1、Designation: D 3737 07Standard Practice forEstablishing Allowable Properties for Structural GluedLaminated Timber (Glulam)1This standard is issued under the fixed designation D 3737; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the procedures for establishingallowable properties for structural glued laminated t
3、imber.Included are the allowable stresses for bending, tension andcompression parallel to the grain, horizontal shear, compres-sion perpendicular to the grain, and radial tension and com-pression in curved members. Also included are modulus ofelasticity and modulus of rigidity.1.2 This practice is l
4、imited to the calculation of allowableproperties subject to the given procedures for the selection andarrangement of grades of lumber of the species considered.1.3 Requirements for production, inspection and certifica-tion are not included, but in order to justify the allowableproperties developed u
5、sing procedures in this practice, manu-facturers must conform to recognized manufacturing standards.Refer to ANSI/AITC A190.1 and CSA 0122.1.4 The values stated in inch-pound units are to be regardedas standard.1.5 This standard does not purport to address all of thesafety concerns, if any, associat
6、ed with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D9 Terminology Relating to Wood and Wood-Based Prod-uctsD 198
7、 Test Methods of Static Tests of Lumber in StructuralSizesD 245 Practice for Establishing Structural Grades and Re-lated Allowable Properties for Visually Graded LumberD 2395 Test Methods for Specific Gravity of Wood andWood-Based MaterialsD 2555 Practice for Establishing Clear Wood Strength Val-ues
8、D 2915 Practice for Evaluating Allowable Properties forGrades of Structural LumberD 4761 Test Methods for Mechanical Properties of Lumberand Wood-Base Structural MaterialD 5456 Specification for Evaluation of Structural Compos-ite Lumber ProductsD 6570 Practice for Assigning Allowable Properties for
9、Mechanically Graded LumberE 105 Practice for Probability Sampling Of Materials2.2 Other Standards:ANSI/AITC A190.1 Structural Glued Laminated Timber3ANSI/AF physical properties such as specific gravity; andmechanical properties such as modulus of elasticity shall bebased on measurements of 236 lumbe
10、r for definition of gradecharacteristics.4.1.7.2 The effect of decay or compression failures uponstrength cannot be readily determined, thus these defects shallbe prohibited from laminating grades insofar as existinginspection and grading technology permit. Firm white speck orlight white pocket is p
11、ermissible in grades of lumber thatpermit knots to occupy up to one third or more of the crosssection provided their extent in combination with knots doesnot exceed that of the largest edge knot permitted. Theexception is that firm white speck and light white pocket shallbe excluded from end joints
12、in tension members and the outer10 % of the total depth on the tension side of bendingmembers.4.1.7.3 Compression wood (as defined in Terminology D9)in readily identifiable and damaging form shall be limited inaccordance with 4.1.7.3(1) and 4.1.7.3(2).(1) For dry service conditions, grades permittin
13、g knots upto one half of the cross section may contain streaks ofcompression wood occupying as much as 20 % of the crosssection. Streaks of compression wood up to one eighth of thecross section may be permitted in other grades.(2) For wet service conditions, or for pressure-treatedmembers, the condi
14、tions of 4.1.7.3(1) apply except that com-pression wood is limited to 5 % of the cross section of thelaminations in tension members and in the outer 10 % of thetotal depth on the tension side of bending members.4.1.7.4 Lumber shall be free of shakes and splits that makean angle of less than 45 with
15、the wide face of the piece. Pitchpockets shall be limited in size to the area of the largest knotpermitted, and pitch streaks shall be limited to one sixth of thewidth of the lumber.4.1.7.5 The range of moisture content of lumber for assem-bly into a single member shall not exceed five percentagepoi
16、nts, except when all the lumber is 12 % or lower. Themaximum moisture content of individual laminations is 16 %,unless the in-service conditions are wet service and in this casethe maximum is 20 %.TABLE 1 Adjustment Factors for Clear Wood Stresses(Test Methods D 2555)PropertyMultipliers for Average
17、or5th PercentileSeasoning Fac-tor for a 12 %Average Mois-ture ContentSoftwoods HardwoodsBending 0.476 0.435 1.35Compression parallel to grain 0.526 0.476 1.75Modulus of elasticity 1.095 1.095 1.20Horizontal shear 0.244 0.222 1.13D37370724.2 Requirements for Adhesives4.2.1 Adhesives for use in struct
18、ural glued laminated timbershall be rigid (non-elastomeric) to ensure composite action ofthe laminations and shall be sufficiently strong to transferstresses required by the intended use of the member.4.2.2 Adhesives shall be sufficiently durable to providebond for the life of the glued laminated me
