Efficient Utilization of

Red Maple Lumber in

Glued-Laminated

Timber Beams

John J. Janowiak

Harvey B. Manbeck

Roland Hernandez

Russell C. Moody

Paul R. Blankenhorn

Peter Labosky

United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

Research

Paper

FPL–RP–541
Abstract

The feasibility of utilizing cant-sawn hardwood lumber, which

would not usually be desired for furniture manufacture, was studied

for the manufacture of structural glued-laminated (glulam) timber.

Two red maple beam combinations were evaluated: (1) a glulam

combination designed with E-rated lumber in 25 percent of the

outer laminations (top and bottom) and No. 3 grade lumber in

50 percent of the center laminations and (2) a wide-width glulam

combination with laminations made from nominal 2- by 4- and

2- by 6-in. No. 2 grade lumber laid edge-to-edge having staggered end joints (termed 2 by 4/2 by 6 glulam combination).

Test results of 42 red maple glulam beams showed that it was

feasible to develop structural glulam timber from cant-sawn lumber. The glulam combinations made from E-rated lumber exceeded

the target design bending stress of 2,400 lb/in2

 and met the target modulus of elasticity (MOE) of 1.8 × 106 lb/in2

. In addition,

the 2 by 4/2 by 6 glulam combination exceeded published design

stresses for vertically laminated bending strength, MOE in both

the horizontally and vertically laminated orientations, and horizontal shear stress in the vertically laminated orientation. Based

on the results of the 2 by 4/2 by 6 glulam combination, it was

determined that edge gluing the laminations to form wide-width

lumber is not required to achieve targeted strength and stiffness

levels.

Data analysis showed that ASTM D3737 procedures developed

for softwood species accurately predict beam stiffness and provide conservative bending and horizontal shear strength

estimates for red maple glulam beams. Also, it was shown that

results from ASTM D143 shear-block tests could be used to

accurately predict horizontal shear strength of 2 by 4 and 2 by 6

red maple glulam beams.

Keywords: Red maple, hardwood, glulam, E-rated lumber, log

cants

September 1995

Janowiak, John J.; Manbeck, Harvey B.; Hernandez, Roland; Moody,

Russell C.; Blankenhorn, Paul R.; Labosky, Peter. 1995. Efficient utilization

of red maple lumber in glued-laminated timber beams. Res. Pap. FPL–RP–

541. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory. 23 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.

The United States Department of Agriculture (USDA) prohibits discrimination in its programs on the basis of race, color, national origin, sex,

religion, age, disability, political beliefs, and marital or familial status.

Persons with disabilities who require alternative means of communication

of program information (braille, large print, audiotape, etc.) should contact

the USDA Office of Communications at (202) 720–2791. To file a complaint, write the Secretary of Agriculture, U.S. Department of Agriculture,

Washington, DC 20250, or call (202) 720–7327 (voice), or (202) 720–1127

(TTD). USDA is an equal employment opportunity employer.

Acknowledgment

We express sincere gratitude to Bradford Forest Products, Inc. in

Bradford, Pennsylvania, for preparing essential cant-sawn lumber supplies and Unadilla Laminated Products in Unadilla, New

York, for fabrication of the test beams. In addition, special

thanks to the Engineering Mechanics Laboratory technicians

of the USDA Forest Service, Forest Products Laboratory, in

Madison, Wisconsin, for their valuable assistance in the beam

testing.

The research reported herein was sponsored and funded by the

Pennsylvania Department of Transportation, Office of Special

Studies (Project No. SS−043), and the Pennsylvania Agriculture

Experiment Station. The project was conducted jointly between

the Pennsylvania State University, and the USDA Forest Service,

Forest Products Laboratory.

Contents

 Page

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

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

Objectives and Scope ...................................................2

Experimental Design....................................................2

Material and Methods...................................................4

Evaluation Results.......................................................8

Analysis of Results......................................................9

Conclusions .............................................................14

References................................................................14

Appendix ARelative Quality Estimates

of Red Maple Lumber.................................................15

Appendix BDestructive Tests...................................16

Appendix CGlulam Beam Failure Maps

 and Lumber Properties...........................................20

Appendix DASTM Procedures .................................23
John J. Janowiak, Associate Professor of Wood Products

Harvey B. Manbeck, Professor of Agricultural Engineering

The Pennsylvania State University

University Park, Pennsylvania

Roland Hernandez, Research General Engineer

Russell C. Moody, Supervisory Research General Engineer

USDA Forest Service, Forest Products Laboratory

Madison, Wisconsin

Paul R. Blankenhorn, Professor of Wood Technology

Peter Labosky, Professor of Wood Science and Technology

The Pennsylvania State University

University Park, Pennsylvania

Introduction

Several recent publications have presented experimental

results on the mechanical performance of hardwood gluedlaminated (glulam) timbers (Manbeck and others 1993;

Moody and others 1993; Shedlauskas and others 1994). These

glulam studies are related to broader research efforts in the

development of timber bridge systems. Glulam is a vital

element for many proposed timber bridge designs. One key

issue in bridge research is the use of local, underutilized

forest resources. Published performance results of red maple,

yellow poplar, and red oak support the feasibility that

hardwood glulam timbers are well-suited for bridge applications. These hardwood species are abundant, with significant

saw-timber volume in Pennsylvania and numerous other

states where annual growth accumulations exceed harvest.

The project reported here was initiated to examine the use of

low-grade, small-dimension red maple obtained from cantsawn lumber for glulam timber manufacture. Cant refers to

the remaining log heart or inner-log portion after grade

sawing removes the higher quality, outer-zone material for

appearance-type lumber.

Background

Design values of 2,400 lb/in2 bending stress and 1.8 × 106

lb/in2 stiffness (modulus of elasticity (MOE)) were found to

be feasible for red maple, yellow poplar, and red oak glulam

(Manbeck and others 1993; Moody and others 1993; Shedlauskas and others 1994). (See Table 1 for SI conversion

factors.) These cited studies intended to improve upon hardwood glulam performance with efficient beam combinations

using E-rated outer and No. 2 visually-graded lumber inner

laminations. These studies served to verify the applicability

of ASTM D3737 (ASTM 1993) analytical procedures to

predict hardwood glulam design performance on the basis of

lumber properties. Also, the studies defined appropriate volume effect coefficients for flexural strength adjustment for red

maple, yellow poplar, and red oak glulam timber products.

Results from these studies have been accepted by the American Institute for Timber Construction (AITC), and hardwood

glulam combinations using E-rated lumber are being incorporated in the AITC 119 (AITC 1985) standard.

Efficient Utilization of

Red Maple Lumber in

Glued-Laminated Timber Beams

Table 1—SI conversion factors

English unit

Conversion

factor SI unit

foot (ft) 0.3048 meter (m)

inch (in.) 25.4 millimeter (mm)

pound (lb) 0.4535 kilogram (kg)

pound per square inch (lb/in2

) 6.894 pascal (Pa)
2

Other studies are also emerging to explore the yield recovery

and lumber properties of structural-graded hardwoods. Green

and McDonald (1993) investigated the mechanical properties

of red oak nominal 2- by 4-in. (2 by 4) lumber. Janowiak and

others (1992) reported on flexural properties and computed

design values for Select Structural and No. 2 red maple 2 by

4’s. Janowiak and others (1994) also reported on the compressive strength properties of red maple and northern red oak

glulam. McDonald and others (1993) conducted a study on

the conversion of red maple factory-grade logs for production

of structural 2 by 4’s. Study results indicated that hardwood

design property values may only be conservatively estimated

on the basis of clear wood computational procedures. Another

study is investigating joist and plank lumber grade yield from

railroad switch ties for five hardwood species (McDonald and

others [in press]), in an attempt to develop a structural lumber product that does not compete with hardwood sources

used by the furniture industry. Preliminary results with red

oak, hickory, yellow poplar, and red maple switch ties indicate yields of nominal 2- by 7-in. lumber to exceed 90 percent No. 3 & better lumber.

Railroad switch ties and log cants have significant potential

as a source for structural lumber. Hardwood sawmills frequently avoid processing inner-log portions because of inadequate appearance grade recovery. Hardwood cants sawn into

structural lumber would provide sawmills with an enhanced

opportunity for value-added production. The recovery concept

first obtains appearance-type lumber from high quality outerlog portions, then stress-graded dimension lumber from the

heart cant. Small 2- by 4- or 2- by 6-in. (2 by 6) nominal

cant-sawn lumber could be used for manufacture of hardwood

glulam timbers. Wide-width glulam timber products could be

fabricated by manufacturing laminations with two narrowwidth lumber specimens laid edge-to-edge. Using laminations

made from lumber placed edge-to-edge is an accepted practice

for glulam beam fabrication (ANSI 1992). More commonly,

this practice is reserved where glulam beam width exceeds

largest available dimension lumber. These two-member

laminations can include lumber pieces of either a glued or

unglued edge joint.

Several articles have reported on the mechanical properties of

edge-glued dimension lumber. Edge-glued Southern Pine

lumber was studied to develop a solution to projected shortages of wide-dimension construction lumber (McAlister

1973). Another study was conducted with Douglas-fir clear

wood that was edge-glued in various combinations with

structural No. 3 and L1, L2, and L3 lamination grades of

lumber (Johnson 1978). Both studies suggest that edge-toedge combinations can provide enhanced lumber products or

beams with increased mechanical performance. This is due to

the reduced influence of width effect in the laminating stock,

as a result of using two narrow-width pieces of lumber.

Objectives and Scope

No research has been reported that thoroughly evaluates the

mechanical performance of glulam products composed of

unglued two-member laminations. Design stresses for these

structural glulam timbers are established according to ASTM

D3737. This standard specifies for laminations that lumber

edge joints must be glued unless calculations or experimental

data provide verification of structural performance. In addition, no research has been reported on glulam timber made

from two-member laminations when tested in the vertically

laminated orientation (loads applied parallel to the wide face

of the laminations).

