veneer on the narrow edges) the teeth are pressed

into the flakeboard. Preliminary tests showed that

the lateral load resistance of plates installed into the

particleboard core did not yield useful design load

values. Another potential problem was with the column

buckling characteristics of the composite structural

lumber. Studs are loaded as columns, but they are

covered with sheathing or some type of panel material

that braces the column. Truss components are

Figure 11. -Composite structural joists, 2 by 10 by 32 feet long, were used in a demonstration house in Atlanta, GA.

18
sometimes loaded in compression and, because of

truss design, their ratio of length to radius of gyration

falls into the intermediate or long column range.

Preliminary tests had indicated a possible buckling

problem with composites in the intermediate column

range.

The quick fix was to redesign the composite

specifically for use in trusses. Since the biggest

perceived problem was with the lateral-load resistance

of the truss plates, we moved the veneer from the

edges of the composite to the faces so that the

truss plates would be installed into the veneer. We

hoped that moving the veneer to the wide face of

the composite would also eliminate the column

buckling problem. Moving the veneer to the wide

face would greatly increase veneer use, but the veneer

grade did not have to be as high because the stress

level would be lower. Resource analysis indicated

that if all of the D grade veneer could be used, there

would still be enough veneer available to fully utilize

the trees in a stand.

Extensive research was conducted. The lateralload resistance of truss plates installed in the

veneer-faced composite was more than adequate. In

fact, it was almost equal to the values for truss plates

installed in southern pine dimension lumber. The

lower grade veneers did not lower the strength and

stiffness of the composite if a few simple guidelines

were followed. The results of this research were

reported in COM-PLY Report 25 (McAlister 1983).

Core Material for Composite Truss Lumber

One of the requirements of the veneer-faced

composite was a different type of core material. We

needed a core that was 7/8 inch thick. In combination

with two plies of l/6-inch veneer on each face, the

finished thickness would be 1.5 inches. Also, the

dimensional stability properties of the core needed

to be unique. With the wide face of veneer, a certain

amount of linear expansion across machine direction

of the particleboard would be desirable to reduce

stresses induced by changes in moisture content.

A contract to produce a fully oriented particleboard

7/8 inch thick was negotiated with a west coast

producer. It was assumed that the fully oriented

particleboard core for which we contracted would

have somewhat improved strength and stiffness

parallel to machine direction due to the orientation of

the particles. It was also assumed that linear expansion

across the machine direction of the particleboard

would be 4 or 5 percent after 24 hours of water soaking.

Since the veneer moves about 6 to 8 percent under

these conditions, such dimensional instability would

be desirable.

We had worked closely with FHA-HUD since the

beginning of the composite structural products

research. The demonstration houses using composites had been insured under a special HUD program

for innovative use of materials. In 1981 we were asked

to take on a real challenge. FHA-HUD and the National

Association of Homebuilders Research Foundation

were cooperating in the design and construction of

a showcase Energy Efficient Residence, EER-II, near

Washington, DC. The construction was scheduled

for late spring 1982. What composite structural

materials could we supply? We agreed to produce

the truss lumber, the joists, the studs, and the

preservative treated framing for an All-Weather Wood

Foundation for the EER-II project.

This was quite an undertaking. Our testing lab

was converted to a pilot-plant operation with a layup

and clamp table 34 feet long and 4 feet wide. Everyone

in the project was involved in furious activity twice a

day as the layups were made and the pressure was

applied to the gluelines. Vick had tested extensively

a special water-emulsion isocyanate laminating

adhesive and found that a 4-hour cure time under

pressure was sufficient to produce strong durable

bonds between the veneer and the particleboard

core. Special techniques were developed to laminate

the veneer and spread the glue. The composite

joists were made full length (32 feet). Each day’s

production was checked off the bill of materials.

We had to postpone producing the truss lumber

until last because the special oriented core was not

available. On the very last day in what could be

called ‘good luck’ or ‘just-in-time inventory management,’ the special core material arrived, but there

was a problem. It was not what we had contracted

for: the material was a three-layer board with the

core oriented at right angles to the face orientation.

A hurried test indicated that in other respects the

core was acceptable. There was no time to reorder if

we were to meet the deadline for the EER-II framing.

So we accepted the order and used it. This was a

wise decision.

Just as we started to fabricate the 2 by 4 truss

lumber, we were asked to furnish some additional

truss lumber for a two-car garage that had been

added to the project. All the core material available

from the original order was earmarked for necessary

research projects. We ordered some special phenolicbonded particleboard 7/8-inch thick with random

orientation that otherwise met our specifications for

internal bond and MOE. This material was used for

the garage truss lumber.

19
The deadline was met, and we loaded all of the

composite framing on an open flat-bed trailer for

delivery to the truss fabricator and the building site.