19、mber in its expectedservice environment.4.3 Tension Laminationsfor horizontally laminated bend-ing members shall meet the requirements herein.4.3.1 The results of full-size beam tests reported in Refs (6,10, and 11)6have yielded an empirical relationship between thesize of knots in the tension zone
20、and bending strength. Thisrelationship dictates that special grading considerations beapplied to the laminations used in the outer 10 % of the beamdepth on the tension side.This tension side may exist on the topor bottom of the beam, or both, depending upon loading andsupport conditions. If horizont
21、ally laminated timbers are manu-factured without applying these special tension laminationgrading considerations, the allowable bending stress shall bereduced by multiplying the allowable stress calculated in7.2.1.1 by 0.85 if the depth is 15 in. (0.38 m) or less or by 0.75if the depth exceeds 15 in
22、. (0.38 m).4.3.2 Visually Graded Lumber:4.3.2.1 Definitions of terms required for calculation of knotand grain deviation restrictions are listed in 3.1.9-3.1.13.4.3.2.2 Knots and local grain deviations are expressed as aratio of the cross-sectional area they occupy to the cross-sectional area of the
23、 lumber based on the dressed width of thelumber. They are measured using the displacement technique.Knots are measured to the lateral extremes of the knot; graindeviations (with or without knots) are measured to the lateral6The boldface numbers in parentheses refer to a list of references at the end
24、 ofthis practice.TABLE 2 Bending Stress Index Based on Large Beam Tests and Modulus of Elasticity Values for Visually Graded LumberNOTE 1Appendix X1 provides one method of developing new data.Species Growth ClassificationABending Stress IndexBModulus of Elasticitypsi MPa million psi MPaDouglas Fir-L
25、arch medium grain 3000 20.7 1.9 13 100close grain 3250 22.4 2.0 13 800dense 3500 24.1 2.1 14 500Southern Pine coarse grainC2000 13.8 1.5 10 300medium grain 3000 20.7 1.8 12 400dense 3500 24.1 2.0 13 800Hem-Fir medium grain 2560 17.7 1.7 11 700denseD3000 20.7 1.8 12 400AClassification for “dense” woo
26、d shall follow Practice D 245.BValues shown are based on full-size beam tests. As a result, these values incorporate the effects of some features such as grain deviations in lumber along withinfluences of end and face bonding influences. Beams designed using these values and tested in accordance wit
27、h Test Methods D 198 will yield strength values such thatthe lower fifth percentile will exceed the design bending stress by a factor of 2.1 with 75 % confidence. Analysis of test data assumed a log normal distribution. Forunsymmetric combinations, tests have shown that values up to 40 % higher than
28、 those listed may be applied to the compression side of bending members.CAlso applicable to minor species of southern pine regardless of growth rate.DSpecific gravity, based on oven-dry weight and volume at 12 % moisture content, must equal or exceed 0.39.TABLE 3 Bending Stress Indexes and Compressi
29、on Stress IndexParallel to Grain for E-Rated Lumber Used in LaminatingALong Span,E, psiBending StressIndexACompression StressIndex Parallelto GrainB,Cpsi MPa psi MPa1 600 000 2560 17.7 1900 13.11 900 000 3000 20.7 2400 16.52 100 000 3500 24.1 2800 19.32 300 000 4000 27.6 3100 21.4AValues shall be no
30、t higher than obtained by interpolation for intermediate Evalues.BValues are for 12-in. deep members at 12 % moisture content (dry).CValues are for members at 12 % moisture content (dry) values.TABLE 4 Parallel to Grain Stress Modification FactorsAssociated with Slope of Grain for DesigningGlulam Co
31、mbinationsSlope of GrainStress Modification FactorTension Compression1:4 0.27 0.461:6 0.40 0.561:8 0.53 0.661:10 0.61 0.741:12 0.69 0.821:14 0.74 0.871:15 0.76 1.001:16 0.80 1.001:18 0.85 1.001:20 1.00 1.00TABLE 5 Constant Used to Adjust Vertically Laminated BendingStrength RatioStrength Ratio (SR1)
32、 C10.45 or greater 1.2380.40 1.2920.35 1.3460.30 1.4000.26 or less 1.444TABLE 6 Grade Adjustment Factors for Modulus of ElasticityBending Strength RatioAAdjustment Factor0.55 or greater 1.000.45 to 0.54 0.900.44 or less 0.80ADetermined in accordance with Practice D 245.D3737073extremes of the zone w
33、ithin which the local slope of grainexceeds the allowable slope of grain for the grade. Eq 8-11which follow yield the maximum allowable knot and graindeviation ratios in the outer 10 % of depth. It is suggested theseratios be adjusted downward to the nearest 0.05 or to the nextnearest convenient fra
34、ction (such as13).4.3.2.3 Beams Greater than 15 in. (0.38 m) in Depth:(1) Outer 5 %Grain deviation shall be limited in accor-dance with Eq 1 and 2.GDS#1.551SRtl! (1)GDS#1.821SRtl! (2)(a) Eq 1 shall be used when GDE, with or without GDC,is used to determine GDS (Fig. 1). Eq 2 shall apply when GDEis n
