Yellow Poplar Glulam Timber Beam Performance

United StatesDepartment ofAgriculture

Forest Service

ForestProductsLaboratory

ResearchPaperFPL-RP-520

Yellow PoplarGlulam TimberBeam PerformanceRussell C. MoodyRoland HernandezJulio F. DavalosSomnath Sharma Sonti

Abstract Contents

Yellow Poplar is currently not used in structural glued-laminated (glulam) timber construction, but its prop-erties suggest that it may be feasible for this purpose.Using Yellow Poplar, we designed glulam beam combi-nations to target bending stresses of 2,400 lb/in2 andmodulus of elasticity of 1.8 × 106 lb/in2. The glulamcombinations were designed with E-rated lumbergrades in 25 percent of the outer laminations (top andbottom) and No. 2 grade lumber in 50 percent of thecenter laminations. In addition to evaluating 45 full-sized beams, more than 200 end-jointed lumber spec-imens were tested in tension to compare individualspecimen performance to full-size beam performance.Results for the Yellow Poplar glulam beams met thetarget design levels, indicating that this species is afeasible candidate for structural glulam construction.

Keywords: Laminated wood, hardwood, glulam,E-rated, Yellow Poplar, modeling

June 1993

Moody, Russell C.; Hernandez, Roland; Davalos, Julio F.;Sonti, Somnath Sharma. 1993. Yellow Poplar glulam tim-ber beam performance. Res. Pap. FPL-RP-520. Madison,WI: U.S. Department of Agriculture, Forest Service, ForestProducts Laboratory. 28 p.

A limited number of free copies of this publication areavailable to the public from the Forest Products Labo-ratory, One Gifford Pinchot Drive, Madison, WI 53705-2398. Laboratory publications are sent to more than 1,000libraries in the United States and elsewhere.

Page

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

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

Objective and Scope . . . . . . . . . . . 3

Experimental Design . . . . . . . . . . 3

Materials and Methods . . . . . . . . . 4

Procurement . . . . . . . . . . . . 4

Lumber Grades and Properties . . . . 5

Fabrication . . . . . . . . . . . . . 6

Beam and End-Jointed Lumber . . . . 7

Strength and Stiffness . . . . . . . . 9

Analysis . . . . . . . . . . . . . . . . 11

Beam Size . . . . . . . . . . . . . 11

Design Levels . . . . . . . . . . . . 11

Comparison With Predicted Values. . . . . 12

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

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

Appendix A—Tension Test Results . . . . 16

Appendix B—Glulam Beam Results andFailure Descriptions . . . . . . . . . . . . . . 19

The Forest Products Laboratory is maintained in coopera-tion with the University of Wisconsin.

Yellow Poplar Glulam TimberBeam Performance

Russell C. Moody, Supervisory Research General Engineer

Roland Hernandez, Research General Engineer

Forest Products Laboratory, Madison, Wisconsin

Julio F. Davalos, Assistant Professor

Somnath Sharma Sonti, Research Engineer

West Virginia University, Morgantown, West Virginia

Introduction Table 1—SI conversion factors

English unit Conversion factorThe economical and efficient use of timber in engi-neered structures, such as long-span roofs and bridges,is practical with structural glued-laminated (glulam)timber. Long-span glulam beams are needed for tim-ber bridges of conventional deck-and-stringer designand stress-laminated systems consisting of T- and box-section design (Ritter 1990). Douglas Fir and SouthernPine lumber are primarily used for glulam timber; how-ever, using an underutilized hardwood species, such asYellow Poplar, would be advantageous. Yellow Poplaris abundant in areas of Virginia and West Virginia.These areas also have a need for several bridges in thespan ranges obtainable with glulam timber. Thus, theuse of Yellow Poplar for a value-added product such asglulam timber could enhance industrial development inthese areas.

foot (ft)inch (in.)board footpound per cubic

foot (lb/ft3)(weight)

ton (metric)pound per square

inch (lb/in2)(stress)

pound-force (lbf)degree Fahrenheit

(°F)

0.304825.4

0.0021.60

1,000

6.895 kilopascal (kPa)4.448 newton (N)

Background

The use of Yellow Poplar veneer for manufacturingsmall laminated beams was investigated by researchersin Pennsylvania during World War II (Norton 1943,Nearn and Norton 1952). As expected, the mechani-cal properties of these laminated veneer lumber (LVL)beams were comparable to those of clear wood.

Several studies have investigated the properties ofYellow Poplar structural lumber. Koch and Rousis(1977) studied the effectiveness of using modulus ofelasticity (MOE) and specific gravity as predictors ofthe bending strength of Yellow Poplar. They foundthat for clear wood samples, MOE and specific grav-ity exhibited good correlation with strength properties;however, the strength properties of clear wood samples

were not useful for predicting the strength of lumbercontaining defects, such as knots, checks, and shakes.Based on the experimental work performed by Maeglin(1978), Gerhards (1983) studied the effect of high-temperature drying on the bending strength of nomi-nal 2- by 4-m. (2 by 4) Yellow Poplar. (See Table 1 formetric conversions.) Gerhard’s study showed that 2 by4’s processed with high-temperature drying have negli-gibly lower bending strength than lumber produced byconventional sawing and drying. Also, he found thatmachine grading could be applicable to Yellow Poplarbecause of the high correlation between MOE and mod-ulus of rupture (MOR). Stern and Dunmire (1972)conducted an extensive study on strength propertiesof Yellow Poplar. They observed that strength prop-erties increased with increases in specific gravity anddecreased with rapid rates of growth.

SI unit

meter (m)millimeter (mm)cubic meter (m3)kilogram per

cubic meter

(kg/m3)kilogram (kg)

Celsius (°C)

Green and Evans (1987) evaluated Yellow Poplaras part of the In-Grade Lumber Testing Program.Table 2 gives a comparison of the bending and tensilestrength properties of visually graded Yellow Poplarand Southern Pine lumber from that study. Table 2also compares bending and tensile design propertiesfrom the National Design Specification (NDS) forthe same grades and species of lumber (NFPA 1991).Bending strength of Select Structural Yellow Poplarlumber was up to 15 percent lower than that of South-ern Pine lumber, whereas tensile strength was compara-ble for the same grade. However, No. 2 Yellow Poplarwas comparable in bending strength and significantlygreater in tensile strength than was the same grade ofSouthern Pine. These data are not consistent with de-sign property information from NDS in which YellowPoplar is assigned much lower design stresses in bothbending and tension, either about 50 percent (SelectStructural) or 70 percent (No. 2) of Southern Pine.

Table 3 compares the MOE of Yellow Poplar andSouthern Pine lumber. Test results and the NDS agreethat the Select Structural Yellow Poplar/SouthernPine ratio is 0.83. The MOE ratio from tests on No. 2Yellow Poplar/Southern Pine is about 0.89 and 0.95,but NDS gives a lower ratio of 0.81.

Data in Tables 2 and 3 suggest that NDS proceduresused to develop the design properties of Yellow Poplarmay be quite conservative and that much of the mate-rial would be underutilized using present design values,particularly the No. 2 grade lumber. The current ap-proach to developing design values for Yellow Poplaris understandable, because the sample size of YellowPoplar lumber (Green and Evans 1987) was less thanthat for Southern Pine and there has been little ex-perience with Yellow Poplar in engineered structuralapplications.

Freas and Selbo (1954) published basic property infor-mation for Yellow Poplar from which design propertiesfor glulam timber could be developed. The propertyinformation was based on clear wood data without ac-tual tests of Yellow Poplar glulam timber beams. Sincethen, Yellow Poplar has been included in various spec-ifications for hardwood glulam timber, most recentlyin AITC 119 (1985). In AITC 119, design stresses inbending are limited to 1,600 lb/in2 for beams madefrom high-grade lumber, and MOE for these beams islimited to 1.5 × 106 lb/in2.

Test data are not available on the strength of glulamtimber beams made of Yellow Poplar lumber. The lit-erature on mechanical properties of visually gradedYellow Poplar suggests that it may be underratedin strength and stiffness properties. The potentialuse of Yellow Poplar in glulam timber needs careful

2

Table 2—Average bending and tensile strength propertiesof Yellow Poplar and Southern Pine lumber(adjusted to 15 percent moisture content)

Propertyand grade

Strength Yellow(lb/in2) Poplar/

SouthernSize Yellow Southern Pine(in.) Poplar Pine ratio

Bending a Select Structural 2 by 4No. 2Select Structural 2 by 8No. 2

Tensile a

Select Structural 2 by 4No. 2

Design bending b

Select Structural 2 by 4No. 2Select Structural 2 by 8No. 2

Design tensile b

Select Structural 2 by 4No. 2Select Structural 2 by 8No. 2

9,180 10,920 0.848,030 7,540 1.068,040 8,720 0.926,310 6,220 1.01

6,760 6,560 1.034,950 3,380 1.46

1,500 2,850 0.531,050 1,500 0.701,200 2,300 0.52

840 1,200 0.70

863 1,600 0.54600 825 0.73690 1,300 0.53480 675 0.71

a Green and Evans 1987.b NFPA 1991.

