performance of red maple glulam timber beamstimber beam designs than does the current standard aitc...

United StatesDepartment ofAgriculture Performance ofForest Service

ForestProducts

Red Maple GlulamLaboratory

ResearchPaperFPL-RP-519

Timber BeamsHarvey B. ManbeckJohn J. JanowlakPaul R. BlankenhornPeter LaboskyRussell C. MoodyRoland Hernandez

Abstract

A red maple glued-laminated (glulam) beam combi-nation that would achieve a design bending stress of2,400 lb/in2 (16.5 MPa) and modulus of elasticity of1.8 × 106 lb/in2 (12.4 GPa) was developed; 45 beamswere evaluated. The properties of the lumber gradesused in the layup and their placement within the beamswere closely monitored during beam fabrication. An-other 166 specimens of end-jointed lumber were gath-ered during manufacture to relate the individual tensilestrength performance of end joints to their performancein the beams. The evaluations of the end-jointed spec-imens and the full-sized beams indicate that a glulambeam combination with the targeted design stress inbending and modulus of elasticity is possible.

Contents

Page

Keywords: Glued-laminated beams, hardwood,modeling, red maple

May 1993

Manbeck, Harvey B.; Janowiak, John J.; Blankenhorn, PaulR.; Labosky, Peter; Moody, Russell C.; Hernandez, Roland.1993. Red maple glulam timber beam performance. Res.Pap. FPL-RP-519. Madison, WI: U.S. Department ofAgriculture, Forest Service, Forest Products Laboratory.30 p.

A limited number of free copies of this publicationare available to the public from the Forest ProductsLaboratory, One Gifford Pinchot Drive, Madison, WI53705-2398. Laboratory publications are sent to more than1,000 libraries in the United States and elsewhere.

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

Introduction . . . . . . . . . . . . . . . . .

Objective and scope . . . . . . . . . . . . . .

Design of beam combinations . . . . . . . . . . .

Procedures for grading lumberand characterizing knots . . . . . . . . . . .

Lumber sawing and grading . . . . . . . . .

Measurement of lumber MOE . . . . . . . .

Characterization of knot properties . . . . . .

Beam and end-jointed lumber tests . . . . . . .

Procedures . . . . . . . . . . . . . . . . .

Beam test results . . . . . . . . . . . . . .

End-jointed lumber tests . . . . . . . . . . .

Analysis . . . . . . . . . . . . . . . . . . .

Effect of beam size . . . . . . . . . . . . .

Design levels . . . . . . . . . . . . . . . .

Comparison with predicted values . . . . . . .

Comparison of beam and end-jointbending strength . . . . . . . . . . . . .

Conclusions . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . .

Appendix A . . . . . . . . . . . . . . . . .

Appendix B . . . . . . . . . . . . . . . . .

Appendix C . . . . . . . . . . . . . . . . .

Appendix D . . . . . . . . . . . . . . . . .

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Red Maple Glulam TimberBeam Performance

Harvey B. Manbeck, Professor, Department of Agricultural Engineering

John J. Janowiak, Assistant Professor of Wood Products

Paul R. Blankenhorn, Professor of Wood Technology

Peter Labosky, Professor of Wood Science and Technology

Pennsylvania State University, University Park, Pennsylvania

Russell C. Moody, Supervisory Research General Engineer

Roland Hernandez, Research General Engineer

Forest Products Laboratory, Madison, Wisconsin

Introduction

Red maple is rapidly becoming a predominant hard-wood species in the forests of the Northeastern UnitedStates. Because this species has not been tradition-ally considered for structural applications, there hasbeen little interest in developing engineered red mapleproducts. The emerging prominence of red maple inthe forests makes product development of vital interestto landowners and to wood processors, fabricators, anddesigners.

Red maple has excellent mechanical properties, treatswell, and has good gluing characteristics (FPL 1987).Thus, it is a good candidate for structural applicationssuch as glued-laminated (glulam) timber beams. TheAmerican Institute of Timber Construction (AITC)established specifications for hardwood glulam timberin AITC 119 (AITC 1985). However, red maple is notincluded as a candidate species for lamination stock.Moreover, this specification provides conservativedesign properties of homogeneous combinations ofhardwood and does not provide options for developingefficient combinations of glulam timber. Consequently,a cooperative research project was conducted betweenthe Pennsylvania State University and the USDAForest Service, Forest Products Laboratory to developefficient combinations of red maple glulam timber. Thetarget design stresses for these combinations were2,400 lb/in2 in bending stress and 1.8 × 106 lb/in2

in modulus of elasticity (MOE). (See Table 1 for SIconversion factors.)

The research reported here was sponsored and fundedby the Pennsylvania Department of Transportation(Project No. SS-043), the Pennsylvania AgricultureExperiment Station, and the U.S. Department

of Agriculture, Forest Service, Forest ProductsLaboratory.

Objective and Scope

The objectives of the research described in this reportwere as follows:

1. to develop a red maple glulam timber beamcombination with a target bending design stresslevel of 2,400 lb/in2 and MOE of 1.8 × 106 lb/in2

2. to establish the technical basis for developingallowable properties for bending strength and MOEof red maple glulam beams

3. to determine if calculation procedures outlined inthe American Society for Testing and Materials(ASTM) D 3737 (ASTM 1991a) can be used topredict bending strength and stiffness of red mapleglulam beams

We expected that successful completion of theobjectives would provide data to support includingred maple in glulam timber design specifications.In addition, the procedures developed could pro-vide the glulam timber industry with better meth-ods for developing more efficient hardwood glulamtimber beam designs than does the current standardAITC 119 (AITC 1985).

The scope of the study included (1) design of beamcombinations, (2) sawing, drying, grading, andcharacterization of properties of a large sample of redmaple structural lumber, (3) manufacture of 45 glulamtimber beams, and (4) evaluation of beam bendingstrength and stiffness.

Results of the laboratory tests of the lumber specimenswill be used to develop input lumber propertiesrequired by advanced probabilistic models (Hernandezand others 1992). Laboratory test results for end-jointed lumber are presented in this report becausethey are critical for the development of a glulamstandard. Results of the glulam beam modeling willbe presented in a separate report.

Design of Beam Combinations

2.0-1/31.8-1/3

No. 2

1.8-1/32.0-1/6

2.0-1/3

1.8-1/3

No. 2

1.8-1/3

2.0-1/6

Glulam beam combinations were designed on the basisof assumed lumber properties of red maple lumber,current surveys of mechanical properties of existingred maple lumber, and procedures established in theASTM D 3737 Standard (ASTM 1991a). The proposedbeam combinations targeted a design bending stress of2,400 lb/in2 and MOE of 1.8 × 106 lb/in2.

The lamination material consisted of E-rated grades oflumber for the outer laminations and visually gradedlumber for the core laminations. The beams contained2.0E material in the outer zones, 1.8E material inthe next inner zones, and No. 2 material in the corelaminations. Edge knots for the lumber grades used forthe two zones on the compression side of the beams andfor the next inner zone on the tension side were limitedto one-third the area of the cross section (two-thirdsclear lumber). This represents No. 2 or better lumberand is designated in the text as 2.0-1/3 lumber for theouter zone and 1.8-1/3 lumber for the next inner zone.The E-rated lumber in the outer tension zone had anedge-knot limitation of one-sixth of the cross section(five-sixths clear lumber) (designated 2.0-1/6 lumber).

Three beam combinations were developed and fab-ricated to represent critical beam sizes with small,medium, and large dimensions (Fig. 1). The smallestbeam (8-Lam) had eight laminations with finished di-mensions of 3 in. wide by 12 in. deep by 20 ft long.The intermediate beam (12-Lam) had 12 laminationswith dimensions of 5 in. wide by 18 in. deep by 30 ftlong. The largest beam (16-Lam) had 16 laminationswith dimensions of 6.75 in. wide by 24 in. deep by40 ft long. The beams were manufactured using nomi-nal 2 by 4, 2 by 6, and 2 by 8 lumber, respectively (1.5by 3.5 in., 1.5 by 5.5 in., and 1.5 by 7.25 in., respec-tively).

The target beam MOE of 1.8 × 106 lb/in2 requiredcertain MOE levels of laminating lumber. To determineif the current resource of red maple structural lumberwould provide adequate yields of the desired E-ratedgrades, preliminary results of ongoing research studiesat both Pennsylvania State University (Janowiak andothers 1992) and the Forest Products Laboratory

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8-Lam3-in. width

12-in. depth20-ft length

12-Lam5-in. width

18-in. depth30-ft length

16-Lam6.75-in. width24-in. depth40-ft length

2.0-1/3

1.8-1/3

No. 2

1.8-113

2.0-1/6

Figure 1—Red maple glulam beam combina-tions. Location of various lumber grades for 8-,12-, and 16-lamination beams.