35、ot used to determine GDS. In addition, general slope ofgrain shall not exceed 1:16 if the required strength ratio of thetension lamination is 0.60 or greater. If SRtlis less than 0.60,the general slope of grain shall not exceed 1:12.(2) Next Inner 5 %Knots are restricted in accordancewith Eq 3 and 4
36、.KE 5 0.66 0.45 SRtl(3)KC 5 1.20 0.93 SRtl(4)(a) General slope of grain shall be limited in accordancewith the strength requirements of the individual laminations.4.3.2.4 Beams 12 in. (0.30 m) to 15 in.(0.38 m) in Depth:(1) Outer 5 %The requirements of 4.3.2.3(1) applyexcept that SRtlshall be multip
37、lied by 0.90 in Eq 1 and 2. Thevalue of 0.9 SRtlshall not be taken as less than 0.50.(2) Next Inner 5 %General slope of grain shall be limitedin accordance with the strength requirements of the individuallaminations.(a) (b)GDC = y/b GDC = y/bGDE = z/b GDE = z/bGDS = x/b where x=y+z GDS= x/b where xy
38、+z(a) Example of grain deviations not associated with a knot where the projectedgrain deviations do not overlap.(b) Example of grain deviations associated with knots where the projected graindeviations overlap.FIG. 1 Knot and Grain Deviation Measurement at the Outer 5 % on the Tension Side of a Memb
39、er Occurring in a 1-ft LengthNOTE 1When edge knots and centerline knots occur at the same cross section, the sum of the edge knots and centerline knots is used in calculatingKC as shown in (b).FIG. 2 Knot Measurement for the Next Inner 5 % on the Tension Side of a Bending MemberD37370744.3.2.5 Beams
40、 of Four or More Laminations and Less than12 in. (0.30 m) in Depth:(1) Outer 5 %The requirements of 4.3.2.3(1) applyexcept that SRt1shall be multiplied by 0.80 in Eq 1 and 2. Thevalue of 0.80 SRt1shall not be taken as less than 0.50.(2) Next Inner 5 %General slope of grain shall be limitedin accorda
41、nce with the strength requirements of the individuallaminations.4.3.2.6 Density Requirements:Outer 5 %Density requirements shall apply to the fulllength of the piece of lumber. In order to ensure that lumber isnear-average or above specific gravity for the species, visuallygraded tension laminations
42、 shall have a minimum specificgravity of at least 94 % of the recognized species average fromTest Methods D 2555 based on dry weight and volume at 12 %moisture content. The minimum specific gravity of the piece oflumber shall be the average specific gravity of the entire piece.Rate of growth and per
43、centage of latewood requirements fortension laminations shall apply to the full length of lumber.Visual inspection alone is not an acceptable method of deter-mining specific gravity.4.3.2.7 Other Requirements:Outer 5 %Wide-ringed or lightweight pith associatedwood has a pronounced effect on finger j
44、oint strength. Theamount of material not meeting rate of growth and densityrequirements, in combination with compression wood, shall belimited to18 of the cross section of the piece of lumber. Inaddition, for wet service conditions or pressure-treated mem-bers, compression wood is limited to a maxim
45、um of 5 % of thecross section.4.3.3 E-rated Lumber:4.3.3.1 Grading Requirements:Outer 5 %In addition to having the required modulus ofelasticity, E-rated lumber must meet the requirements forvisually graded lumber given in 4.3.2.2, 4.3.2.3(1), and4.3.2.4(1), with the exception of the knot and slope
46、of grainrequirements as given in 4.3.3.3.4.3.3.2 Other Requirements:Outer 5 %Wide-ringed or lightweight pith associatedwood and compression wood are limited in the same manner asfor visually graded lumber, except that there are no densityrequirements. Material not meeting medium grain rate ofgrowth,
47、 in combination with compression wood, shall belimited to18 of the cross section of the piece of lumber. Inaddition, for wet conditions of use or pressure-treated mem-bers, compression wood is limited to a maximum of 5 % of thecross section.4.3.3.3 The portions of the piece not subjected to mechani-
48、cal E measurements shall have visual criteria applied to ensurepiece quality. Edge knots up to the size permitted in the gradeare acceptable. Other knots are limited to the visual require-ments of the bending stress index for which the E-rated lumberis qualified. For tension laminations, the slope o
49、f grain shall notexceed 1:12 and wide-ringed or pith-associated wood andcompression wood is limited as in 4.3.3.2. Medium graingrowth requirements shall be met for Douglas Fir-Larch andSouthern Pine.4.3.4 Tension laminations to meet the requirements identi-fied in 4.3.1 may be qualified by test as an alternative to thegrading criteria of 4.3.2 and 4.3.3. The procedure given inAnnex A1 shall be used.5. Allowable Properties for Glued Laminated TimberMembers5.1 Allowable properties for individual laminations shall beobtained by multiplying the stress index values fro