Table 3—Average MOE of Yellow Poplar andSouthern Pine lumber (adjusted to 15 percentmoisture content)

Propertyand grade

Strength Yellow(lb/in2) Poplar/

SouthernSize Yellow Southern Pine( i n . ) P o p l a r Pine ratio

MOE a

Select Structural 2 by 4 1.50 1.82 0.82No. 2 2 by 4 1.45 1.53 0.95Select Structural 2 by 8 1.58 1.89 0.84No. 2 2 by 8 1.43 1.60 0.89

Design MOE b

Select Structural All 1.50 1.80 0.83No. 2 All 1.30 1.60 0.81

a Green and Evans 1987.b NFPA 1991.

evaluation, particularly with an alternative grad-ing method such as E-rating that could improve thegrading efficiency.

Objective and Scope

The objectives of this study were to develop and ver-ify a basis for a specification for Yellow Poplar glulamtimber. A total of 45 glulam timber beams were man-ufactured and evaluated. In addition, more than 200end-jointed lumber specimens were tested in tension tocompare individual specimen performance to full-sizebeam performance.

Experimental Design

Prior to procuring materials and manufacturing theglulam beam combinations for this study, it was nec-essary to determine the following factors for designingthe targeted glulam combinations: minimum strengthratios, bending stress indices, knot properties, MOElevels of E-rated grades of lumber, potential yields ofYellow Poplar, and end-joint qualification levels.

To design the glulam beam combinations using presentprocedures, several assumptions were made to estab-lish the minimum strength ratio, bending stress in-dices (clear wood stress), and knot properties. Mini-mum strength ratios of the candidate grades of YellowPoplar were estimated from similar species of lumberlisted in AITC 117 (1979). Bending stress indices forthe proposed E-rated grades were those recommendedby ASTM D3737 (1992a). Knot properties for each ofthe proposed grades of Yellow Poplar lumber were esti-mated using actual knot measurements obtained from astudy on red maple lumber (Manbeck and others 1993).

In addition to strength ratios and knot information,ASTM D3737 procedures require using the averagelong-span static bending MOE values for each gradeof lumber. This study used E-rated lumber in the beamlayup. Thus, it was necessary to determine if the cur-rent resource of Yellow Poplar structural lumber wouldprovide adequate yields of the desired E-rated grades.Previously noted studies on Yellow Poplar structurallumber were reviewed to determine potential yields.The issue of end-joint performance also needed to beaddressed. Information on Yellow Poplar end-jointedlumber did not exist; therefore, it was necessary to de-termine its performance level.

Based on information from past research of YellowPoplar lumber, it was estimated that a target glu-lam design bending stress of 2,000 lb/in2 and MOE of1.6 × 106 lb/in2 could be achieved. However, after

Table 4—Assumed properties of Yellow Poplarlumber grades for ASTM D3737 procedures

Grade

BendingMOE Average Maximum stress(×106 knot knot indexlb/in2) (%) (%) (lb/in2)

2 .0- l /6 2.0 3.0 27.0 3,2502.0- l /3 2.0 5.0 30.0 3,2501.8-l/3 1.8 5.0 30.0 2,850No. 2 1.5 8.0 42.0 1,910

evaluating the stiffness of the lumber that was pur-chased for beam manufacture, we determined that thesample of lumber possessed significantly greater MOElevels than expected. Therefore, the target glulam de-sign bending stress was increased to 2,400 lb/in2 andthe target MOE level increased to 1.8 × 106 lb/in2.The lumber properties in Table 4 were used to developa new glulam beam combination.

To determine if Yellow Poplar end joints would meetANSI A190.1 (1992) criteria for design bending stressesof 2,400 lb/in2, samples of 2 by 4 and 2- by 6-in.(2 by 6) lumber were gathered for tension tests. Theend joints were manufactured from clear Yellow Poplarlumber at the laminating plant selected for beam man-ufacture. Although all end-joint specimens were clear,some did not meet tension lamination criteria as a re-sult of slope-of-grain limitations. Most failures exhib-ited high overall wood failure, and apparent problemswere not observed with the glue bonds. On severalspecimens showing a high percentage of wood failure,we observed that the mineral-stained characteristicsof the Yellow Poplar lumber were involved in the fail-ure. The results in Table 5 show that both 2 by 4 and2 by 6 end joints would meet ANSI A190.1 tensilestrength requirements, even with the slope-of-grainmaterial included in the analysis. Therefore, the tar-geted design levels of 2,400 lb/in2 bending stress and1.8 × 106 lb/in2 MOE appeared to be reasonable.

Three beam combinations were designed to representcritical beam sizes with small, medium, and large di-mensions (Fig. 1). The smallest had 8 laminations withdimensions of 3 in. wide by 11 in. deep by 20 ft long;the medium had 12 laminations with dimensions of5 in. wide by 16.5 in. deep by 30 ft long; the largesthad 17 laminations with dimensions of 6.75 in. wideby 23.375 in. deep by 40 ft long. The three beam sizeswere manufactured using nominal 2 by 4, 2 by 6, and2- by 8-in. (2 by 8) lumber, respectively.

These glulam combinations were designed with E-ratedlumber in the outer and adjacent inner zones and visu-ally graded lumber in the core. Specifically, the beams

3

Table 5—Results of tension tests on independentsample of Yellow Poplar end joints a

Property

Sample sizeMoisture content (%)Specific gravity

Lognormal distribution

2 by 4 2 by 6

23 2611.1 12.00.47 0.45

Average tensile strength (TS) 7,020 7,080(lb/in2)

Coefficient of variation of TS 19.3 13.4

(%) at 75% tolerance 4,680 5,390

a Failures not associated with the end joints werenot included in the analysis.

contained 2.0E material in the outer zones, 1.8E mate-rial in the adjacent inner zones, and No. 2 material inthe core laminations. Lumber used for the two zoneson the compression side of the beams and for the nextinner zone on the tension side had a knot limitationof one-third the cross section along the edge. Conse-quently, the 2.0E material (on the compression side)was designated as 2.0-1/3, and the 1.8E material wasdesignated as 1.8-1/3. These two grades represent No.2 or better lumber. Lumber in the outer tension zonehad an edge knot limitation of one-sixth the cross sec-tion. This material was designated as 2.0-l/6. Specialgrades were developed for the outer 5 percent of thetension laminations following ASTM D3737, and crite-ria for these grades are given in Table 6.

For each beam size, a sample size of 15 beams was se-lected based on the criterion to be able to detect abouta 10-percent significant difference in strength propertiesfor each beam size with a 90-percent confidence level.Thus, a total of 45 beams were manufactured.

Materials and Methods

This section discusses procurement, sawing, yield, grad-ing, and properties of Yellow Poplar lumber as well asfabrication of end joints and full-size beams.

Procurement

Logs were obtained from the southwestern part ofWest Virginia. The trees that were selected for cuttingranged in diameter from 12 to 24 in. at breast height.The trees varied from 25 years to more than 50 yearsold. The majority of the trees exhibited crook charac-teristics approximately 24 to 30 ft above the groundthat were caused by inclement conditions such as snow-

4

Figure 1--Yellow Poplar glulam combinations showing place-ment of lumber grades for the 8-. 12-. and 17-laminationbeams.

Table 6—Tension lamination criteriarequired by ASTM a

Beam group

Criterion 8-Lam 12-Lam 17-Lam

Edge knot plus graindeviation

Center knot plus graindeviation

Slope of grain

0.45 0.30 0.30

0.50 0.40 0.35

1:14 1:16 1:16

a Knots plus grain deviations given indecimal parts of cross section (ASTM 1992a).

fall and wind. Trees with these defects were a majorcomponent of those selected because procurement ofa sufficient low-grade material was a major concern inthis study.

Cant sawing was used to obtain the maximum pos-sible yield from the available logs. Cant sawing iswidely used for softwoods and structurally graded hard-woods. The objective of using this sawing methodwas to have the midsurface of each piece coincidewith a line bisecting the log. It was observed that the2 by 8’s were less likely to warp than were the 2 by 4’sand 2 by 6’s.

Table 7—Quantity of Yellow Poplar lumber in various grades and sizes

Nominal Boardsize length(in.) (ft)

Lumber yield (board feet)

Select Structural No. 1 No. 2 No. 3 Total

Sawn Graded Sawn Graded Sawn Graded Sawn Graded Sawn Graded

2 by 4 16 1,056 963 528 510 1,108 1,038 327 298 3,019 2,80914 27 23

20337 18 37 37 101 78

12 126 124 221 380 332 95 89 846 74810 6 6 20 19 13 10 6 6 46 41

8 137 130 195 185 153 143 73 66 570 5282 by 6 16 2,032 1,924 1,568 1,518 2,768 2,584 562 536 6,930 6,562

14 200 240 70 66 252 236 56 54 244 22612 540 518 660 640 1,980 1,820 360 340 3,408 3,196

8 328 316 312 292 880 832 272 248 1,392 1,2922 by 8 16 5,681 5,327 1,350 1,294 4,738 4,536 407 394 12,176 11,551

14 337 311 93 85 581 557 168 150 1181 1,10312 1,993 1,902 675 651 3,762 3,589 1,013 925 7,445 7,131

8 1,232 1,203 675 650 1,500 1,417 525 495 4,137 3,969

a No 14-ft-long specimens.

The total yield from logs was 46,500 board feet, eachlog ranging in length from 8 to 16 ft. The total vol-ume of sawn lumber obtained from the logs was41,495 board feet, a yield of 89.5 percent. The totalvolume of graded lumber obtained after trimming was39,234 board feet, a yield of 94.6 percent. Quantities ofsawn lumber for the various sizes and grades are sum-marized in Table 7.

