ASTM D3737-00a
(Practice)Standard Practice for Establishing Allowable Properties for Structural Glued Laminated Timber (Glulam)
Standard Practice for Establishing Allowable Properties for Structural Glued Laminated Timber (Glulam)
SCOPE
1.1 This practice covers the procedures for establishing allowable properties for structural glued laminated timber. Properties considered include bending, tension and compression parallel to the grain, modulus of elasticity, horizontal shear, compression perpendicular to the grain and radial stresses in curved members.
1.2 This practice is limited to the calculation of allowable properties subject to the given procedures for the selection and arrangement of grades of lumber of the species considered.
1.3 Requirements for production, inspection and certification are not included, but in order to justify the allowable properties developed using procedures in this practice, manufacturers must conform to recognized manufacturing standards. Refer to ANSI/AITC AI90.1 and CSA 0122.
1.4 Allowable properties established by use of this practice are based on dry conditions of use (less than 16 % moisture content). Modifications for wet-use conditions are given in 9.2.
1.5 The values stated in inch-pound units are to be regarded as standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D 3737 – 00a
Standard Practice for
Establishing Stresses for Structural Glued Laminated
Timber (Glulam)
This standard is issued under the fixed designation D 3737; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope Grades of Structural Lumber
D 4761 Test Method for Mechanical Properties of Lumber
1.1 This practice covers the procedures for establishing
and Wood-Base Structural Material
allowable design stresses for structural glued laminated timber.
E 105 Practice for Probability Sampling of Materials
Properties considered include bending, tension and compres-
2.2 Other Standards:
sion parallel to the grain, modulus of elasticity, horizontal
ANSI/AITC A190.1 Structural Glued Laminated Timber
shear, and compression perpendicular to the grain.
CSA 0122 Structural Glued Laminated Timber
1.2 This practice is limited to the calculation of design
stresses for glulam subject to the given procedures for the
3. Terminology
selection and arrangement of grades of lumber of the species
3.1 Definitions:
considered.
3.1.1 E-rated lumber—lumber graded for laminating by
1.3 Requirements for production, inspection, and certifica-
nondestructive measurement for a modulus of elasticity (E) and
tion are not included, but in order to justify the design stresses
by visual inspection in accordance with the grading rules of the
developed using procedures in this practice, manufacturer must
applicable grading or inspection agency.
conform to recognized manufacturing standards for glulam.
3.1.2 glulam—a term used to denote structural glued lami-
Refer to ANSI/AITC A190.1 and CSA 0122.
nated timber, which is a material glued up from suitably
1.4 Stresses established by use of this practice are based on
selected and prepared pieces of wood either in a straight or
dry conditions of use (12 % average with less than 16 %
curved form with the grain of all pieces essentially parallel to
moisture content). Modifications for wet-use conditions are
the longitudinal axis of the member.
given in 9.2.
3.1.3 horizontally laminated timber—a glulam member de-
1.5 The values stated in inch-pound units are to be regarded
signed to resist bending loads applied perpendicularly to the
as standard.
wide faces of the laminations.
1.6 This standard does not purport to address all of the
3.1.4 lamination—a layer of lumber within the glued lami-
safety concerns, if any, associated with its use. It is the
nated timber.
responsibility of the user of this standard to establish appro-
3.1.5 modulus of elasticity (E)—for laminating, E is divided
priate safety and health practices and determine the applica-
into two categories to distinguish mode of measurement and
bility of regulatory limitations prior to use.
application.
2. Referenced Documents 3.1.6 long-span E—the E calculated from deflection mea-
sured in a flat-wise test of lumber with a center point loading
2.1 ASTM Standards:
and a span-depth ratio (1/d) of approximately 100.
D 198 Test Methods of Static Tests of Timber in Structural
3.1.7 member E—the design E of the finished glued lami-
Sizes
nated member as defined in this practice.
D 245 Practice for Establishing Structural Grades and Re-
3.1.8 vertically laminated timber—a glulam member de-
lated Allowable Properties for Visually Graded Lumber
signed to resist bending loads applied parallel to the wide faces
D 2395 Test Methods for Specific Gravity of Wood and
of the laminations.
Wood-Base Materials
3.1.9 visually graded lumber—lumber graded by visual
D 2555 Test Methods for Establishing Clear Wood Strength
inspection in accordance with the grading rules of the appli-
Values
cable grading or inspection agency.
D 2915 Practice for Evaluating Allowable Properties for
3.2 Symbols:
This practice is under the jurisdiction of ASTM Committee D7 on Wood and is
the direct responsibility of Subcommittee D07.02 on Lumber and Engineered Wood Annual Book of ASTM Standards, Vol 14.02.