In our study reported here, two objectives were addressed to

examine several aspects of red maple glulam product performance using low grade and small nominal-sized lumber

processed from resawn cants. The first objective was to

develop a glulam beam configuration using No. 3 grade lumber for 50 percent of the inner laminations that would achieve

a design bending stress of 2,400 lb/in2 and a design bending

MOE of 1.8 × 106 lb/in2 (24F–1.8E). Fifteen 24F–1.8E red

maple glulam beams were manufactured for evaluation of

bending strength and stiffness. The second objective focused

on determining bending strength, shear strength, and bending

stiffness properties of glulam beams made with No. 2 grade

laminations having unglued nominal 2 by 4’s and 2 by 6’s

laid edge-to-edge. These beams were evaluated with loads

applied parallel to the wide face of the laminations (y–y beam

axis). In addition, fifteen 2 by 4 and 2 by 6 glulam beams

made with No. 2 visually-graded red maple lumber were

manufactured for evaluation of flexural properties with load

applied perpendicular to the wide face of the laminations

(x–x beam axis). An additional set of twelve 2 by 4 and

2 by 6 glulam beams were fabricated for evaluation of beam

shear strength in the y–y beam axis.

Experimental Design

Prior to procuring materials and manufacturing the glulam

beam combinations for our study, it was necessary to determine the feasibility of achieving the targeted design stresses.

Research by Manbeck and others (1993), Moody and others

(1993), and Shedlauskas and others (1994) showed that glulam combinations made from red maple, yellow poplar, and

red oak lumber, respectively, could achieve design stresses of

2,400 lb/in2 in bending strength and 1.8 × 106 lb/in2 in

bending stiffness. Based on these research studies, E-rated

hardwood lumber properties were established for ASTM

D3737 analytical procedures. Results of these previous

studies provided estimates of the lumber properties (Table 2).
3

Glulam With No. 3 Core Laminations

Efficient, red-maple glulam combinations studied by Manbeck and others (1993) were recently proposed for inclusion

in the industry standard for hardwood glulam, AITC 119.

The major differences between the Manbeck and others study

and our study presented here are that all lumber for our study

was obtained from sawn cants and No. 3 grade lumber was

targeted for the core laminating stock. Past research has also

shown that ASTM D3737 procedures adequately predict the

performance of hardwood glulam. The analysis conducted for

this study was carried out to determine if targeted glulam

design stresses (24F–1.8E) were technically feasible while

utilizing the low grade core material.

Based on ASTM D3737 analytical procedures and the lumber

property information in Table 2, the experimental 24F–1.8E

beam configuration with No. 3 beam core laminations was

developed (Fig. 1). The glulam beams were composed of

outer zones of E-rated lumber and a core zone of No. 3 visually-graded lumber. Allowable edge-knot size of the E-rated

lumber for the outermost 10 percent of the tension laminations was limited to one-sixth (1/6) the area of the cross section. Edge-knot size in the outer 10 percent of the compression laminations was restricted to one-third (1/3) the area of

the cross section. Bending stiffness for these two outermost

tension and compression zones required E-rated lumber meeting an average MOE of 2.0 × 106

 lb/in2. Edge-knot size in

the next inner 15 percent of the tension and compression

laminations was restricted to one-third (1/3) the area of the

cross section. Bending stiffness for the two next inner zones

required average lumber MOE values of 1.8 × 106 lb/in2. In

addition, ASTM D3737 procedures require that 5 percent of

the outermost tension laminations be replaced with a special

tension grade lumber meeting the criteria summarized in

Table 3.

2 by 4 and 2 by 6 Wide-Width

Glulam Beams

This research targeted the evaluation of the beams for bending

strength in the y–y beam axis and horizontal shear strength

in the same y–y beam axis. Glulam timber beams with

laminations made with nominal 2 by 4’s and 2 by 6’s placed

edge-to-edge are referred to as 2 by 4/2 by 6 beams throughout the remainder of this report.

The dimensions of the 2 by 4/2 by 6 beams in our study

were designed with a staggered arrangement of nominal 2 by

4’s and 2 by 6’s (Fig. 1), having a total of five laminations.

Visually-graded No. 2 red maple lumber was used throughout

the layup, and the edge interface between the 2 by 4 and

2 by 6 plies was not glued. In the proposed AITC 119 standard, vertically laminated red maple glulam beams with four

or more laminations of No. 2 grade lumber have assigned

design bending stresses in the y–y beam axis (Fby) of

1,450 lb/in2 and design horizontal shear in the y–y beam axis

(Fvy) of 160 lb/in2. When laminations are made using edgeto-edge lumber, Fvy values are reduced to 65 lb/in2

.

Table 2—Estimated property values of red maple

lumber for use in ASTM D 3737 procedures

Lamination

grade

MOE

(×106

 lb/in2)

x a

(%)

x + hb

(%) SRmin

c

Bending

stress

index

(lb/in2

)

2.0-1/6 2.0 3.0 27.0 0.70 3,250

2.0-1/3 2.0 5.0 35.0 0.60 3,250

1.8-1/3 1.8 5.0 35.0 0.60 2,750

No. 2 1.5 8.0 42.0 0.54 2,470

No. 3 1.4 10.0 50.0 0.39 2,470

a x = average of sum of all knot sizes within each

1-ft length, taken at 2-in. intervals.

 b x + h = 99.5 percentile knot size (ASTM 1993). c

SRmin = minimum bending strength ratio.

All No. 2 grade

Loading in y-y axis

2x6

2x4

Loading in x-x axis

Actual Design

(2)

(1)

(6)

(1)

(2)

2.0-1/3

1.8-1/3

No. 3

1.8-1/3

2.0-1/6

TL

2.0-1/3

1.8-1/3

No. 3

1.8-1/3

2.0-1/6

No. 2













Figure 1—Illustration of red maple glulam:

(left) 24F–1.8E combination and (right)

2 by 4/2 by 6 combination.

Table 3—Maximum allowable tension

lamination criteria for 24F–1.8E glulam

beam combination

Characteristic

Maximum

allowablea

Edge knot + grain deviation 30 percent

Center knot + grain deviation 40 percent

Slope of grain 1:16

a

Knots plus grain deviations are given in percentages of cross section per ASTM D3737 (1993).
4

Material and Methods

Lumber Manufacture

and Grade Yield

Lumber for manufacture of the 24F–1.8E and 2 by 4/2 by 6

glulam combinations was processed from residual red maple

log cants. Red maple (Acer rubrum) logs were harvested from

several northcentral Pennsylvania sites. Logs were first processed with primary breakdown to recover appearance grade

hardwood lumber. Primary breakdown included sawing of

appearance-type lumber to recovery down to a No. 3A Common NHLA (National Hardwood Lumber Association) grade

face (NHLA 1992). After appearance material was removed,

the log hearts (approximate 6-in. to a minimum 4-1/2 in.

dimension cants) were processed through a secondary bandmill resaw operation. Cants were sawn to a heavy 6/4 (final

dressed thickness will equal 1.5 in.) hardwood lumber thickness tolerance. Immediately after sawing, the rough lumber

was tallied to monitor the amount of 2 by 4 and 2 by 6

material available for experimental beam fabrication and

graded green according to NELMA (Northeastern Lumber

Manufacturers Association) grading rules to estimate structural grade yield.

Initial green lumber tally indicated a structural grade recovery

as follows: 5.8 percent Select Structural (SS), 24.8 percent

No. 1, 40.9 percent No. 2, 19.8 percent No. 3, and 8.7 percent below grade material. Collectively, No. 3 & better lumber equaled a 91.3 percent recovery for the resawn cants.

Recovery coincided closely to the grade yield results for structural lumber processed from sawn railroad switch ties. A

yield of 30.6 percent for SS and No. 1 lumber was greater

than anticipated. The No. 1 & better recovery and relatively

low percentage of below grade lumber (cull) were undoubtedly influenced by cant selection.

Grading, Sorting, and

Stiffness Evaluation

The lumber was kiln dried to approximately 12-percent moisture content. After drying, the red maple lumber was processed through a surface planer. Planer operation was set-up

for a 1.49-in. thickness for dressing of lumber surfaces.

Lumber shrinkage dictated this dressed dimension to minimize planer skip. Dressed lumber was then transported to the

cooperating glulam manufacturing facility. Lumber was

sorted again at the laminating plant to account for lumber

degradation after the kiln-drying process. Significant amounts

of No. 3 green grade were removed from the initial lumber

population as a result of drying-related defects of bow, twist,

and excessive end splits, which fell outside of the No. 3 grade

limitations. Less severe end-split defects of all lumber were

removed. The four lumber grades were visually sorted into

grades meeting tension lamination criteria, one-sixth (1/6)

and one-third (1/3) edge-knot size restrictions, as well as

No. 3 lumber. The fractions, 1/6 and 1/3, refer to the amount

of cross-sectional area of the lumber that is occupied by a

knot. The remaining lumber not meeting the stated edge-knot

requirements was assigned to the No. 3 visual grade.

Additional sorting was conducted to separate supplies of

nominal 2 by 4 and 2 by 6 No. 2 lumber for fabrication

of the 2 by 4/2 by 6 glulam beams.

When the lumber grades were visually sorted, stiffness properties were determined with commercial transverse vibration

equipment (Metriguard 1993). Each piece of lumber was

marked with an identification number, and the corresponding

stiffness was recorded. A small sample of lumber was tested

for flatwise MOE as specified in AITC T116 (AITC 1992) to

establish a regression relationship between dynamic and static

lumber MOE (Fig. 2). The difference between dynamic MOE

and static MOE was found to be greater than 5 percent; this

was due to inconsistent calibration of the test equipment.