Lumber Grades and Properties

The sawn lumber at the mill was visually graded intoSelect Structural, No. 1, No. 2, and No. 3 using na-tionally recognized grading rules (NELMA 1991).

Special care was taken to evaluate and control the lum-ber properties used in the beams. This was so thatthe final results of the beam tests would be meaning-ful when establishing a specification on Yellow Poplarglulam beams.

The grades listed in Table 4 needed to meet both theMOE criteria in AITC 117–Manufacturing (AITC1988) and the edge-knot criteria established in lum-ber grading standards for E-rated grades. Therefore,during the testing for MOE, each piece of lumber wasinspected and graded as a candidate for one of the fourvisually graded categories: tension lamination, 1/6 edgeknot, 1/3 edge knot, and No. 2.

The MOE was determined using commercially avail-able equipment, utilizing transverse vibration nonde-structive techniques (Ross and others 1991). Long-span

static bending deflection readings were taken at randomthroughout the testing to ensure that the transverse vi-bration equipment was properly calibrated. Figure 2illustrates the relationship between static and dynamicMOE measurements. Because the difference betweenstatic and dynamic MOE was small, the actual dy-namic MOE values were used, and data adjustmentswere not made. Dimensions of the lumber were mea-sured using a standard tape measure, and moisturecontent levels were measured using a resistance-typemoisture meter. Identification numbers were stampedon the narrow edge of each piece of lumber, such thatthe lumber specimens could easily be located followingbeam fabrication. In addition, measured MOE valueswere written on the ends of the lumber for later usewhen sorting. The sorting scheme used to achieve thetarget MOE distributions is described in Table 8.

To accurately analyze the beams for bending strengthusing ASTM D3737 procedures, knot sizes were mea-sured for each grade of lumber after the lumber wassorted by MOE. Knot sizes were measured by estimat-ing the diameter of an equivalent “straight-through”knot; this was done for all tension lamination materialand for representative samples of the remaining gradesof lumber. Analysis of the knot data was conducted us-ing a program that followed the principles in Freas andSelbo (1954).

The results of lumber sorting to achieve the targetMOE values are presented in Table 9. Only thoselumber specimens that appeared in the fabricatedbeams are included in the averages. The results in

5

Dynamic MOE (x106 lb/in2)

Figure 2—Relationship between dynamic MOE and staticMOE.

Table 9 show that the target MOE level for each gradeof lumber was generally achieved; an exception was the1.8-1/3 grade for the 2 by 8’s. The sorting of thisgrade resulted in a MOE level of 1.69 × 106 lb/in2.Therefore, the static bending MOE results of the17-lamination beams were expected to be slightly lessthan those of the 8- and 12-lamination beams.

The knot measurement information was transferredfrom prepared data sheets to a spreadsheet for subse-quent analysis. Table 10 lists the results of the knotsize calculations based on measurements from morethan 6,000 lineal ft of lumber. These data were re-quired as input for ASTM D3737 (1992a).

In addition to the three manufactured beam configura-tions (Fig. 1), specimens were prepared for end-jointedlumber tests. The location of each lumber piece withineach beam was recorded on maps so that the lumberproperties could later be related to beam performance.In addition, the quality of the critical tension lamina-tions was assessed, in relation to the allowable knot andslope-of-grain properties, to determine the relative qual-ities of the beams.

Fabrication

The Yellow Poplar lumber was end-jointed using amelamine adhesive and cured in a radio-frequency tun-nel at 200°F. The full-length laminations were thencut to length and stacked according to the designatedbeam layups. At this point, the location of each pieceof lumber was recorded (using the numbers that werestamped on the narrow edge) on prepared beam maps.The beams were then visually inspected to ensure con-formance to ANSI A190.1 and determine the relativequalities of the tension laminations in the midlengthregion that would be subjected to 85 percent or more

6

Table 8—Target MOE values and detailsof sorting scheme

Grade Sorting and grading criteria

2.0–1/6 Average MOE of 2.0 to2.1 × 106 lb/in2

No MOE value <1.60 × 106 lb/in2

5th percentile at 1.67 × 106 lb/in2

No MOE value >2.4 × 106 lb/in2

Edge-knot limitation, 1/6

2.0–1/3 MOE restrictions are the sameas above; edge-knot limitation, 1/3

1.8–1/3 Average MOE of 1.8 to 1.9 × 106 lb/in2

No MOE value <1.40 × 106 lb/in2

5th percentile at 1.45 × 106 lb/in2

No MOE value >2.2 × 106 lb/in2

Edge-knot limitation, 1/3

No. 2 No MOE restrictions

Table 9—Results of testing and sortingscheme for MOE

Size and grade

Average COVa

Samples i z e ( × 1 0 6 l b / i n 2 ) ( % )

2 by 4Tension lamination2.0–1/31.8–1/3No. 2

2 by 6Tension lamination2.0–1/62.0–1/31.8–1/3No. 2

2 by 8Tension lamination2.0–1/62.0–1/31.8–1/3No. 2

23 2.01 7.824 1.99 7.665 1.80 9.569 1.83 8.1

38 2.07 7.358 1.96 9.887 2.03 8.4

100 1.84 12.1185 1.88 10.7

54 2.02 9.453 2.01 8.8

106 2.02 9.1225 1.69 11.8340 1.85 14.5

a COV = coefficient of variation.

of the maximum moment during testing. Using thetension lamination criteria listed in Table 6, a rela-tive rating system was developed to categorically as-sign a quality to the tension lamination. Table 11 liststhe allowable percentages of lumber cross-sectionalareas that can be occupied by knots, the slope-of-grainlimitations, and the MOE restrictions for a classifica-tion of low, medium, or high quality.

Table 10—Knot properties of laminatinglumber

Size and grade

Totallength

(ft) (%) (%)

2 by 4Tension lamination 404 0.82.0–1/3 294 0.31.8–1/3 630 1.5All 1/3 edge knot 924 1.1No. 2 441 3.0

2 by 6Tension lamination 501 0.52.0–1/6 463 2.22.0–1/3 168 5.01.8–1/3 191 4.1All 1/3 edge knot 359 4.5No. 2 178 6.6

2 by 8Tension lamination 691 1.12.0–1/6 451 1.92.0–1/3 492 4.01.8–1/3 615 5.3All 1/3 edge knot 1,107 4.7No. 2 574 6.6

20.613.532.428.349.5

12.629.145.633.041.142.5

25.921.042.440.341.845.4

= average of sum of all knot sizeswithin each 1-ft length, taken at 2-in.intervals (ASTM 1992a).

= 99.5 percentile knot size(ASTM 1992a).

The full-length laminations were then face-planed toa uniform thickness of 1.375 in. and laminated with aphenol–resorcinol adhesive. The full-sized beams wereclamped at a pressure of 150 lb/in2 and cured overnightat approximately 90°F. The cured beams were thenedge-planed to uniform widths of 3, 5, and 6.75 in. forthe 8-, 12-, and 17-lamination beams, respectively.

Another requirement in the development of a new glu-lam combination is the assurance that the end jointsmeet certain tensile strength levels. In this study, ad-ditional end-joint specimens from each lumber gradewere gathered for subsequent tension tests. For boththe 2 by 4’s and 2 by 8’s, end-jointed specimens wereobtained during manufacture of the respective gradesof lumber for the beams. A slightly different procedurewas used for the 2 by 6 end-jointed specimens, as de-scribed in the following paragraph. The informationobtained from these laboratory tests will aid in the per-formance comparison of the end-jointed specimens tothe full-sized beams.

As stated, 2 by 6 end-jointed specimens wereobtained differently than were the 2 by 4 and 2 by 8end-jointed specimens. A matching group of tensionlamination quality material was needed for a subse-quent research study regarding preservative treatmentof Yellow Poplar. The intent of this subsequent studywas to obtain a test group treated and untreated ofsolid-sawn and end-jointed 2 by 6 lumber specimens.To obtain “matching” groups of solid-sawn lumber, thespecimens were equally sorted by MOE into two match-ing groups: one group treated with preservatives andthe other group untreated (control). Thirty specimenswere gathered in each group such that the distributionof MOE for each was identical. To obtain “matching”groups of end-jointed specimens, two full-length boardswere used to fabricate two end-jointed specimens bycutting one board in half (cross-cut) and joining thetwo halves to each end of the second full-length pieces.To obtain a range in quality in each test group, a rangeof MOE lumber pairs was used on each side of the endjoint. For example, a low MOE board was end jointedto a high MOE board. Thirty end-jointed specimenswere gathered for each test group such that identicaldistributions of MOE pairs were obtained.

Forty-five Yellow Poplar timber beams were man-ufactured and inspected to meet the require-ments of AITC (1992). The percentages of beamsthat were categorized as having low-, medium-,or high-quality tension laminations are shown inTable 12. Additional details on the qualities ofthe individual tension laminations are provided inAppendix A.

End-jointed lumber samples obtained for the tensionlamination grade are listed in Table 13, and the re-maining grades are listed in Appendix A. A total of254 specimens were gathered for all grades and widths.

Beam and End-Jointed Lumber

Testing equipment and procedures for evaluating theglulam beams and the end-jointed lumber specimensfollowed criteria in ASTM D198 (ASTM 1992b).

