ASTM D7568-23

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D7568 − 23
Standard Specification for
Polyethylene-Based Structural-Grade Plastic Lumber for
Outdoor Applications
This standard is issued under the fixed designation D7568; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope* fillers, reinforcements, and additives. Each formulation is to be
identified as a distinct and different product, to be tested and
1.1 This specification covers a type of plastic lumber
evaluated separately.
product, defined as polyethylene-based structural-grade plastic
lumber (SGPL), for use as main framing members, including 1.8 Diverse and multiple combinations of both virgin and
joists, stringers, beams, columns; and secondary framing recycled polyethylene material systems are permitted in the
members, including planking, posts and bracing; in outdoor manufacture of SGPL products.
structures such as decks, boardwalks, docks, and platforms.
1.9 Fiber reinforcements used in SGPL include manufac-
1.2 This specification is applicable to solid, rectangular tured materials such as fiberglass (chopped or continuous),
SGPL products where polyethylene resin (non cross-linked) is carbon, aramid and other polymeric materials.
the continuous phase and is at least 50 % of the product (by
1.10 A wide variety of chemical additives are typically
weight).
added to SGPL formulations. Examples include colorants,
1.3 This specification is not applicable to plastic lumber chemical foaming agents, ultraviolet stabilizers, fire retardants,
products containing cellulosic materials as additives, fillers or lubricants, anti-static products, heat stabilizers, and coupling
fiber reinforcements. agents.
1.4 SGPL products covered by this specification shall not be 1.11 Diverse types and combinations of filler systems are
used as tensile members. permitted in the manufacturing of SGPL products. Fillers that
cause the product to fail the requirements of 6.13 are not
1.5 SGPL products are produced using several different
permitted in the manufacturing of SGPL products.
manufacturing processes. These processes utilize a number of
polyethylene resin material systems that include varying pro- 1.12 In order for a product to be classified as SGPL, it must
portions of fillers, fiber reinforcements, and other chemical meet the minimum stress and modulus criteria consistent with
additives. the specific product as marked, and additionally the properties
specified in Section 6 of this specification.
1.6 Due to thermodynamic effects that result in outer-
surface densification during manufacture, SGPL products are 1.13 This specification pertains to SGPL where any rein-
typically non-homogeneous in the cross-section. This standard forcement is uniformly distributed within the product. When
does not address materials that have been modified from their reinforcement is not uniformly distributed, the engineering
original cross-section. issues become substantially more complex. For this reason,
1.6.1 The cross-section non-homogeneity is addressed in such products are not covered in this document.
the material property assessments in this document only for
1.14 Products that fail at strains of less than 0.02 (2 %)
applications in which the product cross-section is not modified
when tested in flexure in accordance with 6.6 are not compat-
by cutting, notching, or drilling. For products modified in this
ible with the underlying assumptions of Annex A1 and are
manner, additional engineering considerations are required and
beyond the scope of this standard (see Note 1).
they are beyond the scope of this document.
NOTE 1—Calculation of time-dependent properties in Annex A1 is
1.7 For purposes of this standard, an SGPL product is a
based on the assumption that the product does not fail in a brittle manner.
specific combination of polyethylene resin, together with
The 2 % strain limit was selected based on the judgment of the task group
members that created Annex A1.
1.15 This specification addresses issues relevant to a buy-
1 er’s requirements for SGPL products and has therefore been
This specification is under the jurisdiction of ASTM Committee D20 on
Plastics and is the direct responsibility of Subcommittee D20.20 on Plastic Lumber. developed in the format of a procurement specification.
Current edition approved Feb. 1, 2023. Published February 2023. Originally
1.16 Criteria for design are included as part of this specifi-
approved in 2012. Last previous edition approved in 2017 as D7568 – 17.
DOI:10.1520/D7568-23. cation for SGPL products.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7568 − 23
1.17 Use of SGPL members in application will typically 2.3 Other Documents:
require the design of structural connections. Connection design ASCE 7 Minimum Design Loads for Buildings and Other
Structures
between SGPL members falls outside the scope of this stan-
dard.