Thus, for subsequent analyses with the ASTM D3737

procedures, dynamic MOE values were adjusted using the

regression relationship. Sorting of the lumber to achieve the

targeted MOE levels (Table 2) followed specifications published in AITC 117–Manufacturing for E-rated laminating

lumber (AITC 1993) (Table 4). Special tension lamination

material meeting the criteria in Table 3 was selected from the

available E-rated 2.0–1/6 lumber.

Knot Properties

After the required amounts of lumber were sorted, knot property data were measured for most of the grades. Knot data

were collected for all specimens of special tension lamination

material, all 2.0–1/6 pieces, and randomly selected samples

of the No. 2 and No. 3 lumber. Additional knot data were

collected for the No. 2 grade 2 by 4 lumber intended for the

3.0

2.5

2.0

1.5

1.0 1.5 2.0 2.5 3.0

Dynamic MOE (x106 lb/in2)

Static MOE (x106 lb/in2)

n = 74

Static MOE = 0.103 + 0.890

 (dynamic MOE)

r

2 = 0.85

Figure 2—Relationship between static and

dynamic MOE.
5

2 by 4/2 by 6 beam fabrication. As a result of the time constraints, knot data for the 1/3 edge-knot grades were not gathered (2.0–1/3 and 1.8–1/3). Knot data were later analyzed

according to procedures in USDA Technical Bulletin 1069

(Freas and Selbo 1954). Later analyses requiring knot data

information for the 1/3 edge-knot grades would use that

reported by Manbeck and others (1993).

Glulam Beam Manufacture

24F–1.8E Glulam Beams

The 12-lamination 24F–1.8E red maple glulam beams of

30-ft length were manufactured from nominal 2 by 6’s. As a

result of greater than anticipated drying losses of No. 3 grade

lumber, approximately half the core laminations had to be

replaced with No. 2 grade lumber. The No. 3 grade laminations were placed on the tension side of the core, and No. 2

grade laminations were placed in the compression side of the

core (Fig. 1). Thus, ultimate glulam beam failures occurring

in the core laminations would likely be caused by the

strength of the No. 3 grade lumber. Based on a simple transformed section analysis, it was determined that the three

No. 2 grade core laminations would account for approximately 6.2 percent of the glulam beam stiffness. Two additional No. 3 core laminations were substituted into glulam

beams RM6-12, RM6-13, and RM6-14. For later analysis,

all E-rated laminations and the outer-core laminations were

identified during dry layup to develop beam maps of lumber

stiffness properties. A total of 15 glulam beams were manufactured based on the available supplies of lumber having

proper grade characteristics.

Because the performance of the tension lamination finger

joints are a critical part of glulam beam performance, fingerjoint specimens were gathered during beam manufacture to

determine their ultimate tensile strength. Finger joints used

in this study were vertically oriented (fingers visible on the

wide face of the lumber). Because of the low-quality cantsawn lumber resource, adequate sample sizes of lumber

specimens meeting the special tension lamination grade

requirements for both glulam beam and finger-joint specimen

manufacture were difficult to obtain. Thus, beam manufacture

was given greater priority for allocation of available tension

lamination material compared with finger-joint sampling.

After an initial selection of tension lamination quality material from the sorted 2.0–1/6 lumber, it was apparent that

adequate quantities of tension lamination material would not

be available for finger-joint sampling. Thus, a second selection process was carried out to gather those pieces of lumber

that had grade characteristics at or near the allowable tension

lamination grade requirements. Thus, those lumber specimens gathered for beam manufacture had a range of qualities

meeting the tension lamination grade requirements, and the

grade characteristics of the finger-joint specimens were

heavily weighted toward the maximum characteristics allowed

in the grade.

2 by 4/2 by 6 Glulam Beams

The 2 by 4/2 by 6 glulam beams were manufactured with

five laminations that resulted in approximately a 6.5-in.

depth, 8-in. width, and 13.3-ft length. Procedural steps

followed for manufacture of 2 by 4/2 by 6 glulam beams

were almost identical to conventional lumber lamination

procedures. One major difference was that lumber widths were

staggered in adjacent beam lamination layers (Fig. 1) during

final layup. No attempt was made to bond the lumber on the

longitudinal edge-to-edge joint. Some edge-to-edge joints

became partially bonded as adhesive flowed into a joint as a

result of the application of clamp pressure during beam assembly. Edge-joint quality varied from having tight-edge

surface contact to open gaps observed along the lamination

edge length. Figure 3 shows a cross section of a 2 by 4/2

by 6 glulam beam to illustrate the variable nature of edgejoint gaps. The location of lumber identification numbers of

each 2 by 4 and 2 by 6 specimen was mapped so that MOE

properties of the glulam beam could be later estimated based

on the MOE properties of the constituent lumber. Fifteen

13.3-ft-long 2 by 4/2 by 6 beams were fabricated for evaluation of bending strength and twelve 7.5-ft-long 2 by 4/2 by 6

beams were fabricated for evaluation of horizontal shear

strength.

Modifications to Manufacturing Procedures

In previous work (Manbeck and others 1993), portions of

tested red maple glulam beams exhibited shallow wood failure at the gluelines that were caused by an inadequate gluing

surface. The rough surfaces of the red maple lumber were

caused by processing of the high-density lumber through

surface planers operating at speeds that were adequate for

Table 4—Target MOE values and sorting scheme

Lamination

 grade Sorting and grading criteria

2.0–1/6 MOE average between 2.0 to 2.1 × 106

 lb/in2

No piece < 1.60 × 106 lb/in2

5th percentile of at least 1.67 × 106 lb/in2

No piece > 2.4 × 106 lb/in2

Edge knot limited to 1/6 cross section

2.0–1/3 MOE restrictions same as for 2.0–1/6 grade

Edge knot limited to 1/3 cross section

1.8–1/3 MOE average between 1.8 to 1.9 × 106

 lb/in2

No piece < 1.40 × 106 lb/in2

5th percentile of at least 1.45 × 106 lb/in2

No piece > 2.2 × 106 lb/in2

Edge knot limited to 1/3 cross section
6

softwoods. To produce adequate bonding surfaces, lumber feed

rates into the surface planer were reduced and clamping

pressures applied during glulam beam curing were increased.

The AITC T103 (1992) procedures were followed to develop

a relationship between torque and tension bolt force.

Preparation for Testing

After manufacture, the 24F–1.8E glulam beams were transported to the testing facilities. Beams were visually inspected

to ensure conformance to ANSI A190.1 (1992) for glulam

products. The inspection was also conducted to determine

relative visual qualities of the tension lamination in the

midlength region that would be subjected to greater than

85 percent of maximum bending moment during test. The

midlength region was rated with a system developed on the

basis of maximum allowable strength-reducing characteristics

(Table 3). The relative rating system to assign lamination

quality is detailed in Table 5.

Evaluation Procedures

Testing equipment and procedures for evaluating the glulam

beams and the end-jointed lumber specimens followed criteria

in ASTM D198 (1993a).

24F–1.8E Glulam Beams

The glulam beams were destructively evaluated using ASTM

D198 procedures. Loading configuration included a 28-ft

reaction support span with a 6-ft load span as shown in

Figure 4. Long-span deflection was measured at the neutral

axis over the unsupported beam length. Shear-free deflection

was also measured over a 5-ft span between the loading

points. Physical properties of weight, moisture content, and

dimensions were measured on individual beam specimens.

Measurements were recorded for the failure load and time-tofailure tests. Efforts were also made to take notes on failure

type with sketches of beam failure pattern. Moisture content

was determined after failure using a resistance-type moisture

meter with measurements on each lamination near mid-span

location. Beam weights were measured prior to testing on a

mobile scale to an approximate 10-lb accuracy. Dimensions

of width and depth were taken at beam load positions. During

loading, full-span deflection readings were recorded at specified incremental loads to compute beam stiffness from a

regressed fit of load-deflection data up to design load.

Finger-Jointed Lumber

The finger-jointed specimens were evaluated to determine

their ultimate joint tensile strength. Only 15 test specimens

had been prepared for tensile strength evaluation because of

the limited supplies of special tension lamination grade material. Test specimens were face- and surface-planed prior to

testing to similar dimensions as the laminations used for

beam manufacture. Prior to test, each specimen was evaluated

with an E-computer to obtain a dynamic MOE measurement.

Specimens were approximately 8-ft long with the finger joint

located near midlength. Tests included a 30-in. gage length

centered between machine grips, with increasing tensile load

applied until failure. Loading rate was calibrated to achieve an

approximate 5- to 10-min time to failure. This loading is

longer than the 3 to 5 min recommended by AITC T119 for

daily quality control testing. The 5 to 10 min used in our

study coincided with the failure times targeted for the full-size

glulam beam tests, which followed ASTM D198 procedures.

Upon test completion, observed fracture was mapped for each

finger-joint specimen. For specimen mapping, the location

of the finger joint between the tension machine grips was

defined as zero (0), and the propagation of failure was mapped

from a positive (+) to negative (−) distance with respect to

the finger joint. If the 0 location was absent from a mapped

failure description, then failure did not occur at a finger joint

and the test result was not considered in the finger-joint

analysis. After tension testing, small wooden sections from

either side of the finger joint were removed for specific

gravity determination.

Figure 3—Cross section of 2 by 4/2 by 6

glulam combination, showing variation in

gaps between edge joints.
7

Table 5—Relative rating system for tension lamination quality of 24F–1.8E glulam beams

ASTM D3737 Lamination quality

Characteristic

allowable

 value Low Medium High

Edge Knot + Grain Deviation 30 percent >20 percent 10−20 percent 10 percent

Center Knot + Grain Deviation 40 percent >20 percent 15−30 percent <15 percent

Slope of Grain 1:16 <1:18 1:18−:20 >1:20

MOE (x106

 lb/in2) 2.0E (avg.) <1.75 w/chara <1.75 and clear —

a

w/char designates lumber with characteristics. For example, if a board has an MOE of <1.7E

 and a edge-knot, center-knot, or slope-of-grain characteristic, it is classified as low quality.