Beams

The loading configuration used to test the full-sizedbeams is illustrated in Figure 3. Physical properties(moisture content, weight, and dimension), stiffnessproperties (full-span deflection), and failure load weremeasured for each beam. Moisture content levels weremeasured with a resistance-type moisture meter at thecentral midspan of all laminations after failure of thebeam. The weight of each beam was measured witha scale supported by a 10-t crane. Dimensions weremeasured at each load point.

7

Table 11—Relative rating system for tension lamination qualitya

Beam group Permittedand criteria values Low

Quality

Medium High

8-LamEK + GD (%)CK + GD (%)Slope of grainMOE (× 106 lb/in2)

12-LamEK + GD (%)CK + GD (%)Slope of grainMOE (×106 lb/in2)

17-LamEK + GD (%)CK + GD (%)Slope of grainMOE (×106 lb/in2)

45501:142.0E (Avg)

30401:162.0E (Avg)

30351:162.0E (Avg)

>30>35>1:16<1.7E with

characteristic

>20>30>1:18<1.7E with

characteristic

>20>20>1:18<1.7E with

characteristic

15 to 3020 to 351:16 to 1:18<1.7E and clear



<15<20>1:18

<10<15>1:20

<10<10>1:20

a EK = edge knot; CK = center knot; GD = grain deviation.

Table 12—Relative quality of tensionlaminations in midlength region ofbeams

Quality (%)

Beam groupa Low Medium High

8-Lam 40 33 2712-Lam 27 20 5317-Lam 40 27 33

a 15 beams in each group.

Table 13—Results of tension tests on end-jointedYellow Poplar tension lamination material(lognormal distribution)

Property 2 by 4 2 by 6 2 by 8 Combined

Sample size 29 30 30 89Specific gravity 0.49 0.47 0.46 0.47Moisture content (%) 8.8 9.9 9.1 9.3Average tensile 6,770 7,050 5,220 6,160

strength (lb/in2)COV tensile 22.7 31.2 12.2 25.4

strength (%)X0.05 at 75% 4,230 3,640 4,100 3,840

tolerance

Table 14—Results of bending tests on glulam beams

Laminations

Figure 3—Loading configuration for full-size beam bendingtests.

During application of load, beam deflections were mea-sured using a precision ruler (0.02 in.) that was at-tached to the beam. Deflections were recorded at mid-depth with respect to a string line attached over eachsupport. Preliminary tests were conducted by loadingthe beams within the design level to check for consis-tency in the rate of loading and deflection measure-ments. The readings were taken at specified load incre-ments with the use of a surveyor’s scope; this allowedthe recorder to take readings to the nearest 0.01 in.

After the beams failed, detailed descriptions of the fail-ure propagations were recorded, along with an assess-ment of the cause of failure (e.g., end joint, knot). Eachbeam failure was photographed for future reference.The MOR and MOE values were calculated using stan-dard flexural formulas. Dead load stress was includedin the MOR calculations. The MOE values were cal-culated based on the slope of the load-deflection curvedetermined by a regression of the readings up to designload.

End JointsEnd-jointed lumber specimens from each grade and sizewere also evaluated. The test specimens were about8 ft long with the end joint located near midspan.Prior to testing, specimens were face- and edge-planedto the same dimensions of the laminating lumber used

Property 8 12 17

Sample size 15 15 15Moisture content (%) 8.2 7.5 8.0

Normal distributionAverage MOR (1b/in2)COV of MOR (%)MOR0.05 75th percentileAverage MOE (× 106 lb/in2)COV of MOE (%)

8,050 7,560 6,56016.8 15.9 17.8

5,360 5,170 4,2421.89 1.94 1.794.45 3.25 3.35

Lognormal distributionAverage MOR (lb/in2)COV of MOR (%)MOR0.05 75th percentile

8,060 7,560 6,57017.3 16.1 18.0

5,640 5,440 4,530

in the glulam beams and stored in a conditioning room.The specimens were stored for approximately 30 daysin temperature and humidity conditions that equi-librated the moisture content level of the lumber toabout 12 percent. The loading configuration for theend-jointed lumber tension tests was that specified byAITC T119 (1992); however, the time-to-failure wastargeted at 5 to 10 min.

The specimens were tested to failure in tension accord-ing to the procedures in ASTM D198 (1992b), whichspecify a time-to-failure of approximately 5 to 10 min.Quality control practices for testing end joints wouldnormally follow AITC 119 (1992), which specify a time-to-failure of 2 min. The end joints in this researchproject were tested according to ASTM D198 to corre-spond to the failure times of the full-sized beams. Theunrestrained distance between the grips of the tensionmachine was 30 in., the minimum span of the machine.These data provided information to relate the perfor-mance of the individual end joints to that in the beams.

Strength and Stiffness

Bending test results on the beams are summarized inTable 14; individual end-joint results are given in Ap-pendix B. Figure 4 compares the cumulative distribu-tion function (CDF) of MOR for the 8-, 12-, and 17-lamination beams.

BeamsMost beam failures were catastrophic; localized fail-ures emitted cracking sounds as the ultimate loadwas approached. Several beams exhibited compres-sion wrinkling at or between the load points prior to

9

Figure 4—Empirical cumulative distribution function of MORfor Yellow Poplar glulam beams.

Table 15—Estimated initial cause ofglulam beam failure

Number ofbeam

laminations

Failure type 8 12 17

Compression followed 1 3 3by tension

Tension in strength- 3 6 3reducing characteristic

Tension in clear lumber 0 0 2Tension in end joint 11 6 7

maximum load. All beams ruptured throughoutthe tension zone near or within the constant mo-ment region. Although it was not possible topositively identify the initial point of failure forall beams, estimates were made of the trigger-ing mechanism of the initial cause of failure.These results are summarized in Table 15. De-tailed descriptions of beam failures are provided inAppendix B.

As expected, most beams failed through either an endjoint or a strength-reducing characteristic (knot orgrain deviation) in the highly stressed regions of thebeams, and subsequently propagated through the slope-of-grain characteristics in the lumber. An abrupt orbrash failure of the lumber was observed on some occa-sions in lumber possessing mineral-stain characteristics.This type of mineral stain failure was not associatedwith a marked weakness in either the beams or lumber.The failure of several beams propagated near gluelineswith shallow failure, but this was not necessarily asso-ciated with low-strength beams and was not believed tobe a cause of failure.

10

Figure 5—Empirical cumulative distribution function of tensilestrength for end-jointed tension lamination lumber.

End JointsResults of tension tests on the end-jointed tension lam-ination material are given in Table 13 and shown inFigure 5. Test results on the remaining grades of endjoints (2.0–1/6, 2.0–1/3, 1.8–1/3, and No. 2) are inAppendix A.

Although a high percentage (>50 percent) of beam fail-ures reported in Table 15 were due to end joints, thisdoes not indicate that the end-joint quality was poor.The only requirement for end-joint performance is thatthe 5th percentile of tensile strength (75 percent tol-erance) be at a qualification level that is 1.67 timesthe target design of the glulam beams (ANSI 1992).The desired qualification level for the end joints inthis study was 1.67 × 2,400 lb/in2, which is approx-imately 4,010 lb/in2. The results in Table 13 showthat the 2 by 4 and 2 by 8 end-jointed lumber metthis criterion (4,230 and 4,100 lb/in2, respectively),and the 2 by 6 results were slightly less than the tar-get level (3,640 lb/in2). Note that the variability of the2 by 6 end-joint strength results (Table 13) was nearlytwice that observed for the 2 by 4 and 2 by 8 results;this higher variability resulted in a lower calculated5th percentile. Also, the average end-joint strengthof the 2 by 6’s was slightly greater than that of the2 by 4’s, which indicates that the 2 by 6 end jointsperformed at a level nearly equal to that of the 2 by4 end joints (except for variability). It is suspectedthat the procedures used in manufacturing the 2 by 6group to obtain “matched” sets with a range of qual-ities significantly influenced the variability of the testresults. When all end-joint tensile strength results werecombined, the qualification level equaled 3,840 lb/in2,which was slightly less than the target of 4,010 lb/in2,again being influenced by the variability of the 2 by 6group. However, combining only the 2 by 4 and 2 by 8groups gave a qualification level of 3,940 lb/in2.

Analysis

Values of the 5th percentiles given in Tables 13 and14 were calculated assuming both the normal and log-normal distributions. However, to conduct an anal-ysis of the data, ASTM D3737 (1992a) recommendsthat a lognormal distribution be used. Therefore, theanalysis conducted in this section assumes a lognormaldistribution.

Beam Size

By evaluating three beam sizes, it was possible to studythe effect of volume on the strength of Yellow Poplarglulam beams. Results indicated that the calculatedbending strength values decreased as the beam volumeincreased (Table 14).

The following relationship has been used to account forthe effect of varying beam size on strength for otherspecies (Moody and others 1988):

(1)

where

b = beam width (in.)

d = beam depth (in.)

= beam length (ft)

Cv = volume effect factor

and x, y, and z are exponents that determine therelative adjustments for width, depth, and length,respectively.

When width, depth, and length are combined to obtainvolume, the following relationship is used in place ofEquation (1) (assuming x = y = z).