(FPL) were reviewed. The MOE data indicatedthat the proposed E-rated grades of 2.0-1/6, 2.0-1/3,and 1.8-1/3 could be readily derived from availablered maple lumber populations. Also, results of theknot analysis from the independent sample of redmaple lumber indicated that the lumber quality wasadequate to achieve the targeted 2,400-lb/in2 designbending stress (Green and McDonald, in preparation).Therefore, assumed properties were used to develop theglulam beam combinations (Table 2).

To develop glulam beam combinations that wouldachieve the target bending stress of 2,400 lb/in2,several assumptions were necessary to estimate theminimum strength ratio, the bending stress indices(clear wood stress), and the knot properties required bythe ASTM D 3737 Standard (ASTM 1991a). Values forthe minimum strength ratios of the candidate grades ofred maple were estimated from values established forE-rated lumber across all species in AITC 117 (AITC1979). Bending stress indices for the proposed E-ratedgrades were those recommended by ASTM D 3737.Finally, conservative estimates of knot propertiesrequired by ASTM D 3737 procedures were derivedfor each proposed lumber grade using actual knotmeasurements obtained on an independent sample ofSelect Structural (SS), No. 2, and No. 3 grades of redmaple lumber (Green and McDonald, in preparation).The visually graded lumber was graded accordingto inspection rules established by the NortheasternLumber Manufacturers Association (NELMA 1986).

To achieve the bending stresses predicted with theASTM D 3737 procedures, special grades of lumberwere required in the outer 5 percent of the tensionlaminations (e.g., 5 percent of 16 laminations equaled1 lamination). In this study, one 2.0-1/6 laminationof the red maple combinations was replaced witha lamination meeting the special criteria given inTable 3. These special grades, referred to as tensionlamination grades, were developed following ASTMD 3737. For each beam size, a sample of 15 beamswas selected, which is statistically significant for a10-percent difference in strength properties with a90-percent level of confidence.

Procedures for Grading Lumberand Characterizing Knots

Lumber Sawing and Grading

Lumber for manufacturing glulam beams was obtainedby sawing red maple (Acer rubrum) logs into green8/4 (2-in.) dimensional material. The lumber wasconditioned at a commercial facility, using a predrier,to moisture content of approximately 16 to 18 percentover a 6-week period. Once the target moisture contentlevel was reached, the material was rough-planed toa thickness of 1.75 in. The rough-sawn lumber wasthen visually graded by NELMA rules and subdividedinto Select Structural, No. 1, No. 2, and No. 3 grades(NELMA 1986). The lumber was subsequently shippedto the laminator. Total processed log volume was33.1 × 103 board feet (fbm).

The sawing yielded approximately 4,700, 6,650, and14,100 fbm of 2 by 4, 2 by 6, and 2 by 8 material,respectively. These board footage values were basedon two independent sawmill runs. The first sawmillrun was based on a higher proportion of lower gradelogs, which resulted in poor lumber recovery yieldfor the larger 2 by 8 material. The second run wasmore heavily predisposed to No. 1 and veneer-gradelogs, which enhanced 2 by 8 recovery. Logs in eitherprocessing run were sawn leaving the center log portionin the form of 4 by 4 or larger cants. Yields of thevarious grades were as follows: SS, 32.0 percent;No. 1, 28.7 percent; No. 2, 34.3 percent; No. 3,2.8 percent; and cull, 1.7 percent. These yields werebiased with respect to sawing practices and removal ofcant log sections to minimize the inclusion of juvenilewood.

Measurement of Lumber MOE

Stiffness was measured once the lumber attained anaverage moisture content of 15 percent. The long-span

flatwise bending MOE was measured using a deflectionapparatus with the following specifications:

• steel strongback support assembly equipped withradius supports

• mechanical lever crane for applying a constant148-lb load

• calibrated linear variable differential transformer(LVDT) for measuring midspan displacement

• digital voltmeter for reading output transducervoltage

• portable laptop computer for data entry and storageand MOE computation

The 8- and 10-ft-long lumber was tested over a 7.5-and 9.5-ft span, respectively, using a simply supported,center-point loading configuration. No shear correctionwas made for the apparent MOE calculation as a resultof the large span-to-depth ratio. The results of theMOE tests were used to sort the lumber using thecriteria listed in Table 4.

The SS and No. 1 material was initially sorted to the2.0-1/6, 2.0-1/3, or 1.8-1/3 grades using these criteria.Material that did not meet the criteria was either notused (higher stiffness) or added to the No. 2 grade(lower stiffness). The No. 2 material was then sortedto obtain additional amounts of 2.0-1/3 and 1.8-1/3material. It was expected that much of the No. 2material would not meet these grades and would beused in the beam core. The sorting of the SS and No. 1grades provided nearly all the E-rated material.

Although the lumber samples that were measured forMOE were large, we wanted to determine the aver-age MOE for the lumber specimens that actually ap-peared in the beam layups. We were able to do thisbecause the location of these specimens was specificallymapped. The MOE averages for the lumber that ap-peared in the beam layups are presented in Table 5.These results show that the average stiffness values ofthe 2.0E and 1.8E lumber for each size were slightlylower than the target values. Conversely, the averagestiffness of the No. 2 lumber for each size significantlyexceeded the value of 1.5 × 106 lb/in2 assumed inTable 2.

Characterization of Knot Properties

To accurately analyze the beams for bending strengthusing the ASTM D 3737 (ASTM 1991a) procedures,knots were measured for each grade of lumber afterthe lumber was sorted by MOE. Knots were measuredby estimating an equivalent “straight-through” knotand determining the percentage of the lumber cross-section that the knots occupied. The knot properties

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were measured for all the tension lamination materialand for representative samples of the remaininglumber grades. Knot data were analyzed following theprinciples in USDA Technical Bulletin 1069 (Freas andSelbo 1954).

The knot properties calculated from the knot measure-ments are listed in Table 6. The data were based on aminimum of 1,000 lineal fbm examined for each lamina-tion grade for the three lumber widths combined.

Beam and End-JointedLumber Tests

Forty-five beams (15 of each combination) weremanufactured along with extra specimens for end-jointed lumber tests. The location of each lumberpiece was recorded on prepared beam maps so thatthe lumber properties could later be related to beamperformance. In addition, the quality of the criticaltension laminations was assessed in relation to theallowable knot and slope-of-grain properties, todetermine the relative qualities of the beams.

Procedures

Manufacture of the beams followed the normalproduction procedures (ANSI 1983). Each grade oflumber included a range of qualities permitted bythe grade. Lumber quality was random; the lumberwas not sorted to include high as opposed to lowquality material in any specific arrangement alongthe lamination length. The general manufacturingprocedure was as follows:

1. Lumber pieces were continuously finger-jointed,with the lamination ribbon cut to beam length.Vertically oriented finger-joints were manufacturedwith a melamine–formaldehyde adhesive underradio-frequency cure. Special outer-zone laminationswere manufactured first, followed by production ofcore plies to develop the beam depth profile. End-joint geometry was finger length, 1.03 in.; pitch,0.25 in.; and tip thickness, about 0.03 in. Theobserved tip gap was approximately 0.038 in.

2. Laminations were planed prior to adhesive appli-cation for face bonding. Initial lamination thick-ness was reduced to 1.5 in. by removing 0.13 in. ofmaterial from both faces.

3. The adhesive resin for face lamination was a room-temperature curing resorcinol-formaldehyde.Adhesive application was through a single gluelinewith an 80.lb/1,000-ft2 spread rate. Surfaceadhesive was spread with a roll-coat applicator.Open assembly time was not modified from that

typically used within the operation for SouthernPine beam fabrication. Total closed-assembly timeto applied clamp pressure was approximately50 min. Clamp pressure was similar to that usedfor Southern Pine fabrication.

4. Adhesive cure was at ambient temperature (75°F to80°F) under pressure for a minimum 12-h period.Beams were dressed to a surface finish acceptableunder the category of industrial grade glulam.

Following manufacture, the beams were visuallyinspected to assure conformance to ANSI A190.1(ANSI 1983) and to determine the relative qualitiesof the tension laminations in the midlength regionsubjected to >85 percent of the maximum momentduring test. Using the maximum allowable strength-reducing characteristics listed in Table 3, a relativerating system was developed to systematically assigna quality to the tension lamination. Table 7 lists theallowable percentages of lumber cross-sectional areasthat can be occupied by knots, the slope-of-grainlimitations, and the MOE restrictions for classificationof low, medium, or high quality.

