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
10 to 2015 to 301:18 to 1:20<1.7E and clear
10 to 2010 to 201:18 to 1:20<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
15
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
a CK, center knot; GD, grain deviation;SOG, slope of grain; EK, edge knot.
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
a CK, center knot; GD, grain deviation;SOG, slope of grain; EK, edge knot.
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
Sample sizeAverage TS
(lb/in2)COV TS (%)TS0.05 (50%)
(1b/in2)TS0.05 (75%)
(lb/in2)Specific gravityMoisture con-
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.
Specimens withEJ failure
Sample sizeAverage TS
(lb/in2)COV TS (%)TS0.05 (50%)
(lb/in2)TS0.05 (75%)
(lb/in2)
No. 2 gradeAll specimens
Sample sizeAverage TS
(lb/in2)COV TS (%)TS0.05 (50%)
(1b/in2)TS0.05 (75%)
(lb/in2)Specific gravityMoisture con-
tent (%)
Specimens withEJ failure
Sample sizeAverage TS
(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
24
25
26
27
28
U. S. GOVERNMENT PRINTING OFFICE: 1993/746-040/60018