(2)

where

V0 = standard volume (5.125 in. by 12 in. by 21 ft)

V = volume of actual beam

k = exponent that represents x = y = z

Results have shown that exponents of about x = y = z= 1/10 adequately explain the variation in strength forDouglas Fir glulam beams (Moody and others 1990).For red maple glulam beams (Manbeck and others1993), an exponent of 0.071 was found. A volume ef-fect equation by ASTM D07 adopted x = y = z =1/10. In contrast, AITC adopted x = y = z = 1/10 for

all species of glulam except Southern Pine, for whichAITC adopted x = y = z = 1/20 (AITC 1991).

In our study, to determine the most appropriatemethod of accounting for variation in beam strengthas a result of beam size, a confidence interval on theratio of the beam sizes was conducted. First, the ratiobetween the volume effect factors of each beam size wasdetermined using both 1/10 and 1/20. Next, the ratiobetween the averages of the various paired groupings ofbeams was determined along with a confidence intervalusing the procedures described by Wolfe and Moody(1978). Table 16 lists the results of this analysis. Theseresults indicate that neither exponent can be rejectedbecause predicted results using both exponents werewithin the confidence interval. When comparing the 17-lamination beams with the 8- and 12-lamination beams,the predicted results with 1/20 were at the edge of theconfidence interval, whereas those with 1/10 were nearthe middle of the confidence interval.

Next, a regression analysis was conducted to determinethe exponent that best fit all data. This exponent was0.088 (1/11.4) and is shown with the bending strengthdata in Figure 6. This result agrees closely with thevalue of 0.071 (1/14.1) reported for red maple glulamtimber (Manbeck and others 1993). In all further anal-ysis, the exponent 0.088 was used to adjust data to acommon size.

Design Levels

The strength level of all beams was adjusted to a stan-dard beam size of 5-1/8 by 12 in. by 21 ft, using thebest fit volume effect relationship (0.088 exponent).Then, results were pooled and analyzed to deter-mine the appropriate design level using ASTM D2915(1992c). A lognormal distribution was assumed, andthe tolerance limit (75 percent confidence in 5th per-centile) was adjusted by dividing by 2.1 to obtainthe design level. Figure 7 shows that the data closelyfit the assumed lognormal distribution. Results inTable 17 indicate that the calculated design level of2,650 lb/in2 exceeded the target level of 2,400 lb/in2.Calculating each beam group individually, the resultingdesign level values were 2,520, 2,730, and 2,470 lb/in2

for the 8-, 12-, and 17-lamination beams, respectively(also Table 18).

Table 14 shows that the average MOE of the 8- and12-lamination beams exceeded the target level of1.8 × 106 lb/in2 (1.89 and 1.94 × 106 lb/in2, respec-tively). Also, the 17-lamination beams averaged slightlyless (1.79 × 106 lb/in2) as a result of the low stiff-ness of the 1.8-1/3 grade (1.69 × 106 lb/in2 (Table 9).However, all three beam sizes rounded to at least thetarget MOE level of 1.8 × 106 lb/in2. As expected with

11

Table 16—Analysis of volume effect factor

Mean MOR ratioVolume effect exponent

Lamination Actual (90% confi-comparison x = y = z = 0.1 x = y = z = 0.05 dence interval)

12 to 8 0.876 0.935 0.939 (0.841, 1.037)17 to 8 0.798 0.893 0.815 (0.725, 0.905)17 to 12 0.911 0.955 0.868 (0.772, 0.964)

Table 17—Glulam beam bending strength results adjusted to standarddimensions of 5-1/8 in. wide by 12 in. deep by 21 ft long

AverageSample M O R C O V 5th percentile Adjusted 5%

Beam group size (1b / in 2 ) ( % ) (75% tolerance limit) tolerance limit

8-Lam 15 8,060 17.3 5,640 2,52012-Lam 15 7,560 16.1 5,440 2,73017-Lam 15 6,560 18.0 4,530 2,470

All 45 7,680 18.0 5,570 2,650

the use of E-rated lumber in glulam, the variability ofbeam MOE was quite low (Table 14).

Comparison With Predicted Values

StrengthThe actual lumber MOE values from Table 9, the ac-tual knot properties from Table 10, and the tensionlamination criteria from Table 6 were used to reana-lyze the three glulam combinations shown in Figure 1with ASTM D3737 (1992a) procedures. The reanaly-sis of the 8-, 12-, and 17-lamination combinations gaveallowable design bending values for the glulam beamsof 3,000, 2,600, and 2,600 lb/in2, respectively, whencompared to the allowable design bending values cal-culated from the actual beam tests of 2,520, 2,730, and2,470 lb/in2, respectively.

An additional comparison was made of the tensilestrength performance of the tension lamination qual-ity end joints. The 5th percentile results of each end-joint group (Table 13) were divided by the 1.67 qual-ification factor from ANSI A190.1 (1992) to deter-mine the design level for each group. The results in-dicated that the joints would meet levels of 2,530,2,180, and 2,460 lb/ in2 for the 2 by 4, 2 by 6, and2 by 8 end-jointed lumber specimens, respectively. Thisanalysis, in addition to the observations from Table 15,indicates that the beam performance levels were con-

12

trolled by end-joint strength. Although the tensilestrength of the 2 by 6 end joints did not meet the tar-geted 2,400 lb/in2 (p .rimarily as a result of high vari-ability of the results, Table 13), the performance of the12-lamination beams met a design level of 2,700 lb/in2.Also, as previously discussed, the average performanceof the 2 by 6 end joints was similar to that of the2 by 4 end joints. Therefore, an argument could bemade that the 2,150 lb/ in2 end-joint design qualifica-tion level for the 2 by 6 end joints would have beenconsiderably greater if a variability problem had notbeen present. As previously discussed, the cause of theincreased variability of the 2 by 6 tension laminationquality end-joint group was probably the method inwhich this group was gathered. It could also be arguedthat this sample group was not representative, but stillwithin grade limitations, of the end joints used in thebeams.

The analysis discussed in this section was com-piled (Table 18) to closely inspect the relation-ship between actual and predicted beam perfor-mance and end-joint performance. Table 18 showsthat for the 8- and 17-lamination beam groups,end-joint performance was the controlling factor ofthe predicted beam design levels. Also, the actualperformance of these two beam groups was at thelevels expected, equivalent to the design levels ofthe end joints. In contrast, for the 12-laminationgroup, ASTM D3737 predictions were slightly less

Figure 6—Variation in beam MOR with beam volume showinga line approximating an exponent of 0.088 for Equation (1).

Figure 7—Histogram of MOR values adjusted to a standardbeam size and compared to a fitted lognormal distribution.

(conservative) than the actual beam performance. Thequestion remains as to the variability of the tested endjoints. However, note that the mean tensile strengthvalue of the 2 by 6 end joints was 7,050 lb/in2, whichwas greater than the 6,770 lb/in2 strength of the2 by 4 end joints. If the 2 by 6 end-joint group hada coefficient of variation of 18 percent, keeping boththe same sample size and mean, the resulting end-jointqualification level would be 2,800 lb/in2, which is close

Table 18—Results of calculated design levelsof full-sized glulam beams and end-jointedlumber

Design level (lb/in2)

End-jointBeam group Predicteda qualification Calculatedb

8-Lam 3 , 0 0 012-Lam 2 , 6 0 017-Lam 2 , 6 0 0

a Using ASTM D3737.b From actual tests.

2 , 5 3 0 2 , 5 2 02 , 1 8 0 2 , 7 3 02 , 4 6 0 2 , 4 7 0

to the beam performance of 2,730 lb/in2. Although afirm conclusion cannot be made based on this hypo-thetical situation, this observation of the 2 by 6 end-joint group did not contradict expected results. Basedon the reanalysis using actual lumber properties andthe beam test results, it appears that ASTM D3737and ANSI A190.1 procedures adequately establishedthe performance of the Yellow Poplar glulam beamsand end joints. Thus, both analyses justify a designbending stress of more than 2,400 lb/in2.

StiffnessBeam stiffness can be predicted by using the actualMOE values from the lumber used in beam manufac-ture and the transformed section method of ASTMD3737. The MOE values were predicted for eachbeam, and the results are shown in Figure 8. The1:1 ratio line is included to show that the actualbeam MOE values slightly exceeded the predictedvalues, and the horizontal line shows that the ma-jority of the actual beam MOE values exceeded thetargeted MOE level of 1.8 × 106 lb/in2. In additionto analyzing beam MOE performance individually,the actual to predicted MOE ratios were calculatedfor each beam group (Table 19). The results fromFigure 8 and Table 19 indicate that the proposed beamcombinations (Fig. 1) will meet or exceed the targetMOE level of 1.8 × 106 lb/in2 and that ASTM D3737procedures adequately predict Yellow Poplar glulamMOE.

13

Figure 8—Relationship between actual MOE determined bytests and predicted MOE calculated from lumber properties.

Table 19—Comparison of actual and predictedMOE values based on actual lumber properties

Beamgroup

MOE(× 106 lb/in2)

A / PActual Predicted difference

(A) (P) A / P (%)

8-Lam 1.89 1.83 1.03 3.212-Lam 1.94 1.88 1.03 3.117-Lam 1.79 1.80 0.99 0.1

Conclusions

Based on the evaluation and analysis of 45 YellowPoplar glulam beams, a bending stress of 2,400 lb/in2

and design MOE of 1.8 × 106 lb/in2 are obtainable andmake this species a feasible candidate for structuralglulam construction, providing the following criteria aremet.