Beam Test Results

Inspection of the beams following manufacture revealedthat two beams (beams RM8-5 and RM8-9) in the16-Lam group had end joints in adjacent laminations inthe outer tension zone spaced closer than the 6 in. re-quired by ANSI A190.1 (ANSI 1983). Also, one beamof each combination had a tension lamination thatdid not meet the visual criteria of Table 3 (beamsRM4-3, RM6-5, and RM8-10). However, the des-ignated compression side of the two smaller beams(RM4-3 and RM6-5) met the criteria, and they weretested with the tension and compression sides reversed(these were balanced combinations). It was not possibleto test the third beam (RM8-10) as a result of both theunbalanced layup of the 16-Lam beam and the qualityof the compression-side lamination. Therefore, althoughthe 15 beams in the 16-Lam group were tested, only12 were included in the final analysis.

The percentage of beams categorized as havinglow, medium, or high quality tension laminations isshown in Table 8. Additional details on the qualityof the individual tension laminations are provided inAppendix A.

All the full-sized glulam beams were tested followingthe procedures given in the ASTM Standard D198(ASTM 1991b). The loading configuration used to testthe full-sized beams is illustrated in Figure 2. Physicalproperties (moisture content, weight, and dimensions),stiffness properties (full-span deflections), and failure

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Figure 2—Loading configurations for bendingtests

load were measured for each beam. In addition, noteswere taken on failures, typical failure types werephotographed, and high-speed videotapes were madeof failures on selected beams. Moisture contents weremeasured with a resistance-type moisture meter nearthe midspan of all laminations after ultimate failure ofthe beams. Weights were measured on a mobile scale tothe nearest 10-lb increment. Dimensions were measuredat each load point.

During the application of load, beam deflections weremeasured using a precision rule (0.02-in. markings)attached to the beam. Deflections were recorded atmid-depth with respect to a stringline attached overeach support. The readings were taken at specifiedload increments with the use of a surveyor’s scope;this allowed the recorder to take readings to thenearest 0.01 in. During the load-deflection readings,elapsed time readings were also taken. The purposefor the elapsed time readings was to record wheninitial cracking occurred (noise) and when compressionwrinkling was first detected. The time-of-occurrencereadings were then traced back to applied load.

After the beams failed, detailed descriptions of thefailure propagations were recorded (Fig. 3), alongwith an assessment of the cause of failure (end joint,

Figure 3—Mapping of failure propagations inglulam beams. (M91 0266-50)

Figure 4—Cumulative distribution of modulus ofrupture (MOR) for three sizes of glulam beams.

knot, etc.). Each beam failure was photographed forfuture reference. Modulus of rupture (MOR) and MOEwere calculated using standard flexural formulas. Deadload stress was included in the MOR calculations. TheMOE values were calculated based on the slope of theload-deflection curve determined by a linear regressionup to design load.

Strength and StiffnessResults of the bending tests on the beams are sum-marized in Table 9. Individual beam results are givenin Appendix B. Figure 4 compares the cumulativedistribution function of MOR for the 8-, 12-, and16-lamination beams.

Beam FailureMost beams failed abruptly at ultimate load and manyemitted cracking sounds as the ultimate load wasapproached. Several beams exhibited compression

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wrinkling at or between the load points prior to max-imum load. All beams ruptured throughout the tensionzone near or within the constant moment region. Al-though it was not possible to positively identify the ini-tial point of failure for all beams, estimates were madeof the mechanism that triggered the initial cause of fail-ure. These results are summarized in Table 10. Beamfailures are described in detail in Appendixes B and C.

Most beams failed through either clear wood orslope-of-grain regions in the tension laminations.The failure of up to two beams in each group wasattributed solely to the finger joints, whereas severalother beams failed by a combination of end jointswith other characteristics. About one-half the beamsexhibited areas of shallow or little wood failure at thebonds between laminations as the rupture progressed.These failures are referred to as glueline failures(GLF) in Appendix B. Although these face bondswere not believed to affect the beam strength, theycould hamper long-term durability. The face bondsare not perceived to be critical in the development ofcommercial red maple glulam lumber. Examination ofthe failed glueline areas suggested that the problemof durability may well be resolved through slightmodification of the lamination assembly, such as slowerplaning speeds and higher face-bonding pressures(private conversation with Bryan River, ResearchForest Products Technologist, FPL).

End-Jointed Lumber Tests

End-jointed lumber specimens from each grade and sizewere tested in tension. The test specimens were 8-ftlong with the end joint located near midspan. Prior totesting, specimens were face- and edge-planed to thesame dimensions of the laminating lumber used in theglulam beams.

For the purpose of characterizing lumber propertiesfor probabilistic models (Hernandez and others 1992),short-span stiffness properties were obtained on the2-ft lumber segment on each side of the joint and onthe 2-ft segment across the joint. These bending testswere conducted on a screw-driven bending machinewith a load cell and LVDT setup for measuring theshear-free deflections between the load points. Theloading configuration for the bending test was 5.5 ftbetween the supports and 2 ft between the appliedload points. Load-deflection readings were taken in5-lb increments. The 2 by 4 specimens were loaded toa maximum load of 300 lb and the 2 by 6 and 2 by 8specimens to a maximum load of 400 lb. The MOEvalues were calculated using the slope of the load-deflection readings.

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Figure 5—Cumulative distribution of tensilestrength of finger-jointed 2.0E-1/6 grade lumberfor nominal 2 by 4, 2 by 6, and 2 by 8 material.

After the nondestructive static bending tests, thespecimens were tested to failure in tension accordingto the procedures specified in the ASTM StandardD 198 (ASTM 1991b), which specify a 5- to 10-mintime-to-failure. Normal quality control practices fortesting end joints would follow the AITC 200 (1991a)procedures, which specify a 2-min time-to-failure. Endjoints for this research project were tested according tothe ASTM D 198 (ASTM 1991b) procedures as a resultof the similar failure times of the full-sized beams. Thetension testing machine was adjusted such that thegrips were 30 in. apart. The specimens were placedin the machine with end joints located near the centerof the 30-in. span. A 30-in. span was used because ofthe minimum span limitations of the tension machine;thus, the 24-in. segment tested in bending was centeredwithin the 30-in. span. After testing, the short-spanstiffness data and the visual grade of the end-jointspecimens between the grips were used to reclassifythe end joints with respect to grade. The strengthand stiffness data provided information to relate therelationship of the individual performance of end jointsto their performance in the beams.

Results of tension tests on the end-jointed tensionlamination material are given in Table 11 and shown inFigure 5. Results on tests of the other grades of fingerjoints are in Appendix D.

Analysis

The glulam beam strength and stiffness results inTable 9 were calculated assuming both the normaland lognormal distributions. However, to analyzethe data, the ASTM D 3737 Standard (ASTM1991a) recommends that a lognormal distribution be

used. Therefore, our analysis assumes a lognormaldistribution.

Effect of Beam Size

By evaluating three beam sizes, it was possible todetermine if beam volume exerted a significant effect onthe strength of red maple beams. The results indicatedthat the small beams (8-Lam) had significantly higherstrength than the other two sizes (Table 9). However,there was no significant difference between the strengthof the other two sizes (12- and 16-Lam). The followingequation is used in the National Design Specificationfor Structural Wood (NFPA 1991) to account for theeffect of varying beam size on bending strength.

(1)

Figure 6—Variation in beam MOR with beamvolume showing a line approximating anexponent of 0.071.

where

b is beam width (in.),

L beam length (ft), and

d beam depth (in.)

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

was conducted. First, the ratio between the volumeeffect factors of each beam size was determined usingboth the 1/10 and 1/20 exponents. Next, the ratio be-tween the averages of the various paired groupings ofbeams were determined along with a confidence inter-val using the procedures described in Appendix II of anFPL report (Wolfe and Moody 1978). Table 12 lists theresults of this analysis.

When width, depth, and length are combined to obtainvolume, the following relationship is used in place of

These results indicate that neither exponent can be

Equation (1) (assuming x = y = z).statistically rejected because predicted results usingboth exponents fell within the confidence interval.

where

(2)

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

For the comparison of the 16- and 12-Lam beams, thepredicted results with the 1/10 exponent were at theedge of the confidence interval whereas those with the1/20 exponent were near the middle of the confidenceinterval.