Products. Available from the American Institute of Timber Construction, 11818 S.E. Mill
Current edition approved Sept. 10, 2000. Published November 2000. Originally Plain Blvd., Suite 415, Vancouver, WA 98684.
published as D 3737 – 78. Last previous edition D 3737 – 00. Available from the Canadian Standards Association, 178 Rexdale Blvd.,
Annual Book of ASTM Standards, Vol 04.10. Rexdale, Ontario, Canada, M9W 1R3.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 3737
and suitably marked or segregated.
GDE = ratio of the cross-sectional area of the local grain 4.3 The effect of decay or compression failure upon strength
deviation (which may or may not be associated cannot be readily determined, thus these defects shall be
with a knot) at the edge of the lumber to the prohibited from laminating grades insofar as existing inspec-
tion and grading technology permit. Firm white speck or light
cross-sectional area of the lumber (see Fig. 1).
GDC = ratio of the cross-sectional area of the local grain
white pocket is permissible in grades of lumber that permit
deviation (which may or may not be associated knots to occupy up to one third or more of the cross section
with a knot) away from the edge of the lumber to
provided their extent in combination with knots does not
the cross-sectional area of the lumber (see Fig. 1). exceed that of the largest edge knot permitted. The exception is
GDS = projected sum of all GDE and GDC values within
that firm white speck and light white pocket shall be excluded
a one-foot length of lumber as illustrated in Fig. 1.
from end joints in tension members and the outer 10 % of the
KE = ratio of cross-sectional area of knot at the edge of
total depth on the tension side of bending members.
the wide face of lumber to the cross-sectional area
4.4 Compression wood in readily identifiable and damaging
of the lumber (see Fig. 2).
form shall be limited in laminating grades.
KC = ratio of the cross-sectional area of knot located
4.4.1 For dry conditions of use, grades permitting knots up
away from the edge of the lumber to the cross-
to one half of the cross section may contain streaks of
sectional area of the lumber. When a knot at the
compression wood occupying as much as 20 % of the cross
edge of the wide face and a knot located away
section. Streaks of compression wood up to one eighth of the
from the edge are in the same cross section, the
cross section may be permitted in other grades.
combination of the two shall be used in determin-
4.4.2 For wet conditions of use, or for pressure-treated
ing KC (see Fig. 2).
members, the conditions of 4.4.1 apply except that compres-
SMF = stress modification factor of a beam.
sion wood is limited to 5 % of the cross section in tension
SR = strength ratio of the tension lamination at the
t 1
members and in the outer 10 % of the total depth on the tension
outermost fiber.
side of bending members.
4.5 Lumber shall be free of shakes and splits that make an
4. Requirements for Laminations
angle of less than 45° with the wide face of the piece. Pitch
pockets shall be limited in size to the area of the largest knot
4.1 Separate laminations shall not exceed 2 in. (51 mm) in
permitted, and pitch streaks shall be limited to one sixth of the
net thickness. Lumber may be end-jointed to form any length
width of the lumber.
of lamination or placed edge-to-edge to form any width, or
4.6 For wet-use conditions, significant amounts of wane are
both. Lumber must be edge-glued unless it can be shown by
limited to that which will be removed upon final surfacing of
calculations or experimental data that unglued edge joints meet
the member. For dry-use conditions, wane up to one sixth the
the structural performance requirements of the glulam mem-
width of the lumber is permitted at each edge provided the
bers for the intended use.
allowable shear strength is adjusted to consider this unbonded
4.2 All lumber used shall be graded prior to laminating the
region.
member and suitably marked or segregated to identify its
grade. When pieces are ripped, each piece shall be regraded 4.7 The range of moisture content of lumber for assembly
(a) (b)
GDC = y/b GDC = y/b
GDE = z/b GDE = z/b
GDS = x/b where x=y+z GDS = x/b where x
(a) Example of grain deviations not associated with a knot where the projected (b) Example of grain deviations associated with knots where the projected grain
grain deviations do not overlap. deviations overlap.
FIG. 1 Knot and Grain Deviation Measurement at the Outer 5 % on the Tension Side of a Member Occurring in a 1-ft Length
D 3737
NOTE 1—When edge knots and centerline knots occur at the same cross section, the sum of the edge knots and centerline knots is used in calculating
KC as shown in (b).