The outer 10 percent of the laminations (topand bottom) are E-rated to have an MOE of2.0 × 106 lb/in2.

The next inner 10 percent of the laminations(top and bottom) are E-rated to have an MOE of1.8 × 106 lb/in2.

The bottom (tension) 2.0E laminations are visuallysorted for a maximum allowable edge knot of one-sixth the cross section.

The top (compression) 2.0E laminations are visuallysorted for a maximum allowable edge knot of one-third the cross section.

All 1.8E laminations (top and bottom) are visuallysorted for a maximum allowable edge knot of one-third the cross section.

The end-joint qualifications follow procedures recom-mended in ANSI A190.1.

Tension lamination grading criteria in Table 6 areused.

In addition, we conclude that ASTM D3737 adequatelypredicts the strength and stiffness performance ofYellow Poplar glulam timber, given the actual prop-erties of the constituent lumber.

References

14

Appendix A-Tension Test Results Table 20—Properties and quality of 2 by 4’s usedin tension lamination

Appendix A contains the following: Relative

l Properties and quality of tension laminations follow-ing the relative rating system in Table 11.

l Results of tension tests on end-jointed lumber for the

MOE quality ofBeam MC (x106 midlengthnumber (%) lb/in2) Characteristica region

2.0-1/6, the combined 1/3 edge knot, and the No. 2grades of lumber.

YP4-1

YP4-2

YP4-3

YP4-4

YP4-5

YP4-6

YP4-7

YP4-8

YP4-9

YP4-10

YP4-11 9 2.31

YP4-12

YP4-13

YP4-14

10 2.0010 2.01

9 1.73

9 2.04

YP4-15

9 2.019 1.92

8 2.06

8 2.08

8 1.92

9 2.01

9 1.78

9 2.029 2.06

? 2.019 2.12

8 1.948 2.17

12 1.82

10 2.02

7 2.27

8 2.13

7 1.98

8 1.869 2.12

Clear45% GD

30% center GD

45% GD and1:12 SOG

50% EK + GD(both sides), and15% GD (oneside)

50% CK + GD(one side)

Clear

ClearClear

Clear40% GD (one

side)

ClearClear

Clear

33% GD (bothsides)

Clear

1:14 SOG, <15%EK + GD and50% CK + GD

<15% EK + GD(one side)

1:12 SOGClear

25% EK + GD

30% GD (oneside)

Clear

Clear20% GD (one

side)

Low

Medium

Low

Low

High

Low

High

High

Medium

Low

High

Low

Medium

Medium

Medium

a CK, center knot; GD, grain deviation;SOG, slope of grain; EK, edge knot.

16

Table 21—Properties and quality of 2 by 6’s used Table 22—Properties and quality of 2 by 8’s usedin tension lamination in tension lamination

Relative RelativeMOE quality of MOE quality of

Beam MC (x106 midlength Beam MC (x106

(%) lb/in2) Characteristicsamidlength

number region number (%) lb/in2) Characteristicsa region

YP6-1 Low

YP6-2

YP6-3

YP6-4

YP6-5

YP6-6

YP6-7

9 2.04

8 2.287 2.25

7 1.887 1.87

7 2.19

YP6-8 9 2.07

YP6-9

YP6-10

YP6-11 8 1.99

YP6-12 7 1.99

YP6-13 10 1.99

YP6-14 8 2.169 2.04

YP6-15

7 2.00

810

8

1.882.11

2.08

7 1.73

15% CK + GD(one side)

<15% CK + GD1:18 edge SOG

<10% CK + GD(one side)

<20% CK + GD(one side)

Clear

<20% CK + GDClear

1:18 SOGClear

5% CK + GD,1:10 SOG

7 2.18

20% GD (bothsides)

1:16 SOG, <10%edge GD

8 1.90 1:16 SOG (face),

10 2.118 2.14

79

2.011.93

and <15% CK +GD (one side)

Clear High10% GD (one

side)

Clear High

<10% GD High

<10% CK + GD High(one side)

Clear Medium20% CK + GD

(both sides)

1:16 edge SOG Low1:16 face SOG

Medium YP8-1

Medium YP8-2

High YP8-3

High YP8-4

YP8-5High

Medium YP8-6

Low

Low

Low

YP8-7

YP8-8

YP8-9

YP8-10


YP8-11

YP8-12

YP8-13

YPS-14

YP8-15

6 2.299 1.81

8 1.998 1.97

7 1.838 1.67

20% CK + GD35% CK + GD

Clear20% CK + GD

ClearClear

8 2.169 1.96

910

8

1.922.092.10

25% CK + GD20% CK + GD

ClearClearClear

8 2.059 2.15

9 2.177 1.68

7 2.1510 2.11

20% CK + GD30% CK + GD

ClearClear + lo MOE

ClearClear

10 2.31 Clear7 2.25 Clear

108

1.801.75

10 1.808 1.71

10 1.94

Clear25% CK + GD

25% CK + GDClearClear

8 1.74 20% CK + GD

8 2.27 Clear10 1.89 Clear

7 2.06 Clear

1010

98

1.92 Clear1.97 <10% CK + GD

1.81 >20% CK + GD2.11 Clear

Medium

High

Low

High

Low

Medium

High

High

Low

Low

Medium

High

High

Low


17

Table 23—Results of subsequent tension tests on Yellow Poplar end-jointed lumber using lognormal distribution

Beam gradeand property

Lumber size All sizescom-

2 by 4 2 by 6 2 by 8 bined

2.0-1/6 grade

All specimens

Sample size 53 17 49Average tensile 6,630 5,560 5,010

strength (TS)(lb/in2)

COV TS (%)TS0.05 (50%)

(lb/in2)TS0.05 (75%)

(lb/in2)Specific gravityMoisture con-

tent (%)

20.3 31.3 24.54,570 3,060 3,170

4,430 2,780 3,050

0.48 0.47 0.468.9 10.2 9.3

Specimens withEJ failure

Sample sizeAverage TS

(lb/in2)COV TS (%)TS0.05 (50%)

(lb/in2)TS0.05 (75%)

(1b/in2)

1/3 EK gradea

All specimens


(lb/in2)COV TS (%)TS0.05 (50%)

(1b/in2)TS0.05 (75%)


tent (%)

45 13 466,760 5,830 5,080

14.9 24.8 22.15,180 3,680 3,380

5,040 3,350 3,260

5 14 55,750 4,740 4,420

54.9 22.2 21.01,900 3,150 3,010

1,250 2,910 2,540

0.47 0.47 0.479.2 10.0 9.8

1195,870

27.83,480

3,380

0.479.3

1045,970

24.63,780

3,680

244,810

29.12,780

2,600

0.479.7

Beam gradeand property

Lumber size All sizescom-

2 by 4 2 by 6 2 by 8 bined

1/3 EK gradea —con.



(lb/in2)COV TS (%)TS0.05 (50%)

(lb/in2)TS0.05 (75%)

(lb/in2)

No. 2 gradeAll specimens


(lb/in2)COV TS (%)TS0.05 (50%)

(1b/in2)TS0.05 (75%)


tent (%)



(lb/in2)COV TS (%)TSo.05 (50%)

(lb/in2)TS0.05 (75%)

(lb/in2)

4 11 45,930 5,000 4,640

32.8 21.1 19.83,160 3,400 3,240

2,270 3,110 2,640

5 10 75,920 4,880 5,200

20.8 28.9 63.44,050 2,830 1,430

3,420 2,490 1,000

0.47 0.49 0.468.9 10.2 9.5

4 7 65,610 5,130 5,240

20.0 21.1 69.03,890 3,480 1,270

3,170 3,070 830

195,090

23.03,330

3,110

223,840

42.21,670

1,500

0.489.6

175,350

44.22,240

1,950

aBecause of the small sample sizes, results for 2.0-1/3 and 1.8-1/3 grades were combined.

18

Appendix B—Glulam Beam Resultsand Failure Descriptions

Appendix B contains the following:

l Tables listing the results of the physical properties(dimension, moisture content, and weight), mechan-ical properties (stiffness and strength), and descrip-tions of the failures for each beam.

l Beam failure maps.

19

Tab

le 2

4—R

esul

ts o

f be

ndin

g te

sts

on 2

0-ft

(19

-ft

span

) Y

ello

w P

opla

r be

ams

Bea

mW

idth

Dep

th

MC

(%)

YP

4-1

10.8

88

164

4:30

6,90

05,

320

1.98

YP

4-2

10.8

88

164

8:20

11,9

009,

120

1.81

YP

4-3

10.8

88

162

5:26

9,50

07,

300

1.91

YP

4-4

10.8

88

162

4:57

8,76

06,

730

1.84

YP

4-5

10.8

87

164

6:47

11,3

408,

700

1.89

YP

4-6

10.8

87

164

6:42

10,9

608,

410

1.97

YP

4-7

10.8

87

162

7:31

12,4

409,

530

1.96

YP

4-8

3.00

3.00

3.00

3.00

3.00

3.00

3.00

3.00

3.00

3.00

3.00

3.00

3.00

3.00

3.00

10.8

87

164

7:00

11,0

808,

500

1.83

YP

4-9

10.8

010

160

4:07

8,90

06,

930

YP

4-1

010

.88

816

05:

25

YP

4-11

10.8

88

164

8:O

1

YP

4-12

10.8

89

164

7:56

YP

4-1

3

YP

4-14

YP

4-15

10.8

88

162

6:50

10.8

8

10.8

8

Dim

ensi

on (

in.)