V volume of actual beam (b by d by L)

k exponent that represents x = y = z

Moody and others (1988, 1990) found that exponents ofx = y = z = 1/10 adequately explained the variationin strength for Douglas-fir beams. A volume effectequation has been adopted by ASTM CommitteeSection D07.02.02 with exponents x = y = z = 1/10for all species. The American Institute of TimberConstruction (AITC), on the other hand, has adoptedthe x = y = z = 1/10 exponents for all species ofglulam except Southern Pine. The parameters adoptedby AITC for Southern Pine are x = y = z = 1/20(AITC 1991b).

Next, a regression analysis was conducted to determinea single exponent to use for x, y, and z that best fitall the data. This exponent was 0.071. The resultingequation is plotted with the bending strength datain Figure 6. Thus, for further analysis, an exponentvalue of 0.071 was used to adjust the beam results to astandard volume.

Design Levels

To determine the most appropriate method of account-ing for variation in beam strength resulting from beamsize. a confidence interval on the ratio of the beam sizes

All beam strengths were adjusted to a standard beamsize of 5.125 in. by 12 in. by 21 ft using the best fitvolume effect relationship (exponent of 0.071). Then,results were pooled and analyzed to determine theappropriate design level using the procedures of ASTMD 2915 (ASTM 1991c). A lognormal distribution wasassumed and the 5th percentile (75 percent tolerance

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Figure 7—Distribution of MOR adjusted tostandard beam size and compared to lognormaldistribution.

limit) was adjusted by dividing by 2.1 to obtain thedesign level. The 2.1 factor includes adjustments forsafety and load duration effects. Figure 7 shows thatthe data closely fit the assumed lognormal distribution.Results shown in Table 13 indicate that the calculatedadjusted 5th percentile (75 percent tolerance limit)significantly exceeded the target level of 2,400 lb/in2.

The average MOE of the three groups of beams wasessentially the same, averaging 1.78 × 106 lb/in2,which rounds off to the target average value of 1.8 ×106 lb/in2. As would be expected with E-rated lumber,the variability of the MOE values was quite low.

Comparison with Predicted Values

StrengthThe same procedure used to design the combinationswas used to reanalyze them with the actual MOE andknot data (Table 5). Because the actual knot sizes weresignificantly smaller than that assumed (Table 2), thecalculated design stress level exceeded the 2,400 lb/in2

value originally predicted.

A comparison of the actual results with those fromthe reanalysis indicated that the actual results stillexceeded the predicted values. The next step in thereanalysis was to permit the bending stress index valueto be increased from the 3,250 lb/in2 value assumedin Table 2. An analysis of the bending stress indexvalues is presented in Figure 8; it shows that a value ofat least 3,500 lb/in2 is justified for the 2.0E1/6 gradelumber used for the outer tension lamination.

Figure B—Analysis of bending stress indexvalues for 2.0E grade red maple lumber basedon results of 42 glulam beam tests.

StiffnessBeam stiffness can be predicted by using the actualstiffness data for the lumber (Table 5) and theprocedures of ASTM D 3737 (ASTM 1991a). Resultsare compared in Table 14 and show that the beamMOE values were within 2 percent of the valuespredicted for the three sizes.

Comparison of Beam and End-JointBending Strength

According to ANSI A190.1, the required end-jointstrength is 1.67 times the nominal design strength inbending. By pooling all of the joint-associated tensilestrength data (lumber size exerted little apparenteffect; Table 10), a 5th percentile (75 percent tolerancelimit using the lognormal distribution) of 5,590 lb/in2

was calculated. This value greatly exceeds the value of4,000 lb/in2 commonly targeted for 24F (2,400 lb/in2)beams. The ratio of the 5th percentile (75 percenttolerance limit) of the combined end-joint data to theadjusted 5th percentile (75 percent tolerance limit) ofthe combined beam data in Table 13 is 1.78, which isslightly higher than the ANSI A190.1 requirements.

Conclusions1. Structural glued-laminated (glulam) timber beams

manufactured with E-rated red maple lumber inthe outer zones and No. 2 lumber in the core metor exceeded the target bending design stress of2,400 lb/in2 and modulus of elasticity (MOE) of1.8 × 106 lb/in2.

8

2. A red maple combination of glulam timber withdesign properties of at least 2,400 lb/in2 in bendingand MOE of 1.8 × 106 lb/in2 is technically feasible.Both the lumber grades and the finger joints usedwould provide adequate strength and stiffness forthis combination.

3. The ASTM D 3737 procedures developed forsoftwood species accurately predict beam stiffnessand provide conservative strength estimates forbeams made with E-rated red maple lumber.

References

AITC. 1979. Determination of design values forstructural glued laminated timber. AITC 117-79. Vancouver, WA: American Institute of TimberConstruction.

AITC. 1985. Standard specifications for hardwoodglued laminated timber. AITC 119-85. Vancouver,WA: American Institute of Timber Construction.

AITC. 1988. Standard specifications for structuralglued-laminated timber of softwood species. AITC117-88—Manufacturing, Vancouver, WA: AmericanInstitute of Timber Construction.

AITC. 1991a. Inspection manual. AITC 200-91. Van-couver, WA: American Institute of Timber Construc-tion.

AITC. 1991b. Use of a volume effect factor in the de-sign of glued laminated timber beams. Tech. Note 21,October. Vancouver, WA: American Institute of Tim-ber Construction.

ANSI. 1983. Structural glued laminated timber. ANSIA190.1. Englewood, CO: American National StandardsInstitute.

ASTM. 1991a. Standard test method for establishingstresses for structural glued-laminated timber (glulam).ASTM D 3737-91. Philadelphia, PA: American Societyfor Testing and Materials.

ASTM. 1991b. Standard methods of static tests of tim-bers in structural sizes. ASTM D198-84. Philadelphia,PA: American Society for Testing and Materials.

ASTM. 1991c. Standard practice for evaluatingallowable properties for grades of structural lumber.

ASTM D2915-90. Philadelphia, PA: American Societyfor Testing and Materials.

Forest Products Laboratory. 1987. Wood handhook–Wood as an engineering material. Agric. Handb.72 (Rev.). Washington, DC: U.S. Department ofAgriculture. 466 p.

Freas, A.D.; Selbo, M.L. 1954. Fabrication anddesign of glued laminated wood structural members.Tech. Bull. 1069. Madison, WI: U.S. Departmentof Agriculture, Forest Service, Forest ProductsLaboratory.

Hernander, R.; Bender, D.A.; Richburg, B.A.; Kline,K.S. 1992. Probabilistic modeling of glued-laminatedtimber beams. Wood and Fiber Science. 24(3):294-306.

Janowiak, J.J.; Manbeck, H.B.; Wolcott, M.P.;Dawlos, J.F. 1992. Final project report on specialproject SS-047-Preliminary refinement of hardwooddesign values. Harrisburg, PA: Pennsylvania Dept. ofTransportation.

Moody, R.C.; Dedolph, C. Jr.; Plantinga, P.L. 1988.Analysis of size effect for glulam beams. Vol. 1.In: Proceedings of the international conference ontimber engineering; 1988 September; Seattle, WA.Madison, WI: Forest Products Research Society:892-898.

Moody, R.C.; Falk, R.; Williamson, T. 1990. Strengthof glulam beams-volume effects. Vol. 1. In: Proceed-ings of the international timber engineering conference;1990 October 23-25; Tokyo. Tokyo: Steering Commit-tee of the International Timber Engineering Confer-ence: 176-182.

NELMA. 1986. Grading rules for northeastern lumber.Cumberland Center, ME: Northeastern LumberManufacturers Association.

NFPA. 1991. National design specification for struc-tural wood. Washington, DC: National Forest ProductsAssociation.

Wolfe, R.W.; Moody; R.C. 1978. Bending strengthof water-soaked glued-laminated beams. Res. Pap.FPL-RP-307. Madison, WI: U.S. Departmentof Agriculture, Forest Service, Forest ProductsLaboratory.

9

Table 1—SI conversion factors

ConversionEnglish unit factor SI unit

board foot (fbm) 0.0024 cubic meter (m3)foot (ft) 0.3048 meter (m)inch (in.) 25.4 millimeter (mm)Fahrenheit (°F) (°F - 32)/1.8 centigrade (°C)pound (lb) 0.4535 kilogram (kg)pound per square

inch (lb/in2) 6.894 Pascal (Pa)

Table 2—Assumed properties of red maplelumber grades for ASTM D 3737 procedures

BendingLamin- MOE stressation (× 106 +ha indexgrade lb/in2) (%) (%) (lb/in

2)b

2.0-1/6 2.0 0.27 12.9 3,2502.0-1/3 2.0 2.63 31.8 3,2501.8-1/3 1.8 2.63 31.8 2,800No. 2 1.5 2.63 31.8 2,500

= average of sum of all knot sizes withineach 1-ft length, taken at 2-in. intervals.