16.25 in. 16.25 in.

32.5 in. 32.5 in.

(b)

Load (a)

span

Support span

Glulam

combination

Support

span (ft)

Load

span (ft)

24F-1.8E 28.0

12.5

6.00

2x4/2x6 4.17

Figure 4—Loading configurations for (a) bending and (b) shear tests of red maple glulam beams.
8

2 by 4/2 by 6 Glulam Beams

Flexural tests followed ASTM D198 procedures for all 2 by

4/2 by 6 glulam beam specimens. A computerized data

acquisition system was used to monitor load-deflection

response. Loading rate for maximum load was adjusted for a

5- to 10-min time-to-failure test duration. Deflection measurements were taken using a linear variable differential transformer (LVDT) on a yoke affixed to the neutral axis of the

specimen. The MOE values were computed from a linear

regression analysis of load-deflection data up to design load.

The 2 by 4/2 by 6 specimens of 80-in. (7.5-ft) length were

also processed from the 2 by 4/2 by 6 glulam materials to

characterize beam shear strength (τ). Beam shear strength

evaluation was conducted utilizing a five-point loading

scheme recommended by Soltis and Rammer (1994). The test

apparatus consists of three reaction supports, located at either

beam end and midspan, and two loading points, each located

equidistant from midspan (Fig. 4). Specimen length was

10 times the member depth, with span between the reaction

supports equal to 5 times the depth. Concentrated loads were

applied through bearing plates to minimize compressive failure. Test speed was selected so that shear failures would occur

between 5 and 10 min after load application. After failure,

beam shear failure zones were sketched and moisture content

determined with a resistance-type meter.

The ASTM D143 (1993b) shear-block specimens were fabricated using wood samples obtained from locations adjacent to

the shear failure zones of the 2 by 4/2 by 6 glulam beams.

An evaluation could include one or more observations of

shear strength relative to the multiple lumber piece construction. Individual observations were averaged as a measurement

of ASTM D143 shear strength for each failed 2 by 4/2 by 6

lamination. Two data sets were developed with one set tested

at ambient or unconditioned moisture content and the other

after conditioning to constant weight at 12 percent equilibrium moisture content. A numerical code system was

developed to describe location of each solid-wood shear

specimen relative to its position within a particular 2 by

4/2 by 6 glulam beam. For example, a sample observation

removed from the third lamination (3) of the red maple 2 by

4/2 by 6 beam having the identification number RMC6-1

(6-1) would have a shear-block identification number of

6–1–3.

Evaluation Results

Glulam Manufacture

To determine if the targeted laminating lumber MOE criteria

in Table 2 were achieved, the glulam beam maps compiled

during beam manufacture were analyzed to determine the final

arrangement of the sorted lumber. Table 6 gives a statistical

summary of MOE measurements of those lumber specimens

used in the fabricated beams for both the 24F–1.8E and 2 by

4/2 by 6 glulam combinations. Note that the special tension

lamination and all the E-rated grades (2.0–1/6, 2.0–1/3,

1.8–1/3) met or slightly exceeded the targeted average MOE

values. Both visual grades (No. 2 and No. 3) greatly exceeded

the assumed property values in Table 2.

The measured knot properties on the sorted lumber grades

were also analyzed to determine knot size statistics. Table 7

includes a statistical summary of the knot sizes observed in

each grade for lumber used in both the 24F–1.8E and 2 by

4/2 by 6 glulam beam combinations. A comparison of the

results in Table 7 to knot properties observed by Manbeck

and others (1993) for similar grades and widths of red maple

lumber was conducted. We observed that lumber grades sorted

in our study resulted in significantly larger knots when compared with those of Manbeck and others (1993). This could

Table 6—MOE values of sorted laminating lumber

in glulam beams

Lumber

width

(in.)

Lumber

grade

Number

of pieces

Average

MOE

(×106

 lb/in2)

COV

 (%)

2 by 6 TLa

2.0–1/6

2.0–1/3

1.8–1/3

No. 2

No. 3

55

56

113

114

160

25

2.15

2.05

2.02

1.79

1.84

1.68

7.8

9.7

9.4

9.1

10.9

11.4

2 by 4 No. 2 161 1.82 15.3

a

TL = tension lamination.

Table 7—Knot sizes of sorted laminating lumber

Nominal

lumber

size Lumber grade

Lineal

footage

(ft)

x a

(%)

x + hb

(%)

2 by 6 TLc

 2.0–1/6

TL and

 2.0–1/6 combined

No. 2

No. 3

212

282

494

221

221

0.5

1.5

0.9

2.3

5.2

15.0

34.8

29.3

27.4

51.5

2 by 4 No. 2 200 3.0 47.5

2 by 4/ 2 by

6 combined

No. 2 421 2.7 36.4

a x = average of sum of all knot sizes within each 1-ft

length, taken at 2-in. intervals.

 b x + h = 99.5 percentile knot size (ASTM 1993). c

TL = tension lamination.
9

be a result of the difference in lumber resource, where the

lumber from our study was sawn from center log cants.

Relative qualities of the tension laminations for the

24F–1.8E glulam beams were also determined based on the

criteria in Table 5. The tension lamination properties observed for each beam are summarized in Appendix A, Table

A1. Results of this inspection are given in Table 8. Note the

nearly equal number of low and high quality glulam beams,

based on the visual characteristics of their respective tension

laminations.

24F–1.8E Glulam Beams

During testing, beams emitted fiber fracture sounds before

reaching ultimate failure load. Some beams were observed

with localized compressive wrinkling between the load points

prior to ultimate failure on the tension side. Most failures

were attributed to finger joints, and other beams failed because of a combination of finger joint and other intrinsic

strength-controlling characteristics. Failure occurred throughout three E-rated laminations and into the No. 3 interlaminations (Fig. 5). A tally of the estimated causes of failure is

provided in Table 9. In comparison to the Manbeck and others red maple glulam study, improved glueline bonding was

indicated in our study by greater percentages of wood failure

and deeper adhesive penetration. Glueline-type failures were

not observed and tension-side beam rupture was commonly a

failure mechanism with fracture propagation through several

consecutive laminations. Destructive test evaluation results

on 24F–1.8E beam strength and stiffness are summarized in

Table 10. Results of individual beam tests are provided in

Appendix B, Table B1, and illustrations of individual glulam

beam failures are provided in Appendix C. All calculations

of glulam beam MOR include the dead weight of the beams.

Finger-Jointed Lumber

Results on tensile strength, moisture content, and specific

gravity for the finger-jointed special tension lamination

specimens are given in Table 11. Individual results for the

end-joint tests and other collected data are presented in

Appendix B, Table B2.

2 by 4/2 by 6 Combination

Glulam Beams

For bending tests of the 2 by 4/2 by 6 glulam beams, the

majority of failures involved a strength-reducing characteristic, such as knots, slope of grain, or grain deviation. The use

of the edge-to-edge laminations did not appear to affect the

bending strength results. Summary results from the flexural

testing are presented in Table 10. Individual test observations

for the 2 by 4/2 by 6 glulam beam flexural tests are included

in Appendix B, Table B3.

For the horizontal shear tests of the 2 by 4/2 by 6 glulam

beams, the first audible sound of failure was emitted at ultimate load; then the load-carrying capacity was observed to

decrease. Because no catastrophic failure was observed during

this loading sequence, cross sections of each of the 12 beams

were cut at the location of failure, and the propagation of

horizontal shear failure was observed. The descriptions of

each failure were mapped and are illustrated in Appendix C.

Summary test results for beam horizontal shear are presented

in Table 12. Individual test observations for the combination

beam shear tests are given in Appendix B, Table B4. The

results of the ASTM D143 shear-blocks that correspond to

the glulam beams are given in Table 13. Individual test observations from the ASTM D143 shear-block tests are collectively presented in Appendix B, Table B5.

Analysis of Results

The analysis conducted in this section assumes the lognormal

distribution for strength property characterization,

recommended by ASTM D3737. Analysis of glulam MOE,

moisture content, and specific gravity were conducted

assuming the normal distribution.

Table 8—Relative quality of tension

laminations in midlength region of

24F–1.8E glulam beams

Level of quality

Percentage of beams

(number)

Low 47 (7)

Medium 13 (2)

High 40 (6)

Figure 5—Rupture of a beam at ultimate load

through the three E-rated laminations on the

tension side and into the No. 3 grade inner

laminations.
10

Table 9—Estimated causes of failure in 24F–1.8E glulam beam combination

Failure typea Number of beamsb

Compression wrinkling followed by rupture on tension side 3

Tension-side rupture in strength-reducing characteristic (other than finger joint) 2

Tension-side in clear lumber 0

Tension-side in finger joint (three had compression wrinkling) 13

a

Tension-side refers to the outer tension laminations of a glulam beam in bending.

b

Sum of all failures is greater than the total number of beams tested (15) as a result

 of beam failures with compression wrinkling.

Table 10—Summary of bending test results on 24F–1.8E and 2 by 4/2 by 6 red maple glulam beams (15 specimens)

24F–1.8E 2 by 4/2 by 6

Normal Lognormal Normal Lognormal

Moisture content ( percent) 12.6 12.6 8.9 8.9

Modulus of rupturea

Average (lb/in2) 7,970 7,980 6,620 6,630

Coefficient of variation ( percent) 12.4 12.1 10.2 10.8

5th percentile at 75 percent tolerance (lb/in2

) 6,010 6,230 5,280 5,320

Adjusted to designb

 (lb/in2) 3,060 3,180 2,340 2,360

Modulus of elasticity

Horizontally laminated

Average (x106

 lb/in2) 1.77 1.86

Coefficient of variation ( percent) 3.0 8.3

Vertically laminated

Average (x106

 lb/in2) 1.87

Coefficient of variation ( percent) 7.1

a

For 24F–1.8E glulam beams, load was applied perpendicular to wide face of laminations;

 for 2 by 4/2 by 6 glulam beams, load was applied parallel to wide face of laminations..

 bAdjusted MOR equals 5th percentile divided by Cv = (5.125/W)0.1 (21/L) 0.1 (12/d) 0.1

 and by 2.1.