Tim

e t

o L

oa

d a

t

wei

ght

(lb)

10 8

160

164

Bea

mB

eam

EJ

inA

ny E

J

fail

ure

fail

ure

MO

Ra

MO

E

TL

bF

ail

(min

:s)

(lb

) (1

b/i

n2

) (l

b/i

n2

) (Y

/N)

(Y/N

)C

om

men

t

5:00

5:00

10,9

00

14,4

00

9,40

0

11,0

00

10,4

00

9,40

0

8,36

0

11,0

30

7,22

0

8,44

0

7,98

0

7,22

0

2.01

1.91

1.97

1.75

1.75

1.83

1.90

Y N Y Y Y Y Y N Y N N Y N Y Y

Y Y Y Y Y Y Y Y Y Y N Y Y Y Y

Fai

led

in

tens

ion

lam

inat

ion

(TL

) en

d jo

int

(EJ)

(1

00%

) at

10

.5

ft,

prop

agat

ed

thro

ugh

2d

lam

inat

ion.

Fai

led

at

TL

-EJ

(50%

) at

14

.5

ft,

thro

ugh

30%

gr

ain

devi

atio

n (G

D)

in T

L a

t 10

.7 f

t.

Fai

led

in T

L-E

J (1

00%

) at

9.8

ft

thro

ugh

EJ

in 3

d la

min

atio

n(1

00%

) at

11

ft.

Fai

led

in T

L-E

J 10

0%)

at 1

3 ft

, th

roug

h E

J in

2d

lam

inat

ion

(20%

)at

18

ft

, th

roug

h E

J in

3d

la

min

atio

n (2

5%)

at

13.2

ft

.

Fai

led

in

TL

-EJ

(100

%)

at

10

ft,

thro

ugh

EJ

in

2d

lam

inat

ion

(25%

)at

12

.7

ft,

thro

ugh

3d

lam

inat

ion.

Fai

led

thro

ugh

TL

-EJ

7.5

ft,

thr

ough

E

J i

n 2

d(100

%)

at 7

ft,

thr

ough

40%

EK

+ G

D a

tla

min

atio

n (8

0%)

at

11.7

ft

, th

roug

h E

J in

3d

lam

inat

ion

(25%

) at

13

.2

ft.

Fai

led

in T

L-E

J (1

00%

) at

11.

2 ft

, th

roug

h E

J in

2d

lam

inat

ion

(50%

) at

4.5

ft.

Fai

led

alon

g 1:

20

slop

e-of

-gra

in

(SO

G)

in

TL

at

8

ft-1

2 ft

, th

roug

hE

J in

2d

la

min

atio

n (8

0%)

at

9.4

ft,

thro

ugh

EJ

in

3d

lam

inat

ion

(100

%)

at

10.5

ft

, th

roug

h E

J in

3d

la

min

atio

n (2

0%)

at

12.5

ft

.

Fai

led

in

TL

-EJ

(100

%)

at

13

ft,

thro

ugh

EJ

in

2d

lam

inat

ion

(10%

)at

15

ft.

2d

lam

inat

ion

(100

%)

at

15

ft,

thro

ugh

EJ

in

3d

lam

inat

ion

(50%

)Fa

iled

in

TL

th

roug

h 50

%

CK

+

G

D

at

15

ft,

thro

ugh

EJ

in

at 1

0.7

ft.

Com

pres

sion

wri

nkli

ng t

hrou

gh t

op t

hree

lam

inat

ions

at

11.2

ft,

TL

sliv

er f

rom

9 t

o 13

ft

at f

ailu

re.

Fai

led

in

TL

-EJ

(75%

) at

12

ft

, th

roug

h E

J in

2d

la

min

atio

n (1

5%)

at

14

ft,

thro

ugh

glue

line

be

twee

n 2d

an

d 3d

la

min

atio

ns.

Fai

led

in

TL

th

roug

h 25

%

EK

+

G

D

at

11

ft,

thro

ugh

EJ

in2d

la

min

atio

n (2

0%)

at

9.5

ft,

thro

ugh

EJ

in

3d

lam

inat

ion

(100

%)

at 7

.2 f

t.

Fai

led

in

TL

-EJ

(100

%)

at

13

ft,

thro

ugh

EJ

in

2d

lam

inat

ion

(10%

)at

9 f

t.

Fai

led

in T

L-E

J (1

00%

) at

8.2

ft,

thr

ough

EJ

in 2

d la

min

atio

n(2

5%)

at

12

ft,

thro

ugh

glue

line

be

twee

n 2d

an

d 3d

la

min

atio

ns.

aM

OR

ca

lcul

atio

ns

incl

ude

dead

lo

ad

stre

ss.

bE

J in

th

e T

Lw

ithi

n th

e >

85%

m

axim

um

mom

ent

regi

on.

Tab

le 2

5—R

esul

ts o

f be

ndin

g te

sts

on 3

0-ft

(28

.5-f

t sp

an)

Yel

low

Pop

lar

beam

s

Bea

m

Dim

ensi

on

(i

n.)

T

ime

to

Lo

ad

atB

eam

Bea

mE

J in

Any

EJ

MC

wei

ght

fail

ure

fail

ure

MO

Ra

MO

E

TL

bF

ail

Wid

th

De

pth

(%)

(lb)

(min

:s)

(lb

) (1

b/i

n2

) (l

b/i

n2

) (Y

/N)

(Y/N

)C

om

men

t

YP

6-1

YP

6-2

YP

6-3

YP

6-4

YP

6-5

YP

6-6

YP

6-7

YP

6-8

YP

6-9

YP

6-1

0

YP

6-11

YP

6-1

2

YP

6-1

3

YP

6-1

4

YP

6-1

5

4.94

4.94

4.94

4.94

4.94

4.94

4.94

4.94

4.94

4.94

4.94

4.94

4.94

4.94

4.94

16.4

47

592

6:32

26,7

408,

220

2.02

16.4

48

592

6:54

28,5

208,

760

1.99

16.4

47

586

10:3

029

,540

9,06

01.

94

16.4

47

592

6:32

22,7

607,

010

1.91

16.4

48

586

7:20

25,6

007,

870

1.98

16.4

47

584

5:22

20,7

606,

400

1.93

16.4

48

594

6:56

21,4

906,

620

2.00

16.4

47

592

8:l

l26

,400

8,11

01.

87

16.4

47

592

5:58

22,7

307,

000

1.85

16.4

48

592

9:08

30,7

209,

420

2.08

16.4

48

588

5:53

20,0

806,

190

16.4

48

596

10:3

029

,600

9,08

0

16.4

48

9:14

7,66

0

16.4

46:

565,

850

16.4

4

7 7

594

594

592

5:30

24,9

10

18,9

50

19,6

006,

110

1.91

1.92

1.89

1.87

1.97

N Y N Y Y Y N Y N Y N N N Y Y

Y Y Y Y Y N Y Y Y Y Y N N Y Y

Com

pres

sion

wri

nkli

ng t

hrou

gh t

op t

wo

lam

inat

ions

at

13.5

ft

(EJ—

top

lam

inat

ion)

, fa

iled

in

TL

thro

ug

h 1

5%

CK

+ G

D a

t 1

2.8

ft,

thro

ugh

EJ

in

2d

lam

inat

ion

(100

%)

at

13.5

ft

, th

roug

h E

J in

5th

lam

inat

ion

(100

%)

at

13.5

ft

.

Fai

led

in

TL

th

roug

h 12

.5%

C

K

+

GD

at

16

ft

, th

roug

h E

J in

3d

lam

inat

ion

(100

%)

at

12.5

ft

.

Com

pres

sion

w

rink

ling

in

to

p la

min

atio

n at

13

ft

, fa

iled

th

roug

h T

Lto

E

J in

2d

la

min

atio

n (3

0%)

at

14.8

ft

, th

roug

h E

J in

5t

h la

min

a-ti

on

(100

%)

at

18

ft,

thro

ugh

EJ

in

6th

lam

inat

ion

(40%

) at

15

.5

ft.

Com

pres

sion

w

rink

ling

in

to

p la

min

atio

n at

18

.2

ft,

fail

ed

thro

ugh

TL

-EJ

(10

%)

at 2

3.3

ft,

th

rou

gh

EJ

in 3

d l

amin

atio

n (

10

0%

) at

18 f

t.

Fai

led

in

TL

-EJ

(100

%)

at

14

ft,

thro

ugh

EJs

in

2d

la

min

atio

n (2

5%ea

ch)

at

9.3

ft

and

15.7

ft

, th

roug

h E

J in

3d

la

min

atio

n (1

00%

) at

13.7

ft

.

Fai

led

thro

ugh

1:18

S

OG

in

T

L

at

9 to

13

ft

, br

ash

lum

ber

fail

ure

in2d

la

min

atio

n at

9

ft.

Fai

led

thro

ugh

1:10

S

OG

in

T

L

at

16

to

18

ft,

thro

ugh

EJ

in2d

la

min

atio

n (2

5%)

at

14.8

ft

, th

roug

h gl

ueli

ne

betw

een

2d

and

3d

lam

inat

ions

fr

om

11

ft

to

21

ft.