+ h = 99.5 percentile knot size (ASTM 1991a).bClear wood design bending stress.

10

Table 3—Maximum allowable tensionlamination criteriaa

Beam type andlamination criterion

Maximumallowablecharac-teristic

8-Lam

Edge knot + grain deviationCenter knot + grain deviationSlope of grain

12-Lam

40 percent45 percent

1:14

Edge knot + grain deviationCenter knot + grain deviationSlope of grain

16-Lam

30 percent33 percent

1:16

Edge knot + grain deviation 30 percentCenter knot + grain deviation 33 percentSlope of grain 1:16

aASTM 1991a. Knots plus grain deviationsare given in percentage of cross section.

Table 4—Target MOE values and sorting scheme Table 6—Knot properties of laminating lumber

Laminationgrade Sorting and grading criteria

2.0-1/6 Average MOE of 2.0 to 2.1 × 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 of 1/6

(%)

2.0-1/3

1.8-1/3

MOE restrictions same as for 2.0-1/6 gradeEdge knot limitation of 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 of 1/3

Table 5—MOE properties of laminating lumber

Lumber typeand grade

Samplesize

AverageMOE(× 106

lb/in2)COVa

(%)

2 by 4 Lumber

2.0-1/62.0-1/31.8-1/3No. 2

2 by 6 Lumber

2.0-1/62.0-1/31.8-1/3No. 2

2 by 8 Lumber

2.0-1/62.0-1/31.8-1/3No. 2

39 1.96 5.940 1.96 5.880 1.72 8.250 1.80 16.2

52 1.93 7.748 1.92 8.9

215 1.74 10.650 1.73 14.3

141 1.93 9.8144 1.90 8.5193 1.74 10.350 1.69 14.9

Lumber typeand grade

Linealfootage

(ft)+h a

(%)

2 by 4 Lumber

2.0-1/6 386 0.2 14.82.0-1/3 420 0.3 16.81.8-1/3 524 0.6 25.5No. 2 442 0.9 29.2

2 by 6 Lumber

2&1/6 572 0.1 13.62.0-1/3 488 0.4 18.51.8-1/3 376 0.1 7.1No. 2 362 2.0 35.3

2 by 8 Lumber

2.0-1/6 304 0.5 11.22.0-1/3 334 0.7 16.61.8-1/3 436 0.1 7.0No. 2 666 1.7 33.6

= average of sum of all knot sizes withineach 1-ft length, taken at 2-in. intervals.

+ h = 99.5 percentile knot size.

aCOV is coefficient of variation

11

Table 7—Relative rating system for tension lamination quality

Beam type andlamination criterion

D 3737allowable

value

Lamination quality

Lowa Medium High

8-Lam

Edge knot + grain deviationCenter knot + grain deviationSlope of grainMOE (× 106 lb/in2)

40% >30%45% >30%1:14 >1:16

2.0E (avg.) 20% 10%-20%Slope of grain 1:16 >1:18 1:18-1:20MOE (× 106 lb/in2) 2.0E (avg.) 1:20

2.0E (avg.)

Table 9—Results of bending tests on red maple glulam beams

Property 7-Lam 12-Lam 16-Lama 16-Lam

Sample sizeMoisture content (%)

15 1512 12

Normal distribution

Average MOR (lb/in2) 9,070 7,970COV of MOR (%) 13.8 12.4M0R0.05 at 75% tolerance 6,580 6,000Average MOE (× 106 lb/in2) 1.78 1.77COV of MOE (%) 4.3 3.0

Lognormal distribution

Average MOR (lb/in2) 9,080 7,980COV of MOR (%) 14.4 12.1MOR0.05 at 75% tolerance 6,760 6,230

1512

7,890 7,84013.9 14.3

5,720 5,5401.78 1.78

2.5 2.7

7910 7,86015.1 15.8

5,800 5,630

1212

aData in column four exclude the 16-Lam beams thateither did not meet tension lamination requirements(RM8-10) or end-joint spacing requirements (RM8-5, RM8-9).

Table 10—Estimated initial cause ofglulam beam failures

Number of beams

Failure type 8-Lam 12-Lam 16-Lam

Compression followed 4 1 3by tension

Tension in strength- 2 1 3reducing characteristic

Tension in lumber 2 2 2Tension in end joint 7 11 4

13

Table 11—Results of tension tests on end-jointedred maple tension lamination material usinglognormal distributiona

PropertyAll sizes

2 by 4 2 by 6 2 by 8 combined

All specimens

Sample size 20 27 19 66Average TS (lb/in2) 8,310 8,690 8,120 8,410COV TS (%) 28.4 20.7 16.8 22.2

Specimens with failure involving end joint

Sample Size 19 26 18 63Average SGb 0.57 0.57 0.56 0.57Average MC (%) 8.6 8.6 7.8 8.3Average TS (lb/in2) 8,470 8,720 8,010 8,430COV TS (%) 27.6 21.1 16.2 21.9

aTS is tensile strength; SG, specific gravity; and MC,moisture content.

bBased on volume at time of test and ovendry weight.

Table 12—Comparison of beam strength using differentvolume effect exponents

Ratio of predictedmean MOR

Ratio of actualx = y = x = y = mean MOR

Beam comparison z = 0.1 z = 0.05 (average (lower, upper))a

12-Lam and 8-Lam 0.876 0.936 0.879 (0.810, 0.948)16-Lam and 8-Lam 0.803 0.896 0.864 (0.785, 0.943)16-Lam and 12-Lam 0.910 0.954 0.983 (0.909, 1.057)

a90 percent confidence interval

Table 13—Adjusted glulam beambending strength resultsa

Property Result

Sample size 42Average MOR (lb/in2) 8,590COV (%) 13.85th percentile (75% tolerance limit) 6,620Adjusted 5% tolerance limit 3,150

aData adjusted to standard dimensions of5.125 in. width by 12 in. depth by 21 ft length.

Table 14—Comparison of actual and predictedMOE values based on actual lumber properties

Beamtype

Actual Predicted RatioMOE (A) MOE (P) of A/P

8-Lam 1.78 1.78 1.0012-Lam 1.77 1.73 1.0216-Lam 1.78 1.74 1.02

14

Appendix A

Properties of Red Maple Lumber Used forMidlength Region of Outer Tension Lamination

Table Al-Properties of 2 by 4 lumberused in tension lamination

Relativequality of

Tables A1 through A3 list the lumber properties usedfor the tension lamination of 8-Lam, 12-Lam, and 16-Lam beams, respectively. All lumber ranged from 13 to

Beam midlengthno. MOE Characteristica regionb

RM4-1 1.89 Clear16 percent moisture content.

RM4-2

RM4-3c

RM4-4

RM4-5

RM4-6

RM4-7

RM4-8

RM4-9

RM4-10

RM4-11

RM4-12

RM4-13

RM4-14

RM4-15

1.93

2.022.03

1.892.08

1.901.84

1.951.87

2.032.18

1.922.19

1.92

2.021.97

1.99

2.072.20

1.821.93

2.111.89

1.99

1.862.12

1:16 GS

Clear5% GD

1:10 GSClear

40% CK + GDClear

ClearClear

ClearClear

ClearClear

30% EK + GDand 1:16 GS

33% EK + GDClear

Clear

ClearClear

25% EK + GDClear

ClearClear

Blue stain

1:14 GSClear

M

H

L

L

H

H

H

M

L

H

H

M

H

H

M

aCK is center knot, GD grain deviation,and GS slope of grain.

bM is medium, H high, and L low.cTested upside down because ofbelow-grade tension lamination.

15

Table A2—Properties of 2 by 6 lumberused in tension lamination

Relativequality of

Beam midlengthno. MOE Characteristic region

RM6-1 1.97 Clear2.19

RM6-2 1.841.71

RM6-3 1.951.70

RM6-4 1.931.84

RM6-5a 2.041.80

RM6-6 2.011.84

RM6-7 1.642.00

RM6-8 2.111.81

RM6-9 2.031.91

RM6-10 1.982.25

RM6-11 2.022.04

RM6-12 1.881.85

RM6-13 1.65

RM6-14 1.981.97

RM6-15 1.831.90

20% GD

ClearClear

ClearLow MOE

30% EK + GD1:8-1:10 GS

Clear1:16 GS

1:6-1:8 Edge GSClear

Low MOEClear

Clear33% EK + GD

1:12 GS1:16 GS

ClearClear

1:12 GSClear

ClearClear

Worm holesLow MOE

1:18 GSClear

ClearClear

M

H

M

L

M

L

M

L

L

H

L

H

M

M

H

aTested upside down because ofbelow-grade tension lamination.