Table 11—Results of 15 tension tests on finger-jointed red maple tension

lamination material (specimens with failure involving end joint)a

Property Value

Sample size 15

Average moisture content (percent) 13.1

Average specific gravityb 0.55

Average tensile strength (lb/in2

) 6,490

COV tensile strength ( percent) 27.0

a

Moisture content is based on oven-drying methods.Strength calculations

 assume a lognormal distribution.

b

Based on volume at time of test and ovendry weight
11

Design Strength and

Stiffness Comparison

24F–1.8E Glulam Beams

The design bending strength of the 24F–1.8E glulam beams

is reported in Table 10. The design bending strength level of

3,180 lb/in2 far exceeds the targeted 2,400 lb/in2. The results

in our study are similar to the 24F–1.8E glulam beam results

observed by Manbeck and others (1993), where the design

bending strength for 42 beams from 3 different sizes was

3,150 lb/in2.

For structural finger joints, the ANSI A190.1 standard

requires that the 5th percentiles of finger-joint tensile

strength (at 75 percent tolerance) meets a strength level that

is 1.67 times the targeted design bending strength of the glulam beams. For the 2,400 lb/in2

 glulam in our study, the end

joints were required to meet a 5th percentile tensile strength

of approximately 4,010 lb/in2. From the results shown in

Table 11, a 5th percentile of end-joint tensile strength of

3,480 lb/in2 was calculated, which translates to a design level

of 2,080 lb/in2. The previous discussion on material sorting

explained that sampling of tension lamination grade lumber

for finger-joint specimen fabrication was heavily weighted

towards maximum allowable characteristics of the grade. A

comparison of finger-joint tensile strength in Table 11, with

the red maple finger-joint results from Manbeck and others

(1993), gives some insight on the probable quality of the

finger joints sampled in our study. Only average values were

compared because of the relatively small sample sizes. For

nominal 2 by 6 tension lamination quality finger joints,

Manbeck and others observed an average tensile strength of

8,720 lb/in2

 for the 26 finger joints sampled, which is much

greater than the 6,530 lb/in2 value we observed. However, the

average tensile strength for 16 specimens of 2.0-1/6 finger

joints in the Manbeck and others study had an average of

7,160 lb/in2, which is closer to the average observed in our

study. Thus, it appears that the group of finger joints

Table 12—Results of beam shear strength (τ) for 2 by 4/2 by 6 glulam beam

combination (sample size: 12 beams, 8.9-percent moisture content)

Distribution

Average τ

(lb/in2

)

COV of τ

(%) τ0.05

 at 75% tolerance

Normal 1,730 7.1 1,490

Lognormal 1,730 7.4 1,490

Table 13—Results of ASTM D143 solid wood shear (τ) strength from

failed laminations of 2 by 4/2 by 6 glulam beams (sample size: 25 each)a

Distribution

Average τ

(lb/in2

)

COV of τ

(%)

Average

 MC

(%)

τ

0.05

 at

75%

tolerance (τadjusted)b

Normal

Unconditioned 1,940 11.7 8.7 1,490 362

Conditioned to 12 percent EMC 1,820 8.3 12.7 1,520 371

Lognormal

Unconditioned 1,940 11.8  1,490 364

Conditioned to 12 percent EMC 1,830 8.5  1540 384

a

EMC is equilibrium moisture content; COV is coefficient of variation;

 MC is moisture content based on oven-drying method.

b

(τadjusted) equals τ 0.05 divided by 4.1.
12

sampled for our study had tension lamination grade characteristics that were heavily weighted toward the maximum

allowable characteristics. Because 13 of the 15 beams

exhibiting failures at end joints (Table 9) and glulam beam

results greatly exceeded targeted strength levels (Table 10),

all evidence indicates that the end joints used for beam

manufacture were adequate for the 2,400 lb/in2

 design

bending strength.

For glulam beam bending stiffness, the average MOE

reported in Table 10 was 1.77 × 106 lb/in2. Results show

that the use of E-rated lumber in the beam configuration

(Fig. 1) will achieve the targeted 1.8 × 106 lb/in2 beam stiffness. In addition, as is typical with the use of E-rated lumber

in glulam manufacture, the variability of beam MOE was

quite low (3 percent coefficient of variation).

2 by 4/2 by 6 Glulam Beams

The results in Table 10 show that the calculated design bending strength for the 2 by 4/2 by 6 glulam beam combination

was 2,360 lb/in2, which greatly exceeds the published design

bending stress for No. 2 red maple of 1,450 lb/in2 (AITC

1985). From Table 12, the calculated 5th percentile (at

75 percent tolerance) of horizontal shear strength for the 2 by

4/2 by 6 glulam beams was 1,490 lb/in2. Methods for determining horizontal shear design values from glulam beam test

results are not established. For small, clear test specimens,

design values for horizontal shear strength are determined by

dividing the calculated 5th percentile horizontal shear strength

of ASTM D143 shear-block specimens by a factor of 4.1,

which accounts for a combined effect of duration of load,

stress concentration, and safety. Given that published design

horizontal shear strength for No. 2 red maple glulam with

multiple-piece laminations and having 4 or more laminations

is 65 lb/in2, the results observed in Table 12 would greatly

exceed published values, even with a factor of 4.1.

For bending stiffness, the proposed AITC 119 standard

publishes the same value for orientations loaded with respect

to the y–y and x–x beam axes (see Fig. 1 for orientations).

For No. 2 red maple glulam, the published MOE is

1.3 × 106 lb/in2, which is very conservative compared with

the 1.87 × 106 lb/in2 experimental value observed in the y–y

orientation and the 1.86 × 106 lb/in2 value observed in the

x–x orientation (Table 10).

Predicted Strength and

Stiffness Comparison

In this section, analysis procedures were used to predict the

performance of the glulam test results using the available

lumber properties information.

Bending Strength of 24F–1.8E

Actual MOE data from Table 6 and actual knot property data

from Table 7 were used to predict the performance of the

24F–1.8E glulam combination using ASTM D3737 procedures. Knot property information from Manbeck and others

(1993) was used for the 2.0–1/3 and 1.8–1/3 grades, because

data were not obtained for these grades in our study.

Minimum strength ratios were used as originally planned

(Table 2). For bending stress indices, a value of 3,250 lb/in2

for E-rated lumber having an average MOE of 2.0 × 106

lb/in2 (2.0E) was planned (Table 2). This value is currently

in the ASTM D3737 standard, which is based on a linear

interpolation between a bending stress index value of

3,000 lb/in2 for 1.9E lumber to a bending stress index of

4,000 lb/in2 for 2.1E lumber. In Manbeck and others (1993),

an analysis was made to determine appropriate bending stress

index levels for 2.0E red maple lumber. Based on the analysis

of 42 red maple glulam beams, a bending stress index of

3,500 lb/in2 was found to be applicable for 2.0E red maple

lumber. Thus, we concluded that the bending stress indices

specified in the D3737 standard for E-rated grades of lumber,

which are based on softwood data from past research, are conservative when applied to red maple. Based on the findings of

Manbeck and others, a bending stress index of 3,500 lb/in2

was used in our study for 2.0E red maple lumber, and a

bending stress index of 3,000 lb/in2 was used for 1.8E red

maple lumber.

Analysis of the 12-lamination 24F–1.8E glulam combination resulted in a maximum design glulam bending strength

of approximately 2,800 lb/in2. The analysis indicates that the

calculated strength is controlled by the strength of the region

occupied by the 2.0–1/6 grade. A comparison between the

2.0–1/6 knot properties from our study (x = 1.5 percent and

x + h = 34.8 percent) and those from Manbeck and others

(x = 0.1 percent and x + h = 13.6 percent) shows a significant difference, especially with the x + h values. The knot

properties reported by Manbeck and others for the 2.0-1/6

grade resemble the properties reported in this study for the

tension lamination grade (x = 0.5 percent and x + h = 15.0

percent). When the same combination was analyzed using the

tension lamination knot properties instead of the 2.0–1/6

knot properties from this study, the maximum calculated

design bending strength was 3,080 lb/in2

.

Although the large knot sizes observed in our study could be

attributed to the small sample size, note that another explanation could be the resource of cant-sawn lumber. The gathered

2.0–1/6 material from cant-sawn lumber would likely have

different knot characteristics (e.g., pith-associated wood,

spike knots) than lumber sawn from full-sized logs, such as

used in the Manbeck and others study. Analysis of knot sizes

on two types of timber resources may have resulted in vastly

different knot properties for the two studies. Consequently,
13

this would affect the predicted design bending strength values

using standard ASTM D3737 procedures. Similarities between our study and that of Manbeck and others showed that

D3737 predictions of design bending strength values for

24F–1.8E glulam beams made with E-rated red maple lumber

were very conservative.

24F–1.8E Bending Stiffness

For glulam stiffness, actual lumber MOE values from individual beam maps were used in a transformed section analysis

to predict each individual glulam beam MOE (portions of the

beam map are shown in Appendix C). The calculated glulam

MOE values were then reduced by a factor of 0.95 to account

for shear deformation effects. The transformed section method

of analysis and the 0.95 factor are specified in the ASTM

D3737 standard for calculating horizontally laminated glulam

beam MOE. The individual analyses resulted in a predicted

average glulam beam MOE of 1.85 × 106 lb/in2, having a

coefficient of variation of 2.0 percent. This compares well

with the actual average glulam beam MOE of 1.77 ×

106 lb/in2, having an actual coefficient of variation of

3.0 percent (less than 5 percent difference in the average).