Fai

led

at b

oth

TL

-EJs

(50

% e

ach)

at

10 f

t an

d 23

.3 f

t, t

hrou

gh E

Jin

2d

la

min

atio

n (1

00%

) at

16

.8

ft,

thro

ugh

3d

lam

inat

ion.

Fai

led

in

TL

th

roug

h 12

.5%

C

K

+

GD

at

16

.5

ft,

thro

ugh

EJ

in2d

la

min

atio

n (1

00%

) at

15

.5

ft,

thro

ugh

glue

line

be

twee

n 2d

an

d3d

la

min

atio

ns

from

12

to

22

ft

.

Fai

led

in T

L-E

J (8

0% a

t 9.

5 ft

, th

roug

h 2

EJs

in

3d l

amin

atio

n(1

00%

ea

ch)

at

10

and

17

ft.

Fai

led

in T

L-E

J (3

0%)

at 8

.5 f

t, t

hrou

gh 2

d an

d 3d

lam

inat

ions

.

Fai

led

in T

L t

hrou

gh <

10%

CK

+ G

D a

t 19

.5 f

t, t

hrou

gh 5

th l

ami-

nat

ion

.

Fai

led

in

TL

th

roug

h 7.

5%

CK

+

G

D

at

15

ft,

thro

ugh

3d

lam

ina-

tion

.

Fai

led

in T

L-E

J (1

00%

) at

17

ft,

thro

ugh

2d l

amin

atio

n.

Fai

led

in T

L-E

J (1

00%

) at

14.

7 ft

, th

roug

h E

J in

2d

lam

inat

ion

(90%

) at

15

.8

ft,

thro

ugh

glue

line

be

twee

n 2d

an

d 3d

la

min

atio

ns.

a MO

R

calc

ulat

ions

in

clud

e de

ad

load

st

ress

.b

EJ

in

the

TL

wit

hin

the

>85

%

max

imum

m

omen

t re

gion

.

Tab

le 2

6—R

esul

ts o

f be

ndin

g te

sts

on 4

0-ft

(38

-ft

span

) Y

ello

w P

opla

r be

ams

Dim

ensi

on

(i

n.)

T

ime

toL

oad

atB

eam

Bea

mE

J in

MC

(%)

TL

b

(Y/N

)F

ail

(Y/N

)B

eam

Wid

thD

epth

wei

ght

fail

ure

fail

ure

MO

Ra

(lb)

(min

:s)

(lb

) (l

b/i

n2

)

YP

8-1

6.75

23.3

88

1,47

49:

5860

,780

9,02

0

Any

EJ

MO

E(l

b/i

n2)

1.77

YP

8-2

6.75

23.3

88

1.47

25:

0034

,480

5,17

01.

79

YP

8-3

6.75

23.3

89

1,47

25:

4537

,580

5,62

01.

72

YP

8-4

6.75

23.3

89

1,47

47:

3538

,780

5,80

01.

80

YP

8-5

6.75

23.3

88

1,47

48:

0547

,540

7,08

01.

76

YP

8-6

6.75

23.3

88

1,46

88:

0848

,180

7,17

01.

83

YP

8-7

6.75

23.3

88

1,47

28:

3235

,940

5,38

01.

69

YP

8-8

6.75

23.3

89

1,47

68:

3247

,900

7,13

01.

90

YP

8-9

6.75

23.3

89

1,47

29:

0548

,120

7,16

01.

92

YP

8-1

06.

7523

.38

81,

476

8:15

52,8

407,

850

1.82

YP

8-11

6.75

23.3

88

1,47

07:

4546

,780

6,97

01.

79

YP

8-1

26.

7523

.38

81,

474

6:08

46,4

206,

910

1.78

YP

8-1

36.

7523

.38

81,

464

7:35

32,1

20

YP

8-14

6.75

23.3

87

1,47

28:

5047

,380

YP

8-1

56.

7523

.38

81,

470

7:35

35,3

80

4,82

0

7,05

0

5,30

0

1.76

1.77

1.77

Co

mm

ent

Y Y Y Y Y Y Y N Y Y Y N Y Y Y

Y Y Y Y Y Y Y Y Y Y Y Y Y N Y

Com

pres

sion

w

rink

ling

in

to

p tw

o la

min

atio

ns

at

load

po

ints

(1

6 ft

and

24

ft),

fa

iled

at

T

L-E

J (1

00%

) at

13

ft

, th

roug

h E

J in

2d

la

mi-

nati

on

(100

%)

at

15

ft.

Fai

led

in

TL

th

roug

h 20

%

CK

+

G

D

at

27

ft.

thro

ugh

EJ

in

2dla

min

at.i

on

(100

%)

at

24.5

ft

, th

roug

h E

J in

4t

h la

min

atio

n (9

0%)

at23

ft.

Fai

led

in

TL

th

roug

h lo

w

MO

E

boar

d fr

om

15

to

22

ft,

thro

ugh

TL

-E

J (1

0%)

at

14.8

ft

, th

roug

h E

J in

4t

h la

min

atio

n (1

00%

) at

20

ft

.

Fai

led

in T

L-E

J (1

5%)

at 2

2.5

ft,

thro

ugh

EJ

in 3

d la

min

atio

n(3

5%)

at

17

ft,

thro

ugh

EJ

in

4th

lam

inat

ion

(85%

) at

19

ft

.

Com

pres

sion

w

rink

ling

in

to

p la

min

atio

n at

19

.7

ft,

fail

ed

in

TL

-E

J (1

00%

) at

24

ft

, th

roug

h E

J in

2d

la

min

atio

n (5

0%)

at

22.5

ft

,th

roug

h 3d

la

min

atio

n.

Fai

led

in T

L t

hrou

gh 3

0% C

K +

GD

at

21.3

ft,

thr

ough

TL

-EJ

(10%

) at

20

.5

ft,

thro

ugh

EJ

in

2d

lam

inat

ion

(10%

) at

16

ft

,th

roug

h E

J in

6t

h la

min

atio

n (4

0%)

at

28.5

ft

.

Fai

led

in T

L-E

J (8

0%)

at 3

0.5

ft,

thro

ugh

EJ

in 2

d la

min

atio

n(7

0%)

at

31

ft,

thro

ugh

EJ

in

3d

lam

inat

ion

(20%

) at

30

.5

ft,

thro

ugh

EJ

in

4th

lam

inat

ion

(20%

) at

25

ft

, th

roug

h E

J in

6t

h la

m-

inat

ion

(10%

) at

20

ft

.

Fai

led

in

TL

-EJ

(25%

) at

24

ft

, th

roug

h E

J in

3d

la

min

atio

n (2

5%)

at 2

6 ft

.

Fai

led

in

2 T

L-E

Js

(25%

at

11

ft

) an

d (1

0%

at

21.2

ft

),

thro

ugh

EJ

in

2d

lam

inat

ion

(15%

) at

17

ft

, th

roug

h E

J in

8t

h la

min

atio

n (2

0%)

at 1

9 ft

.

Com

pres

sion

w

rink

ling

in

to

p la

min

atio

n at

19

.5

ft,

fail

ed

thro

ugh

clea

r T

L

at

23

ft,

thro

ugh

EJ

in

2d

lam

inat

ion

(5%

) at

24

ft

,th

roug

h E

J in

3d

la

min

atio

n (1

00%

) at

25

ft

, th

roug

h E

J in

7th

lam

inat

ion

(10%

) at

22

ft

.

Fai

led

in T

L-E

J (1

5%)

at 2

5.5

ft,

thro

ugh

EJ

in 3

d la

min

atio

n(5

0%)

at

24

ft,

thro

ugh

EJ

in

6th

lam

inat

ion

(50%

) at

30

ft

.

Fai

led

thro

ugh

clea

r T

L

at

15

ft,

thro

ugh

EJ

in

2d

lam

inat

ion

(90%

)at

17

ft

, th

roug

h E

J in

4t

h la

min

atio

n (7

5%)

at

17

ft,

thro

ugh

EJ

in6t

h la

min

atio

n (5

0%)

at

21

ft.

Fai

led

in T

L-E

J (1

0%)

at 2

6 ft

, th

roug

h 6t

h la

min

atio

n.

Fai

led

thro

ugh

clea

r T

L a

t 23

ft

and

foll

owed

1:2

0 S

OG

to

33 f

t,th

roug

h E

J in

6t

h la

min

atio

n (5

0%)

at

25

ft.

Fai

led

in

TL

-EJ

(50%

) at

22

ft

, th

roug

h 4t

h la

min

atio

n.

a MO

R

calc

ulat

ions

in

clud

e de

ad

load

st

ress

.bE

J in

th

e T

Lw

ithi

n th

e >

85%

m

axim

um

mom

ent

regi

on.

Glulam Beam Failure Mapsand Lumber Properties

The following applies to all beam failure maps:

l Lumber properties shown on beam maps are in theform X (Y), where

X = modulus of elasticity (× 106 lb/in2)

Y = specific gravity

l Critical moment (>85 percent maximum moment)region is defined as the area between 7 and 13 ft forthe 8-lamination beams, between 10 and 18 ft forthe 12-lamination beams, and between 12 and 28 ftfor the 17-lamination beams.

l Lowline strength characteristics are also mapped,where

SOG = slope-of-grain

CK = center knot

EK = edge knot

GD = grain deviation

23

28

U. S. GOVERNMENT PRINTING OFFICE: 1993/746-040/60018

Yellow Poplar Glulam Timber Beam Performance

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