Table A3—Properties of 2 by 8 lumberused in tension lamination

Beamno. MOE Characteristic

Relativequality ofmidlength

region

RM8-1

RM8-2

RM8-3

RM8-4

RM8-5a

RM8-6

RM8-7

RM8-8

RM8-9a

RM8-10a

RM8-11

RM8-12

RM8-13

RM8-14

RM8-15

2.222.122.14

2.212.13

2.192.21

2.022.001.96

2.062.011.90

2.031.562.10

1.641.88

1.671.97

1.711.55

1.711.62

2.041.811.90

2.082.54

1.401.841.88

1.791.741.98

1.751.96

ClearClearClear

Clear40% GD

35% CK + GDClear

Clear1:6 GS1:8 GS

Clear50% EK + GD

Clear

Clear50% GD + Low MOE

30% EK + GD

Clear + Low MOE1:12 Edge GS

Clear1:8 Edge GS

1:12 GS1:12 GS + Low MOE

ClearClear + Low MOE

Clear1:16 GS + 20% GD

Clear

Clear1:10 GS + 10% CK

+GD

40% CK + GD15% CK + GD30% CK + GD

1:8-1:11 GS1:13 GS10% GD

ClearClear

H

L

L

L

L

L

L

L

L

M

L

M

L

L

H

aBelow-grade tension lamination. Beams weretested in their original orientation as a resultof unbalanced layup.

16

Appendix B

Glulam Beam Results and Failure Descriptions

Tables B1 through B3 list the results of bending testson 8-Lam, 12-Lam, and 16-Lam beams, respectively.

17

Tab

le B

1—R

esu

lts

of b

end

ing

test

s on

8-L

am r

ed m

aple

bea

ms

Bea

mno

.

Dim

ensi

onB

eam

Beam

Tim

e to

Loa

d at

MO

Rb

MO

EFa

ilure

Wid

th

Dep

th

MC

a fa

ilu

refa

ilure

(× 1

03 (

× 1

03ty

pec

(in

.) (

in.)

(%

) (m

in:s

) (×

10

3 l

b)

lb/i

n2)

lb/i

n2)

(EJ

/La

m)

Com

men

td

RM

4-1

3.00

12.0

3 12

2.91

12.0

3 12

2.98

12.0

0 10

3.00

12.0

3 13

2.99

12.5

0 12

3.00

12.0

3 12

3.00

12.0

3 12

2.98

12.0

7 12

2.98

12.0

7 13

5:40

14.6

8

RM

4-2

10:3

017

.72

RM

4-3

6:39

12.0

87.

645

1.73

RM

4-4

9:16

14.5

29.

060

1.62

RM

4-5

10:0

216

.24

RM

4-6

8:36

13.6

2

RM

4-7

12:3

815

.46

RM

4-8

8:03

14.7

2

RM

4-9

6:32

12.1

6

RM

4-10

3.01

12.0

3 14

•

14

:02

17.0

4

9.17

3

11.1

62

10.1

31

8.50

1

9.64

5

9.18

5

7.58

0

10.5

92

1.77

1.87

1.81

1.75 1.75

1.77

1.70

1.86

Lam

Mos

tly

TL fa

ilure

; 5%

EJ

failu

re a

t 10

.5 ft

, pro

paga

ted

thro

ugh

2d L

am;

obse

rved

GLF

from

6.5

to

11 ft

bet

wee

n 2d

and

3d

Lam

s.

Lam

Noi

se a

t 17

× 1

03 lb

; mos

tly

TL f

ailu

re f

rom

11

to 1

2 ft

; 30%

EJ

failu

rein

TL

at 1

2.8

ft, p

ropa

gate

d th

roug

h E

J in

2nd

Lam

at

10.5

ft

(95%

).

Lam

Bea

m t

este

d up

side

-dow

n du

e to

bel

ow-g

rade

TL;

TL

failu

re (

GS)

fro

m6

to 7

ft,

prop

agat

ed t

o G

LF b

etw

een

2d a

nd 3

d La

ms

from

0 t

o 7

ft.

Lam

Noi

se a

t 11

.5 ×

103

lb, m

ostl

y TL

fai

lure

at

9.8

ft; 2

5% E

J fa

ilure

in T

Lat

7.8

ft.

Lam

Noi

se a

t 14

× 1

03 lb

; bri

ttle

TL

failu

re a

t 11

.9 f

t; m

ore

TL f

ailu

re f

rom

5 to

7 f

t, pr

opag

ated

to

EJ

(100

%)

in 2

d La

m a

t 12

.5 f

t.

EJ/

Lam

Noi

se a

t 12

.24

× 10

3 lb

; fai

lure

in T

L fr

om 8

to

13 f

t; al

so 1

0% E

Jfa

ilure

in T

L at

10.

5 ft

; GLF

bet

wee

n 1s

t an

d 2d

Lam

s fr

om 1

3 to

15

ft.

Lam

Noi

se a

t 12

.5 ×

103

lb; c

ompr

essi

on w

rink

ling

in 8

to

12 ft

reg

ion,

init

iate

d at

13.

5 ×

103

lb t

hrou

gh f

ailu

re; a

ll TL

fai

lure

at

7 to

8 f

t

Lam

Noi

se a

t 14

.2 ×

103

lb; T

L fa

ilure

(G

S) f

rom

9 t

o 12

ft;

seve

ral G

LFs

ingl

uelin

es b

etw

een

4th

and

5th

Lam

s.

Lam

Noi

se a

t 10

.2 ×

103

lb; 1

0% E

J fa

ilure

in T

L at

10.

6 ft

, pro

paga

ted

thro

ugh

EJ

in 3

d La

m a

t 11

.8 ft

.

Lam

TL f

ailu

re f

rom

12.

5 to

13.

8 ft

, pro

paga

ted

to E

J (5

%)

in 2

d La

m a

t9.

6 ft

; com

pres

sion

wri

nklin

g in

8 t

o 12

ft r

egio

n, in

itia

ted

at 1

5,20

0 ×

103

lb.

(Pag

e 1

of 2

)

Ta

ble

B1—

Res

ult

s o

f b

end

ing

tes

ts o

n 8

-La

m r

ed m

ap

le b

eam

s-co

n.

Bea

mno

.

Dim

ensi

onB

eam

Bea

mTi

me

toLo

ad a

tM

OR

bM

OE

Failu

reW

idth

Dep

th M

Ca

failu

refa

ilu

re

(×

103

(×

103

type

c

(in

.)

(in

.)

(%)

(min

:s)

(×

103

lb)

lb/in

2 )

lb/in

2 )

(EJ/

Lam

)C

omm

entd

RM4-

113.

0012

.07

128:

2315

.18

9.41

01.

88EJ

No

nois

eun

til f

ailu

re; 1

00%

EJ

failu

re in

TL

at 1

2.5

ft; G

LF b

etw

een

4th

and

5th

Lam

s.RM

4-12

2.95

12.0

512

11:0

416

.12

10.1

921.

75EJ

No

nois

eun

til f

ailu

re;

100%

EJ

failu

re i

n TL

at

10.3

ft;

britt

le f

ailu

reth

roug

h 2d

and

3d

Lam

s; G

LF b

etw

een

5th

& 6

th a

nd 6

th &

7th

Lam

s.RM

4-13

2.97

12.0

513

5:15

10.6

86.

717

1.77

Lam

No

nois

eun

til f

ailu

re; b

ritt

le T

L fa

ilure

at

11.3

ft; G

LF b

etw

een

2d &

3d a

nd 5

th &

6th

Lam

s.

RM4-

142.

9712

.03

128:

1314

.98

9.44

11.

92La

mN

oise

at

10.7

× 1

03 lb

; com

pres

sion

wri

nklin

g, in

itia

ted

at 1

3.6

× 10

3 lb

at 1

2 ft

; bri

ttle

TL

failu

re a

t 10

.5 ft

; GLF

bet

wee

n 2d

and

3d

Lam

s fr

om13

to

17ft.

RM4-

153.

0012

.05

136:

4512

.23

7.61

11.