These differences can be attributed to the variations in the

regression relationship shown in Figure 2, which indicates a

coefficient of determination (r2) value of less than 0.9.

2 by 4/2 by 6 Bending Strength

The 2 by 4/2 by 6 glulam beams in our study were evaluated

for loads applied parallel to the wide face of the laminations

(y–y beam axis). The ASTM D3737 standard specifies procedures for determining the design bending strength of vertically laminated glulam beams (Fby). The procedures are based

on the characteristics of the single-ply laminations using the

allowable edge- and center-knot sizes and allowable slope-ofgrain for the particular grade of lumber. For No. 2 red maple

(NELMA 1991), the allowable edge-knot size is 35 percent

of the cross section, allowable center-knot size is 50 percent

of the cross section, and allowable slope-of-grain is 1:8 (1 in.

of grain deviation per 8 in. of length). Because the finished

depth of the beams (width of the vertically oriented laminations) was approximately 7.88 in., an allowable 50 percent

center knot would have a diameter of 3.94 in. and an allowable 35 percent edge knot of 2.76 in. However, because the

laminations in our study were made from a combination of

nominal 2 by 4’s and 2 by 6’s, the largest allowable center

and edge-knot characteristics would be the allowable sizes for

the 2 by 6’s. After planing of the glulam beams, the final

width of the 2 by 6’s was approximately 4.25- to 4.88-in.

wide (based on estimates in Fig. 3). Using a width of

4.88-in., the allowable center and edge-knot sizes would be

2.44 and 1.71 in., respectively.

For No. 2 red maple vertically laminated glulam, D3737

analyses predicted a design bending strength of 1,310 lb/in2

.

This prediction was based on the controlling strength ratio

for slope-of-grain. If the analysis was based solely on the

calculated strength ratios for the allowable knot sizes

(overriding the slope-of-grain strength ratio), the predicted

design bending strength would be 1,550 lb/in2

. Details of the

ASTM D3737 calculations are provided in Appendix D. Note

that the inherent nature of analyzing 2 by 4/2 by 6 glulam

combinations using D3737 procedures would result in greater

predicted design bending strength values than those predicted

for single-member laminations.

In the AITC 119 standard (AITC 1985), the use of twomember laminations is not considered for establishing design

bending stresses for vertically laminated members. Published

design bending stress for vertically laminated glulam beams

(Fby) made from No. 2 red maple lumber is 1,450 lb/in2. All

predicted and published Fby values are very conservative when

compared with the calculated design bending strength of

2,360 lb/in2 given in Table 10.

2 by 4/2 by 6 Bending Stiffness

For stiffness of the 2 by 4/2 by 6 glulam beam combination,

ASTM D3737 procedures were used to determine the glulam

MOE of the members tested in both the horizontally (MOEx)

and vertically laminated (MOEy) orientations. The analysis

resulted in a predicted average glulam beam MOEx of 1.74 ×

106 lb/in2, which is approximately 7 percent less than the

observed value of 1.86 × 106 lb/in2. Predicted glulam MOEy

was 1.75 × 106 lb/in2, which was also approximately 7 percent less than the observed value of 1.87 × 106 lb/in2

. As

was the case with the 24F–1.8E glulam beams, differences

between actual and predicted glulam MOE were attributed to

the variation in the regression relationship of the lumber

properties illustrated in Figure 2.

2 by 4/2 by 6 Horizontal Shear Strength

Procedures are also given in ASTM D3737 for determining

design horizontal shear stresses for vertically laminated

glulam timber. Similar procedures to those shown in

Appendix D for determining 5th percentile of clear wood

MOR were used to determine 5th percentiles of clear wood

shear strength. An 886 lb/in2 clear wood shear strength for

red maple (ASTM 1993c) was multiplied by a 0.222

horizontal shear adjustment factor for hardwoods and a

1.13 seasoning factor, as specified in ASTM D3737. The

resulting horizontal shear stress index of 222 lb/in2 was further reduced by a horizontal shear stress modification factor of

0.5, as a result of the unglued edge joints present in each of

the 2 by 4/2 by 6 laminations. Thus, based on ASTM

D3737 procedures, vertically laminated glulam timber manufactured with 2 by 4/2 by 6 laminations of No. 2 red maple

lumber have a calculated design horizontal shear stress of

111 lb/in2.
14

This value is similar to the design horizontal shear stress of

65 lb/in2 published in the proposed AITC 119 standard.

However, both the predicted and published values are very

conservative when compared with the actual values given in

Table 12.

In addition to establishing design horizontal shear values for

the full-sized glulam beams with ASTM D3737 procedures, a

different approach to determining horizontal shear strength of

glulam timber was studied. Rammer and Soltis (1994)

established a method of predicting the horizontal shear

strength of full-size glulam timber based on the tests of

ASTM D143 shear-block specimens. Results from the

ASTM shear-block tests are shown in Table 13. For shearblock specimens conditioned to 12-percent equilibrium moisture content, the average shear strength of 1,830 lb/in2

 is

almost identical to the average shear strength of 1,850 lb/in2

published in the Wood Handbook (Forest Products Laboratory 1987) for red maple.

Rammer and Soltis (1994) developed a relationship between

average results of ASTM shear-block tests and full-size horizontal shear tests of glulam timber, represented by the following formula:

τ

τ = 1 3

1 5

.

/

C

A

f ASTM (1)

where

τ = average glulam horizontal shear strength (lb/in2),

Cf = 2, a stress concentration factor for an ASTM shearblock notch,

τ

ASTM 

= average shear strength from ASTM D143 test

(lb/in2), and

A = shear area of glulam beam (in2).

Substituting the average ASTM shear-block values

(unconditioned specimens) in Table 13 and the shear area of

the combination glulam beams into Equation (1) resulted in

an estimated average glulam horizontal shear strength of

1,660 lb/in2. This predicted result is within 4 percent of the

actual average horizontal shear strength of 1,730 lb/in2 reported in Table 12. Thus, it appears that the ASTM D143

shear-block approach developed by Rammer and Soltis (1994)

provides more accurate predictions of glulam horizontal shear

stresses than current the ASTM D3737 procedures.

Conclusions

Based on the full-size evaluation of 42 red maple beams, it

was found technically feasible to manufacture structural glulam timber from a cant-sawn hardwood lumber resource.

Specific points observed in this study include the following:

• Structural glued-laminated (glulam) timber beams manufactured with E-rated red maple lumber in the outer zones

and No. 3 lumber in the core met or exceeded the target

design bending stress of 2,400 lb/in2 and modulus of

elasticity (MOE) of 1.8 × 106 lb/in2.

• Structural glulam timber beams manufactured with

laminations made from No. 2 red maple 2 by 4’s and

2 by 6’s are technically feasible. Test results indicate

that target design stresses were exceeded for vertically

laminated bending strength (Fby), MOE in both the horizontally and vertically laminated orientations (MOEx and

MOEy), and horizontal shear strength in the vertically

laminated orientation (Fvy).

• The ASTM D3737 procedures developed for softwood

species accurately predict beam stiffness and provide conservative bending and horizontal shear strength estimates

for glulam beams made with red maple lumber.

• Using results from ASTM D143, shear-block tests accurately predicted the horizontal shear strength of red maple

glulam timber made from 2 by 4/2 by 6 laminations.

References

AITC. 1985. Standard specifications for hardwood

glued-laminated timber. AITC 119-85. Vancouver, WA:

American Institute of Timber Construction.

AITC. 1992. Inspection manual. AITC 200−92. Vancouver, WA: American Institute of Timber Construction.

ANSI. 1992. American national standard for wood products—structural glued laminated timber. ANSI/AITC

A190.1. American National Standards Institute, sponsored by

the American Institute of Timber Construction. Vancouver,

WA: American National Standards Institute.

ASTM. 1993. Standard method for establishing stresses for

structural glued-laminated timber (glulam). ASTM D3737−

93. Philadelphia, PA: American Society for Testing and

Materials.

ASTM. 1993a. Standard methods of static tests of timbers

in structural sizes. ASTM D198−84. Philadelphia, PA:

American Society for Testing and Materials.

ASTM. 1993b. Standard methods of testing small, clear

specimens of timbers. ASTM D143−83. Philadelphia, PA:

American Society for Testing and Materials.

ASTM. 1993c. Standard test methods for establishing clear

wood strength values. ASTM D2555−88. Philadelphia, PA:

American Society for Testing and Materials.

Forest Products Laboratory. 1987. Wood handbook:

Wood as an engineering material. Agric. Handb. 72. (rev.).

Washington, DC: U.S. Department of Agriculture. 466 p.
15

Freas, A.D.; Selbo, M.L. 1954. Fabrication and design

of glued-laminated wood structural members. Tech. Bull.

1069. Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Green, D.W.; McDonald, K.A. 1993. Investigation of

the mechanical properties of red oak 2 by 4’s. Wood and

Fiber Science. 25(1): 35−45.

Janowiak, J.J.; Manbeck, H.B.; Wolcott, M.P.;

Davalos, J.F. 1992. Preliminary refinement of hardwood

stress values. Final Rep. Proj. SS−047. Harrisburg, PA:

Pennsylvania Department of Transportation, Office of

Special Studies.

Janowiak, J.J.; Kessler, K.R.; Manbeck, H.B.;

Blankenhorn, P.R.; Labosky, P. 1994. Compressive

strength properties for two hardwood glulam materials. Forest Products Journal. 44(2): 62−64.

Manbeck, H.B.; Janowiak, J.J.; Blankenhorn,

P.R.; Labosky, P.; Moody, R.C.; Hernandez, R.

1993. Performance of red maple glulam timber beams. Res.

Pap. FPL−RP−519. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

McAlister, R.H. 1973. Edge-glued dimension lumber

from low-grade southern pine. Forest Products Journal.

24(7): 17−22.