As the truck pulled away from the lab, it started to

rain, There were no tarps covering the load, but we

were not worried. This material had passed all of our

durability tests. Murphy’s Law applied in this

situation-disaster. A week later we received a call

from the truss fabricator. All of the garage trusses

were coming apart. The truss lumber was splitting

right throught the middle. What were we going to do

about it?

We found that the garage trusses made with the

random core material were splitting and coming

apart. The trusses made with the oriented core material

were fine. We needed to find out why, so we carefully

tested the physical and mechanical properties of the

two core materials. Every test recommended in ASTM

D-1037 was performed on both core materials plus

the I-l/Binch core used in the joists. There was

very little difference in the test results between the

particleboards except for thickness swell after a

24-hour water soak. The oriented core swelled about

5 percent; the thick core swelled about 10 percent;

and the random core swelled almost 30 percent. We

checked some other particleboards for thickness

swell. In every case where the thickness swell after a

24-hour water soak exceeded 15 percent, we were

able to reproduce the pattern of failure that had first

been observed in the garage trusses for the EER-II

project. Thickness swell became a major factor in

the specifications for the core material for composite

structural lumber.

Oriented-Core Performance

We also checked the performance of truss plates

in the oriented particleboard. To our surprise, the

lateral-load strength values for the particleboard

were high enough for effective use in trusses. Another

surprise was the low linear expansion (less than 0.5

percent) for the three-layer oriented particleboard

core. We assumed that low linear expansion was

due to the cross-oriented core layer. We also

contracted with the same producer for some fully

oriented flakeboard for core material; some 3/4-inch

thick for lamination into l-l/e-inch stock and some

7/8-inch stock for composite truss lumber.

The fully oriented core material was a real surprise.

To begin with, the linear expansion across machine

direction was about 0.3 percent after a 24-hour water

soak. Thickness swelling was about 5 percent. MOE

of particleboard is usually measured on a panel with

the smooth surfaces top and bottom. The MOE of

the flakeboard normal to panel surfaces (as a beam

with the cut edges top and bottom) averaged about

1.2 million PSI with an MOR of over 6,000 PSI. The

tension and compression values were also quite

high. There was about a 3 to 1 differential in MOE

parallel to and across machine direction. Thus, the

MOE of the oriented flakeboard across machine

direction was about the same as the MOE for random

oriented flakeboard. The lateral load resistance of

truss plates installed in the fully oriented core material

was only 10 percent less than for the same plates

installed in southern pine framing.

Actually, the fully oriented core material was a

fully structural product as it was, without any veneer

installed either on the edges or on the faces. This

was a remarkable development. One problem surfaced. Since the core material was so dimensionally

stable, when veneer was installed on members wider

than 3.5 inches there was a serious problem with

the faces swelling so much that the member took on

a barrel shape. The problem was severe enough to

cause splitting of the core at the center of the member

after a couple of cycles of wetting and drying.

No further development work was done on the

fully oriented flakeboard as a structural material

because funding for the RWU was withdrawn and

the project was terminated in 1986.

Solid Accomplishments

Research on composite framing for studs started

in 1974. Standards for the evaluation of performance

characteristics of stud framing were developed, and

a fully satisfactory composite stud was developed by

1975. Research on composite joists culminated in a

fully satisfactory joist in 1978. Satisfactory composite

truss lumber was produced by 1982. An experimental

core material for composite truss lumber was found

to be a fully structural material in its own right in

1985.

Economics of resource availability, market demand, and production feasibility were considered at

every stage of the research. The RWU achieved all

of its research objectives and goals well within the

projected timeframes.

The RWU was terminated September 30, 1986. It

was decided that further research and development

of composite structural products would best be

accomplished by industry.

20
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21
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22
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23

McAlister, Robert H.

1999. The research and development of COM-PLY lumber. Gen.Tech. Rep. SE-53.

Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest

Experiment Station. 23 pp.

Between 1974 and 1986, a Southeastern Station Research Work Unit developed standards

for composite studs, joists, and truss lumber and manufactured and demonstrated the

materials. Economic feasibility was considered in every stage of research. Further

development is left to industry.

Keywords: Construction lumber, composite lumber, truss lumber, joists, studs, performance

standards.

McAlister, Robert H.

1989. The research and development of COM-PLY lumber. GenTech. Rep. SE-53.

Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest

Experiment Station. 23 pp.

Between 1974 and 1996, a Southeastern Station Research Work Unit developed standards

for composite studs, joists, and truss lumber and manufactured and demonstrated the

materials. Economic feasibility was considered in every stage of research. Further

development is leff to industry.

Keywords: Construction lumber, composite lumber, truss lumber, joists, studs, performance

standards.
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Agriculture, is dedicated to the principle of

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