81La

mN

oise

at

6.5

× 10

3 lb

; TL

failu

re a

t 7

to 1

0 ft

to

EJ

(25%

) in

2d

Lam

at

11.3

ft;

slig

ht c

ompr

essi

on w

rink

ling

at f

ailu

re a

t 12

.5 f

t.

a MC

is

moi

stur

e co

nten

t.b M

OR

cal

cula

tions

inc

lude

d de

ad l

oad

stre

ss.

c EJ

is e

nd jo

int,

GLF

glu

elin

e fa

ilure

, GS

slop

e of

gra

in, a

nd T

L te

nsio

n la

min

atio

n.

(Pag

e 2

of 2

)

Tab

le B

2—R

esu

lts

of b

end

ing

test

s on

12-

Lam

red

map

le b

eam

s

Bea

mno

.

Dim

ensi

onB

eam

Beam

Tim

e to

Load

at

MO

Ra

MO

EFa

ilure

Wid

th

Dep

th

MC

fa

ilu

refa

ilure

(× 1

03 (

× 1

03ty

pe(i

n.)

(i

n.)

(%

) (m

in:s

) (×

1

03

lb)

lb/i

n2)

lb/i

n2)

(EJ

/La

m)

Com

men

tb

RM

6-1

5:40

28.3

67.

161.

85La

m

RM

6-2

7:23

33.7

58.

503

1.78

EJ

RM

6-3

9:38

40.9

910

.240

1.73

EJ

RM

6-4

5:31

27.8

96.

982

1.76

EJ/

Lam

RM

6-5

5.00

18.0

9 12

5.00

18.0

6 12

5.00

18.0

9 11

5.00

18.1

0 11

5.00

18.1

0 12

6:23

31.2

07.

808

1.73

EJ/

Lam

RM

6-6

5.00

18.0

5 12

8:15

35.6

08.

945

1.78

EJ/

Lam

RM

6-7

5.00

18.0

5 13

5.00

18.0

5 13

5.00

18.0

6 12

4.95

18.0

6 11

8:24

36.5

19.

172

1.78

Lam

RM

6-8

7:08

32.0

08.

050

1.78

Lam

RM

6-9

5:20

27.6

56.

961

1.83

EJ/

Lam

RM

6-10

5:47

28.5

97.

267

1.78

EJ/

Lam

Noi

se a

t 15

× 1

03 lb

; TL

failu

re a

t 12

to

17 f

t; 5%

EJ

failu

re in

TL

at11

.6 ft

.

Noi

se a

t 15

× 1

03 lb

; 60%

EJ

failu

re in

TL

at 1

2.5

ft; G

LF b

etw

een

7th

and

8th

Lam

s fr

om 6

to

8 ft

.

Noi

se a

t 23

× 1

03 lb

; 100

% E

J fa

ilure

in T

L at

15

ft; c

ompr

essi

onw

rink

ling

at f

ailu

re a

t 15

.3 a

nd 1

7.2

ft.

Noi

se S

t 13

× 1

03 lb

; 50%

EJ

failu

re in

TL

at 1

6.3

ft, p

ropa

gate

d to

100%

EJ

failu

re in

3d

Lam

at

17.3

ft.

Bea

m t

este

d up

side

-dow

n du

e to

bel

ow-g

rade

TL;

noi

se a

t 25

.5 ×

103

lb; 4

0% E

J fa

ilure

in T

L at

17.

5 ft

; sev

eral

GLF

s be

twee

n 6t

h an

d 7t

hLa

ms.

Noi

se a

t 14

.2 ×

103

lb; 7

0% E

J fa

ilure

in T

L at

20.

6 ft

, als

o TL

fai

lure

at 1

7.5

ft; G

LF b

etw

een

5th

and

6th

Lam

s; s

econ

dary

EJ

failu

re (7

5%)

in 2

nd L

am a

t 16

.6 ft

.

Noi

se a

t 26

× 1

03 lb

; all

TL f

ailu

re f

rom

13

to 1

4 ft

; GLF

bet

wee

n 4t

han

d 5t

h La

ms

from

0 t

o 9

ft.

Noi

se a

t 18

.5 ×

103

lb;

TL

failu

re (

GD

) fr

om 1

4 to

16

ft; G

LF b

etw

een

6th

and

7th

Lam

s fr

om 2

2 to

25

ft.

Noi

se a

t 21

.5 ×

103

lb; 3

0% E

J fa

ilure

in T

L at

14.

5 ft

, pro

paga

ted

thro

ugh

EJ

(50%

) in

2d

Lam

at

16 f

t.

Noi

se a

t 21

× 1

03 lb

; 40%

EJ

failu

re in

TL

at 1

1.8

ft, a

lso

TL f

ailu

refr

om 1

1.8

to 1

4.5

ft, t

hen

to E

J (5

0%)

in 2

d La

m a

t 14

.3 f

t; G

LFbe

twee

n 4t

h an

d 5t

h La

ms.

(Pag

e 1

of 2

)

Ta

ble

B2—

Res

ult

s o

f b

end

ing

tes

ts o

n 1

2-L

am

red

ma

ple

bea

ms-

con

.

Dim

ensi

onB

eam

Bea

mTi

me

toLo

ad a

tM

OR

aM

OE

Failu

reBe

amW

idth

Dep

th M

Cfa

ilure

fail

ure

(×

10

3 (×

10

3ty

peno

.(i

n.)

(i

n.)

(%

) (m

in:s

) (×

1

03

lb)

lb/i

n2)

lb/i

n2)

(EJ

/La

m)

Com

men

tb

RM6-

115.

0018

.10

105:

0726

.64

6.68

11.

82La

mN

oise

at

25 ×

103

lb; m

ostl

y TL

fai

lure

at

16.5

ft;

5% E

J fa

ilure

at

17 f

t;G

LF b

etw

een

1st

and

2d L

ams

from

11

to 1

6 ft

.

RM6-

125.

0018

.10

118:

3834

.90

8.72

31.

67E

J/La

mN

oise

at

16.5

× 1

03 lb

; 25%

EJ

failu

re a

t 17

.6 f

t, to

100

% E

J fa

ilure

in2d

Lam

at

18.3

ft; G

LF b

etw

een

4th

and

5th

Lam

s fr

om 2

1 to

24

ft.

RM6-

134.

9518

.05

126:

2230

.90

7.85

51.

79La

mN

oise

at

23.5

× 1

03 lb

; all

TL f

ailu

re a

t 14

.3 f

t, to

100

% E

J fa

ilure

in 2

dLa

m a

t 14

.5 ft

; GLF

bet

wee

n 2d

and

3d

Lam

s fr

om 1

2 to

14

ft.

RM

6-14

5.00

18.0

5 13

5:47

29.0

07.

304

1.76

EJN

oise

at

17 ×

103

lb; 7

5% E

J fa

ilure

in T

L at

11.

3 ft

, pro

paga

ted

to30

% E

J fa

ilure

in 4

th L

am a

t 17

.7 ft

.

RM6-

155.

0018

.08

127:

1531

.71

7.95

21.

67E

J/La

mN

oise

at

9.5

× 10

3 lb

; 100

% E

J fa

ilure

in T

L at

11.

7 ft

; TL

failu

re f

rom

9 to

11.

7 ft

; GLF

bet

wee

n 1s

t an

d 2d

Lam

s.

a MO

R c

alcu

latio

ns i

nclu

ded

dead

loa

d st

ress

.b E

J is

end

join

t, G

D g

rain

dir

ecti

on, G

LF g

luel

ine

failu

re, G

S sl

ope

of g

rain

, and

TL

tens

ion

lam

inat

ion.

(Pag

e 2

of 2

)

Tab

le B

3—R

esu

lts

of b

end

ing

test

s on

16-

Lam

red

map

le b

eam

s

Bea

mno

.

Dim

ensi

onB

eam

Bea

mTi

me

toLo

ad a

tM

OR

aM

OE

Failu

reW

idth

Dep

th M

Cfa

ilure

failu

re(×

103

(×

103

type

(in

.)

(in

.)

(%)

(min

:s)

(×

10

3

lb)

lb/i

n2)

lb/i

n2)

(EJ

/La

m)

Com

men

tb

RM

8-1

RM

8-2

8:52

69.6

09.

690

1.82

Lam

6:25

57.0

07.

980

1.82

Lam

RM

8-3

6:52

60.0

08.

399

1.79

EJ

RM

8-4

RM

8-5

5:15

47.5

06.

697

1.77

EJ/

Lam

8:36

48.5

06.

907

1.75

Lam

RM

8-6

12:3

854

.30

7.68

11.

77La

m

RM

8-7

6.75

24.1

2 14

6.75

24.0

9 11

6.74

24.0

9 11

6.70

24.1

3 11

6.70

24.0

0 12

6.75

23.9

7 12

6.75

24.0

0 13

6.75

23.9

4 13

6.75

23.9

4 12

8:03

59.2

08.