McDonald, K.A.; Green, D.W.; Dwyer, J.;

Whipple, J.W. 1993. Red maple stress-graded 2 by 4

dimension lumber from factory-grade logs. Forest Products

Journal. 43(11/12): 13−18.

McDonald, K.A.; Hassler, C.C.; Hawkins, J.E.;

Pahl, T.L. [In press]. Hardwood dimension lumber from

log heart cants. Forest Products Journal.

Metriguard. 1993. Precision testing equipment for wood.

Catalog 20−1. Pullman, WA: Metriguard, Inc.

Moody, R.C.; Hernandez, R.; Davalos, J.F.;

Sonti, S.S. 1993. Yellow poplar timber beam performance. Res. Pap. FPL−RP−520. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

NELMA. 1991. Grading rules for northeastern lumber.

Cumberland Center, ME: Northeastern Lumber Manufacturers Association.

NHLA. 1992. Grading rules for hardwood lumber.

Memphis, TN: National Hardwood Lumber Association.

Shedlauskas, J.P.; Manbeck, H.B.; Janowiak,

J.J.; [and others]. 1994. Efficient use of red oak for gluelaminated beams. ASAE Paper 94−4575. St. Joseph, MO:

American Society of Agricultural Engineers.

Soltis, L.A.; Rammer, D.R. 1994. Shear strength of

unchecked glued-laminated beams. Forest Products Journal.

44(1): 51−57.

Appendix ARelative Quality

Estimates of Red Maple Lumber

Relative quality estimates of red maple lumber used for the

midlength region of tension lamination of 24F–1.8E glulam

beams corresponding to the relative rating system given in

Table 5 are listed for each individual tension lamination in

Table A1. Dynamic MOE values are listed for each piece of

lumber in the critical region. Strength-reducing characteristics

are described for tension laminations of the 24F–1.8E glulam

beams. The MOE values and lamination characteristics correspond to those illustrated in Appendix C.

Table A1Properties of 2 by 6’s used in tension

lamination

Beam

Dynamic

MOE

(×106

 lb/in2)Characteristic

Relative

quality of

midlength

regionb

RM6-1 2.09

2.30

20 percent CK + GD

1:10 S.O.G.

L

RM6-2 1.97

1.93

Clear

1:10 S.O.G.

L

RM6-3 2.19

2.19

Clear

Clear

H

RM6-4 2.19

1.75

Clear

Clear

H

RM6-5 1.94

2.38

Clear

50 percent grain deviation

L

RM6-6 2.06

2.68

Clear

25 percent EK + GD

 (spike knot cluster)

L

RM6-7 1.94

2.24

1:18 S.O.G.

 Clear

L

RM6-8 2.15

1.93

<10 percent CK and GD

Clear

H

RM6-9 1.93

2.05

20 percent GD

Clear

M

RM6-10 1.78

2.14

Clear

Clear

H

RM6-11 1.98

2.19

Clear

1:18 S.O.G.

H

RM6-12 2.04

2.20

1:8 Edge S.O.G.

 30 percent CK + GD

L

RM6-13 2.36

1.90

20 percent CK and GD

<5 percent CK + GD

M

RM6-14 1.97

2.22

<5 percent CK + GD

Clear

H

RM6-15 1.88

2.40

1:10 S.O.G. and 20% t CK

and GD1:20 S.O.G.

L

a

CK is center knot; GD is grain deviation; S.O.G. is slope

 of grain.

b

L is low; M is medium; H is high.
16

Appendix BDestructive Tests

Tables B1 to B5 give the results of the following individual destructive test evaluations:

• Bending tests of horizontally laminated (x) 24F−1.8E red maple glulam beams

• Tension tests on red maple finger-jointed tension lamination grade lumber

• Bending tests of 2 by 4/2 by 6 red maple glulam beams

• Shear strength tests of 2 by 4/2 by 6 red maple glulam beams

• ASTM D143 test evaluation of wood shear strength of failed beam laminations

Table B1—Results of bending tests of horizontally laminated 24F−1.8E red maple glulam beamsa

Dimension

Beam

Beam

weight

(lb)

Width

(in.)

Depth

(in.)

MC

 (%)

Load at

failure

 (lb)

Beam

MORx

(lb/in2)

Beam

MOEx

(x106 lb/in2)

Failure type

(CW,EJ,Lam)

RM6-1 746 5.00 18.03 13.8 28,360 7,161 1.85 EJ

RM6-2 743 5.00 18.03 13.1 33,750 8,503 1.78 EJ

RM6-3 743 5.00 18.09 13.0 40,990 10,240 1.73 EJ

RM6-4 740 5.00 18.11 12.7 27,890 6,982 1.76 EJ

RM6-5 743 5.00 18.10 11.6 31,200 7,808 1.73 EJ

RM6-6 743 5.00 18.05 12.6 35,600 8,945 1.78 EJ

RM6-7 743 5.00 18.05 12.6 36,510 9,172 1.78 EJ

RM6-8 743 5.00 18.05 11.9 32,000 8,050 1.78 CW,EJ

RM6-9 743 5.00 18.06 13.5 27650 6,961 1.83 EJ

RM6-10 743 4.95 18.06 12.0 28,590 7,267 1.78 EJ

RM6-11 743 5.00 18.10 12.3 26,640 6,681 1.82 CW,EJ

RM6-12 743 5.00 18.10 12.4 34,900 8,723 1.67 Lam

RM6-13 743 4.95 18.05 12.7 30,900 7,855 1.79 CW,EJ

RM6-14 743 5.00 18.05 12.0 29,000 7,304 1.76 EJ

RM6-15 743 5.00 18.08 13.0 31,710 7,952 1.67 Lam

a

MC is moisture content based on a resistance-type meter reading; MOR is modulus of rupture;

 MOE is modulus of elasticity; CW is compression wrinkling; EJ is end joint; Lam is lamination.

 Subscript x refers to beams loaded perpendicular to the wide face of the laminations.
17

Table B2—Results of tension tests on red maple finger-jointed tension lamination grade

Specimen

Height

(in.)

Width

 (in.) SG(1)a SG(2)a

Maximum

load

(lb)

Maximum

stress

(lb/in2

)

Failure

zone

RMFJ-1 1.30 4.84 0.51 0.54 39,800 6,317 0,0

RMFJ-2 1.30 4.82 0.53 0.54 25,420 4,047 0,+18

RMFJ-3 1.30 4.83 0.57 0.54 36,960 5,873 −16,0

RMFJ-4 1.30 4.76 0.54 0.51 36,760 5,919 0,0

RMFJ-5 1.30 4.83 0.54 0.57 21,100 3,358 0,0

RMFJ-6 1.31 4.83 0.57 0.54 41,060 6,513 0,+6

RMFJ-7 1.31 4.87 0.54 0.57 68,080 10,666 0,0

RMFJ-8 1.30 4.83 0.62 0.59 45,100 7,179 0,0

RMFJ-9 1.30 4.83 0.52 0.51 40,840 6,497 −24,0

RMFJ-10 1.30 4.84 0.60 0.53 42,260 6,707 0,0

RMFJ-11 1.30 4.84 0.59 0.53 26,520 4,213 0,0

RMFJ-12 1.30 4.83 0.53 0.55 49,280 7,840 0,+8

RMFJ-13 1.31 4.85 0.55 0.59 40,640 6,419 −9,0

RMFJ-14 1.31 4.84 0.52 0.54 49,320 7,802 −4,0

RMFJ-15 1.31 4.83 0.60 0.53 50,710 8,044 −12,0

a

SG is specific gravity based on volume at time of test and ovendry weight; SG(1) and SG(2) refer

 to the specific gravity of lumber on each side of the finger joint.
18

.

Table B3—Results of bending tests of vertically laminated 2 by 4/2 by 6 red maple

glulam beamsa

Beam

Depth

(in.)

Width

(in.)

MC

(%)

Maximum

load (lb)

MORy

(lb/in2)

MOEy

(×106 lb/in2)

MOEx

(×106 lb/in2)

RMC1-1 7.94 6.49 8.5 19,354 7,099 1.92 1.75

RMC1-2 7.95 6.48 8.3 20,419 7,474 1.92 1.82

RMC1-3 7.95 6.48 8.6 15,751 5,766 1.89 1.78

RMC2-1 7.92 6.39 9.1 20,173 7,545 1.88 1.97

RMC2-2 7.91 6.39 9.3 18,759 7,038 1.73 1.56

RMC2-3 7.93 6.42 10.0 17,578 6,529 1.80 1.73

RMC3-1 7.95 6.45 9.3 16,470 6,059 1.87 2.04

RMC3-2 7.94 6.45 9.2 17,592 6,484 1.90 1.82

RMC3-3 7.94 6.46 8.1 16,440 6,064 1.65 1.76

RMC4-1 7.95 6.46 8.7 19,607 7,205 1.84 1.92

RMC4-2 7.97 6.45 8.6 20,274 7,411 1.97 1.91

RMC4-3 7.96 6.46 9.0 17,498 6,418 1.86 1.71

RMC5-1 7.92 6.47 9.3 15,715 5,812 1.88 1.84

RMC5-2 7.96 6.48 8.9 14,664 5,359 1.90 2.02

RMC5-3 7.97 6.20 8.9 18,614 7,087 2.01 2.21

a

MC is moisture content based on a resistance-type meter reading; MOR is modulus of

 rupture; MOE is modulus of elasticity; subscript y refers to beams loaded parallel to the

 wide face of the laminations; subscript x refers to beams loaded perpendicular to the wide

 face of the laminations.

Table B4—Results of shear strength tests of vertically laminated

2 by 4/2 by 6 red maple glulam beams

Beam

Weight

(lb)

Width

(in.)

Depth

(in.)