FIG. 2 Knot Measurement for the Next Inner 5 % on the Tension Side of a Bending Member
into a single member shall not exceed five percentage points, include the average of the sum of all knot sizes within each 1-ft
except when all of the lumber is 12 % or lower. (0.30-m) length, taken at 0.2-ft (60-mm) intervals, and the
determination of the 99.5-percentile knot size.
5. Knot Data
5.3 Knot data for glulam combinations loaded in compres-
5.1 Data on knot properties for the grades of lumber to be
sion parallel to grain must include the average and the standard
used are needed in order to determine the design levels for the
deviation for the largest knot size within each 3-ft (0.9-m)
bending strength of members loaded perpendicular to the wide
length taken at 0.5-ft (0.15-m) interval.
faces of the laminations (horizontally laminated members),
5.4 Requirements for Evaluation of New Knot Data—New
along with compression parallel to the grain. Two different
knot data is reviewed for acceptance to judge the adequacy of
levels of sampling are recognized for collecting these knot
the new data to better represent the target populations. Where
data, one during development of a laminating grade and
knot values are already in use, new data may be presented to
another during the actual use of grade in production of glulam
substantiate, augment, or replace the existing data. The follow-
members. Guidelines for sampling material are given in
ing requirements must be followed in consideration of the new
Practice E 105.
data. A decision sequence (see Appendix X1) is recommended.
5.1.1 Development—During the development of the lami-
5.4.1 Substantiation—Where new data is demonstrably well
nating grade, not less than 100 pieces or 1000 lineal ft (300 m)
representative of the population, but does not present signifi-
of lumber randomly chosen from a representative group shall
cant differences stated in Appendix X1, and where existing
be used as a sample for each grade of lumber. No special
data is fully documented and not in need of increased preci-
selection of the pieces should be made; the only requirement is
sion, the new data analysis may be considered for inclusion to
that they meet the grade but not qualify for a higher grade.
permanent files as substantiation of the specific knot values to
5.1.2 Use—After the laminating grade has been put in use,
which it applies.
not less than 200 pieces of a grade or 2000 lineal ft (600 m)
5.4.2 Augment Existing Data—Where new data is demon-
shall be randomly chosen in at least 20 sampling visits to
strably well representative of the population, but does not
glulam manufacturers representing at least 75 % of the regional
present significant differences as stated in Appendix X1, and
production of that grade. This type of survey must be con-
where existing data is documented and can be shown to be in
ducted within 3 years of the development survey and used to
need of additional precision, the new data may be combined
modify if necessary, combinations based on the development
with existing data to result in a more precise estimate of the
survey. This second level of sampling should not be considered
respective population parameters.
as effective for longer than 10 years. A change of grading rules
5.4.3 Replacement—Before new knot data may be consid-
involving liberalization of knot size limitation requires resam-
pling. ered for replacement of existing data, appropriate statistical
5.1.3 Base knot measurement on a displacement technique. tests must show that the population was representatively
Measurements shall represent the projected cross-sectional sampled, and that the new data describes the population to be
area of knots as determined by an average width on the wide significantly different from the population represented in cur-
faces, or in the case of edge or spike knots, an estimated rent use with respect to mean, and 99.5 percentile knot size. In
equivalent displacement. the absence of a representative sample, data may be considered
5.1.4 Determine location and width of all knots larger than for replacement on the grounds that it represents a more
⁄4 in. (6 mm) for the lumber in the survey. adequate sample or is more completely documented than
5.2 Knot data for horizontally laminated combinations must existing data, or both.
D 3737
6. Stress Index Values 6.1.5.1 As an alternative to 6.1.5, the horizontal shear stress
index shall be permitted to be determined from flexural tests of
6.1 Visually Graded Lumber—Test Methods D 2555 pro-
full-size beams in accordance with the principles of Test
vide information on clear wood strength properties and their
Methods D 198 with specific loading details as shown in
expected variation for small, clear, straight-grained specimens
Annex A5. Laminating lumber used in the critical core area of
of green lumber. Based on these properties, stress index values
the test beams subjected to maximum shear stresses shall be
are calculated.
selected such that it is representative of the population of
6.1.1 Determine the bending stress index by calculating the
on-grade lumber used in normal production for the species and
clear wood stress fifth percentile in accordance with Test
grade being evaluated. The required number of samples and the
Methods D 2555, multiplying by the appropriate factors in
lower 5th percentile tolerance limit of shear strength shall be
Table 1, and furthermore multiplying by 0.743 to adjust to a
determined in accordance with Practice D 2915 and the analy-
12-in. (0.3-m) deep, uniformly loaded simple beam with a 21:1
sis procedures given in Annex A5. The horizontal shear stress
span-to-depth ratio.
index is
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