342

1.78

EJ/

Lam

RM

8-8

6:32

50.6

07.

184

1.81

RMB-

914

:02

58.0

08.

217

RM

8-10

6.75

24.2

0 11

8:07

66.5

09.

202

1.77

1.79

Lam

Lam

Noi

se a

t 43

× 1

03 lb

; TL

failu

re f

rom

16

to 2

0 ft

.

Noi

se a

t 41

× 1

03 lb

; TL

failu

re (

GD

) at

24.

5 ft

, pro

paga

ted

to 5

0% E

Jfa

ilure

in

2d L

am a

t 24

ft.

Noi

se a

t 43

× 1

03 lb

; 100

% E

J fa

ilure

in T

L at

18.

3 ft

; com

pres

sion

wri

nklin

g at

fai

lure

at

22 f

t.

Noi

se a

t 13

× 1

03 lb

; 50%

EJ

failu

re in

TL

at 2

5 ft

.

Noi

se a

t 20

.5 ×

103

lb; s

tack

ed E

J in

Lam

s 2

and

3 (1

8.7

ft a

nd18

.6 f

t)c ;

join

ts n

ot a

ssoc

iate

d in

fai

lure

–all

TL f

ailu

re f

rom

24

to 2

5 ft

.

Noi

se a

t 18

× 1

03 l

b; T

L fa

ilure

(G

D)

at 1

6.5

ft, p

ropa

gate

d to

50%

EJ

failu

re in

2d

Lam

at

17 ft

.

Noi

se a

t 20

× 1

03 lb

; 75%

EJ

failu

re in

TL

at 1

8 ft

; 1:1

2 ed

ge G

S in

TL

at 1

7.5

ft le

adin

g in

to 7

5% E

J fa

ilure

in 2

d La

m a

t 17

ft.

Noi

se a

t 38

× 1

03 l

b; T

L fa

ilure

(G

S) f

rom

20

to 2

1 ft

, pro

paga

ted

to80

% E

J fa

ilure

in 2

nd L

am a

t 20

.5 ft

.

Noi

se a

t 33

× 1

03 lb

; 10%

EJ

failu

re in

TL

at 2

0 ft

, pro

paga

ted

thro

ugh

EJ

(100

%) i

n 2d

Lam

at

22.5

ft; c

ompr

essi

on w

rink

ling

at fa

ilure

in t

opLa

m a

t 19

ft;

EJ

stac

ked

in 1

st a

nd 2

nd L

ams

at 1

2 ft

–not

invo

lved

infa

ilure

.c

Noi

se a

t 34

× 1

03 lb

; all

TL f

ailu

re a

t 15

ft,

prop

agat

ed t

o 15

% E

Jfa

ilure

in 2

d La

m a

t 14

ft; G

LF b

etw

een

4th

and

5th

Lam

s; T

L di

d no

tm

eet

crite

ria.

(Pag

e 1

of 2

)

Tab

le B

3—R

esu

lts

of b

end

ing

test

s on

16-

Lam

red

map

le b

eam

s—co

n.

Dim

ensi

onB

eam

Bea

mTi

me

toLo

ad a

tM

OR

a M

OE

Failu

reB

eam

Wid

th D

epth

MC

failu

refa

ilu

re

(×

103

(×

103

type

no.

(in

.)

(in

,)

(%)

(min

:s)

(×

10

3

lb)

lb/i

n2)

lb/i

n2)

(EJ

/La

m)

Com

men

tb

RM8-

116.

7524

.03

106:

2854

.10

7.61

51.

87E

J/La

mN

oise

at

22 ×

103

lb; 8

0% E

J fa

ilure

in T

L at

15.

5 ft

, pro

paga

ted

to15

% E

J fa

ilure

in 2

d La

m a

t 19

.5 ft

; GLF

bet

wee

n 3d

and

4th

Lam

sfr

om 1

to

7 ft

.

RM

8-12

6.75

24.0

8 11

5:15

59.5

08.

328

1.75

EJN

oise

at

38 ×

103

lb; 1

00%

EJ

failu

re in

TL

at 2

2.5

ft; c

ompr

essi

onw

rink

ling

first

det

ecte

d in

top

Lam

at

53 ×

103

lb.

RM

8-13

6.75

24.0

0 12

8:13

36.6

05.

203

1.68

EJ/

Lam

Noi

se a

t 28

× 1

03 lb

; 50%

EJ

failu

re in

TL

at 1

4 ft

; GLF

bet

wee

n 7t

han

d 8t

h La

ms

from

24

to 3

0 ft

.

RM8-

14

6

.75

24.0

0 13

7:40

59.0

08.

313

1.75

EJN

oise

at

34.5

× 1

03 lb

; 95%

EJ

failu

re in

TL

at 1

5.5

ft, p

ropa

gate

d to

25%

EJ

failu

re i

n 2d

Lam

at

17 f

t; co

mpr

essi

on w

rink

ling

first

det

ecte

din

top

Lam

at

55 ×

103

lb; G

LF b

etw

een

9th

and

10th

Lam

s fr

om 2

4 to

33 f

t.

RMB-

156.

7524

.00

127:

3361

.50

8.66

21.

76La

mN

oise

at

16 ×

103

lb; a

ll TL

fai

lure

at

18 f

t; G

LF b

etw

een

7th

and

8th

Lam

s at

12

ft.a M

OR

cal

cula

tions

inc

lude

dea

d lo

ad s

tres

s.b E

J is

end

join

t, G

D g

rain

dir

ecti

on, G

LF g

luel

ine

failu

re, G

S sl

ope

of g

rain

, and

TL

tens

ion

lam

inat

ion.

c Did

not

mee

t A

NSI

A19

0.1

requ

irem

ents

.

(Pag

e 2

of 2

)

Appendix C

Glulam Beam Failure Maps and Lumber Properties

Location of failures in the tension zone of the beamsis given in the figures. Failure through end joints isreported by an indication of the percentage of thefailure that occurred at the joint itself. Modulus ofelasticity values are given for each piece of lumber inthe outer tension zone; the locations with reference toone end are given at the bottom of each figure.

24

Beam No. RM4-1 Beam No. RM4-2

Beam No. RM4-3

Beam No. RM4-5



B e a m No. R M 4 - 4

Beam No. RM4-6

25




26






27


Beam No. RM6-15




28



Beam No. RMB-11 Beam No. RM8-12


Beam No. RM8-15

29

Appendix D

Properties of Red Maple End-Jointed Lumber for

Grades Other Than Tension Lamination Quality

Table D—Results of tension tests on red mapleend-jointed lumber for grades other thantension lamination quality using thelognormal distribution

AllStatistics reported include results for all end-jointspecimens considered and for those specimens withjoint-associated failures.

Lumber size sizescom-

Grade and property’ 2 by 4 2 by 6 2 by 8 bined

2.0-1/6

All specimens

Sample size 10 20 5 35Average TS (lb/in2) 6,950 7,130 6,880 7,020TS COV (%) 26.6 20.7 59.3 28.9

End-joint failures

Sample size 8 16 5 29Average SG 0.57 0.57 0.57 0.57Average MC (%) 8.7 8.9 7.1 8.5Average TS (lb/in2) 7,030 7,160 6,880 7,050TS COV (%) 30.0 21.1 59.3 31.0

1/3 EKc

All specimens

Sample size 14 19 21 54Average TS (lb/in2) 7,060 6,450 6,520 6,630TS COV(%) 23.3 29.3 25.2 26.1

End-joint failures

Sample size 9 12 13 34Average SG 0.54 0.52 0.55 0.54Average MC (%) 8.7 8.5 7.4 8.1Average TS (lb/in2) 7,040 6,580 6,830 6,790TS COV (%) 15.2 31.9 20.1 23.6

No. 2

All specimens

Sample size 4 4 3 11Average TS (lb/in2) 5,720 5,180 4,990 5,270TS COV (%) 35.1 43.7 3.9 30.9

End-joint failures

Sample size 1 3 1 5Average SG. 0.64 0.52 0.59 0.56Average MC (%) 8.7 8.8 8.4 8.7Average TS (lb/in2) 6,230 5,740 5,160 5,670TS COV (%) 50.6 — 35.9

aTS is tensile strength, SG specific gravity, andMC moisture content.

bSpecimens with failures involving an end joint.cBecause of the percentage of small sample sizes, resultsfor 2.0-1/3 and 1.8-1/3 grades were combined.

30

performance of red maple glulam timber beamstimber beam designs than does the current standard aitc...

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