MCa

(%)

Maximum

 load (lb)

Shear stress

(lb/in2)

b

RMC6-1 108.0 6.48 7.88 8.8 164,800 1,669

RMC6-2 105.8 6.48 7.88 8.6 176,400 1,772

RMC6-3 109.5 6.48 7.88 9.1 196,000 1,985

RMC6-4 103.5 6.50 8.00 8.6 171,200 1,704

RMC6-5 110.0 6.50 7.94 10.8 182,800 1,827

RMC7-1 106.0 6.50 7.88 7.5 170,300 1,715

RMC7-2 110.5 6.48 7.88 8.6 172,600 1,748

RMC7-3 109.0 6.50 7.94 8.5 185,200 1,851

RMC7-4 106.0 6.50 7.88 8.0 176,400 1,772

RMC7-5 110.5 6.48 7.88 9.5 167,000 1,687

RMC10-1 107.0 6.50 8.00 9.0 151,200 1,499

RMC10-2 109.5 6.50 7.94 9.5 157,200 1,565

a

MC is moisture content based on a resistance-type meter reading.

b

Load applied parallel to wide face of the lamination.
19

Table B5—Results of ASTM D143 shear block tests

for failed beam laminations

Block sample

Shear stress

unconditioned

(lb/in2

)

Shear stress at

12% EMCa

(lb/in2)

6-1-3

6-1-5

1,648

2,052

2,156

1,845

6-2-2

6-2-8

1,769

1,926

1,800

1,929

6-3-1

6-3-3

2,443

2,092

1,698

1,932

6-4-2 1,697 1,720

6-5-9 2,026 1,802

7-1-3

7-1-7

2,419

1,901

1,729

1,620

7-2-7

7-2-9

2,149

1,901

2,028

1,620

7-3-2

7-3-4

7-3-8

1,913

1,737

2,066

1,917

1,719

1,897

7-4-7

7-4-9

1,789

1,632

1,590

1,856

7-5-4

7-5-6

7-5-8

1,811

1,823

1,675

1,969

1,615

1,569

10-1-2

10-1-4

10-1-6

2,049

1,930

2,091

2,111

1,877

1,721

10-2-7

10-2-9

1,581

1,979

1,882

1,730

a

EMC is equilibrium moisture content.
20

Appendix CGlulam Beam Failure Maps and Lumber Properties

24F–1.8E Glulam Beams

Location of failure propagation in the tension zone of the beams is given in the following glulam beam failure maps. Failure

through finger joints is reported by an indication of the percentage of the failure that occurred across the finger-joint cross section

(value in brackets). Modulus of elasticity values are given for each piece of lumber in the critical tension zone. Values in parentheses are specific gravity of the lumber based on weight, moisture content, and dimensions taken at time of beam manufacture.

All failure descriptions are given with reference to the centerline of the beam (dimensions are in ft).

Beam No. RM6-1

(0.70) 2.09E

(.80) 2.28E

(0.64) 2.30E

(0.70) 1.98E

(.51) 1.93E

[10%]

[5%]

GD

1:10

Beam No. RM6-3

(0.62) 2.19E

(.61) 1.96E

(0.59) 2.19E

(0.53) 1.90E

(.64) 1.80E

[100%]

Beam No. RM6-5

(0.65) 1.94E

(.67) 1.85E

(0.64) 2.10E

(0.55) 1.73E

(.67) 1.80E

[5%]

50% GD

Beam No. RM6-7

(.74) 2.21E (0.69) 1.94E

(0.66) 2.24E

(0.67) 2.19E

(.58) 1.58E [30%]

[0%]

Beam No. RM6-9

(0.61) 2.06E

(.63) 2.02E

(0.63) 2.05E

(0.70) 1.84E

(.63) 1.84E

[0%]

[75%]

Beam No. RM6-2

(0.63) 1.97E

(.68) 1.99E

(0.64) 1.93E

(0.61) 2.05E

(.68) 2.25E

Beam No. RM6-4

(0.59) 2.19E

(.67) 2.25E

(0.58) 1.75E

(0.62) 1.87E

(.62) 1.68E

[100%]

[30%]

Beam No. RM6-6

(0.58) 2.06E

(.64) 2.09E

(0.65) 2.68E

(0.65) 2.15E

(.63) 1.86E

[100%]

Beam No. RM6-8

(0.63) 2.15E

(.67) 1.98E

(0.65) 1.93E

(0.68) 2.25E

(.66) 1.70E

[30%]

GD

Beam No. RM6-10

(0.63) 1.78E

(.67) 2.08E

(0.64) 2.14E

(0.64) 1.97E

(.62) 1.87E

[5%]

(.64) 1.76E

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5

(.63) 1.67E

(0.70) 2.38E

(.64) 1.68E [75%] (.59) 1.74E (.67) 1.62E (.55) 1.62E

[50%]

(0.58) 1.86E (0.72) 1.90E

(.55) 1.68E (.63) 1.85E

(.70) 2.09E

(0.64) 1.93E

(.66) 2.03E

(.62) 1.88E

(.66) 2.01E

(.66) 1.96E (.59) 1.80E

20% CK+GD 1:10

25% EK+GD

1:8 <10% EK+GD

20% GD
21

Beam No. RM6-11

(0.63) 1.98E

(.68) 2.17E

(0.69) 2.19E

(0.61) 2.10E

(.63) 1.69E [100%]

Beam No. RM6-13

(0.64) 2.26E

(.68) 2.16E

(0.73) 2.36E

(0.62) 1.87E

(.58) 1.79E

[0%]

Beam No. RM6-15

(.69) 2.28E

(0.64) 2.40E

(0.61) 2.13E

(.67) 1.83E

[10%]

Beam No. RM6-12

(0.65) 2.04E

(.67) 2.07E

(0.63) 2.20E

(0.64) 2.02E

(.64) 1.95E

[2%]

Beam No. RM6-14

(0.55) 1.97E

(.62) 2.01E

(0.62) 2.22E

(0.71) 2.08E

(.60) 1.79E

[100%]

[30%]

(.65) 1.67E

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5

(.66) 2.09E

(0.68) 1.88E

(.57) 1.78E

(.58) 1.81E (.64) 1.70E E.K. + G.D.

[100%] (0.65) 1.90E

(.63) 1.82E (.61) 1.70E

(0.57) 1.63E

(0.62) 2.00E

30% CK+GD

1:18 1:8

20% CK+GD <10% CK+GD <5% CK+GD

1:10 1:20

20% CK+GD
22

2 by 4/2 by 6 Combination Beams

Horizontal shear failure through the cross sections of the 2 by 4/2 by 6 combination glulam beams are illustrated

in the following:

2 3

RMC6-1

3

RMC6-4 RMC7-1

RMC6-2

RMC7-4

RMC10-2

RMC6-3

RMC7-3

RMC6-5

RMC7-5 RMC10-1

RMC7-2

1

Key

5

2345

6 7 8 9 10

TOP

BOTTOM

7

2

8

2 4

8

9

7 9

6

4 2 4

6 8 7 9

1 3

7 9

Numbers in key correspond to

shear-block specimen locations

and their identification numbers
23

Appendix DASTM Procedures

The following calculations document ASTM D3737 procedures for determining design bending strength for the 2 by

4/2 by 6 glulam combination with loads applied parallel to

the wide face (vertically laminated). The procedures involve

four steps that determine the following:

1. Bending stress index for red maple using ASTM D2555

procedures

2. Critical strength ratios for the No. 2 red maple lumber

using ASTM D245 procedures

3. Critical stress modification factors based on ASTM

D3737 criteria

4. Design bending strength from calculated information

Bending Stress Index

5th percentile of clear wood modulus of rupture from ASTM

D2555, Table 2.

 CWS5th = 7,690 lb/in2 - 1.645 (1,230 lb/in2) = 5,667 lb/in2

Bending adjustment factor for hardwoods from ASTM

D3737, Table 1.

BAF = 0.435

Seasoning factor from ASTM D3737, Table 1.

SEAS = 1.35

Size factor to adjust to a 12-in. deep, uniformly loaded

simple beam with a 21:1 span-to-depth ratio.

 SIZE = 0.743

Multiply all factors to get bending stress index (BSI).

BSI = 2,473 lb/in2

Critical Strength Ratio

Wide face dimension of laminating lumber h = 4.875-in.

Narrow face dimension of laminating lumber b = 1.3-in.

Size of center knot based on width of k1 = 2.44-in.

 resurfaced 2 by 6

Size of edge knot based on width k2 = 1.71-in.

 of resurfaced 2 by 6

Strength ratio for center knots on wide face of lumber using

ASTM D245 procedures

SR1 100 1 k 1/24

h 3/8 = −  −



 



 



 



 1

+

SR1 = 54.4%

Strength ratio for edge knots on wide face of lumber using

ASTM D245 procedures.

SR2 100 1 k 1/24

h = −  −











 





2 2

SR2 = 43.4%

Critical strength ratio is governed by edge knots (SR2

controls).

SR = 0.434

Critical Stress Modification Factor

Stress modification factor for knots from ASTM D3737.

SMF C (SR) N

N

1 1 = − 



 



 γ α 1 1 645 1

0 5 . .

Ω

where

C1 = 1.256 (ASTM D3737, Table 5)

γ = 0.81 (ASTM D3737, Section 7.2.2.1)

α = 0.329 (1 − 1.049 SR) (ASTM D3737, Section 7.2.2.1)

Ω1= 0.36 (ASTM D3737, Section 7.2.2.1)

N = 5 (for 5-lamination glulam beam)

Substitute all factors to get stress modification factor for

knots.

SMF1= 0.626

Stress modification factor for slope of grain.

SMF2 = 0.53 from ASTM D3737, Table 4.

Critical stress modification factor is governed by slope of

grain (SMF2 controls).

SMF = 0.53

Design Bending Strength

Multiply clear wood bending stress index by critical stress

modification factor to get glulam design bending stress.

Fb = 1,311 lb/in2

If calculations were based only on the size of knots (ignore

critical stress modification factor for slope of grain), the calculated glulam design bending stress would be

Fb = 1,549 lb/in2