3. Terminology
1.18 The values are stated in inch-pound units, as these are
3.1 Definitions of Terms:
currently the most common units used by the US construction
3.1.1 For definitions of terms used in this specification
industry. Equivalent SI units are indicated in parentheses.
associated with plastics issues refer to the terminology con-
1.19 This standard does not purport to address all of the
tained in Terminology D883. For definitions of terms used in
safety concerns, if any, associated with its use. It is the
this specification and associated with fire issues refer to the
responsibility of the user of this standard to establish appro-
terminology contained in Terminology E176.
priate safety, health, and environmental practices and deter-
3.1.2 plastic lumber, n—a manufactured product made pri-
mine the applicability of regulatory limitations prior to use.
marily from plastic materials (filled or unfilled), typically used
as a building material for purposes similar to those of tradi-
NOTE 2—There is no known ISO equivalent to this standard.
tional lumber, which is usually rectangular in cross-section.
1.20 This international standard was developed in accor-
(Terminology D883)
dance with internationally recognized principles on standard-
3.1.2.1 Discussion—Plastic lumber is typically supplied in
ization established in the Decision on Principles for the
sizes similar to those of traditional lumber board, timber and
Development of International Standards, Guides and Recom-
dimension lumber; however the tolerances for plastic lumber
mendations issued by the World Trade Organization Technical
and for traditional lumber are not necessarily the same.
Barriers to Trade (TBT) Committee.
(Terminology D883)
3.1.3 resin, n—a solid or pseudo solid organic material often
2. Referenced Documents
of high molecular weight, which exhibits a tendency to flow
2.1 The following documents of the issue in effect on the
when subjected to stress, usually has a softening or melting
date of product purchase form a part of this specification to the
range, and usually fractures conchoidally (Terminology D883).
extent referenced herein:
3.1.3.1 Discussion—In a broad sense, the term is used to
2 designate any polymer that is a basic material for plastics.
2.2 ASTM Standards:
3.1.4 thermoplastic, n—a plastic that repeatedly can be
D883 Terminology Relating to Plastics
softened by heating and hardened by cooling through a
D2344/D2344M Test Method for Short-Beam Strength of
temperature range characteristic of the plastic, and that in the
Polymer Matrix Composite Materials and Their Laminates
softened state can be shaped by flow into articles by molding
D2915 Practice for Sampling and Data-Analysis for Struc-
or extrusion (Terminology D883).
tural Wood and Wood-Based Products
D6108 Test Method for Compressive Properties of Plastic
3.2 Definitions of Terms Specific to This Standard:
Lumber and Shapes
3.2.1 bulge, n—convex distortion (away from the center of
D6109 Test Methods for Flexural Properties of Unreinforced
the cross-section) of the face of the product from a straight line
and Reinforced Plastic Lumber and Related Products
drawn from edge to edge across the width.
D6112 Test Methods for Compressive and Flexural Creep
3.2.2 crook, n—distortion of the product in which there is a
and Creep-Rupture of Plastic Lumber and Shapes
deviation in a direction perpendicular to the edge from a
D6341 Test Method for Determination of the Linear Coef-
straight line from end to end along the length.
ficient of Thermal Expansion of Plastic Lumber and
3.2.3 cup, n—concave distortion (towards the center of the
Plastic Lumber Shapes Between –30 and 140°F (–34.4
cross-section) of the face of the product from a straight line
and 60°C)
drawn from edge to edge across the width.
D6662 Specification for Polyolefin-Based Plastic Lumber
Decking Boards
3.2.4 edge, n—the side of a rectangular-shaped product
D7032 Specification for Establishing Performance Ratings
corresponding to the thickness.
for Wood-Plastic Composite and Plastic Lumber Deck
3.2.5 face, n—the side of a product corresponding to the
Boards, Stair Treads, Guards, and Handrails
width.
E84 Test Method for Surface Burning Characteristics of
3.2.6 reinforcement, n—a material added to the thermoplas-
Building Materials
tic resin to improve its mechanical properties.
E176 Terminology of Fire Standards
3.2.7 self-supporting specimen, n—a specimen that remains
in place by its own structural characteristics both before and
during a fire test.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available from American Society of Civil Engineers (ASCE), 1801 Alexander
the ASTM website. Bell Dr., Reston, VA 20191, http://www.asce.org.
D7568 − 23
3.2.8 structural grade plastic lumber, n—a solid, rectangu- 5.4 Width—Unless otherwise specified in 4.1.8, product
lar reinforced thermoplastic composite lumber product manu- width shall be:
factured for load-bearing applications such as joists, beams, or For members less than 3 in. in nominal width the tolerance
3 1
columns in outdoor structures. on width shall be + ⁄16 /– ⁄16 inch.
3.2.9 test set, n—a full complement of test specimens Nominal (in.) Actual (in.) Tolerance(in.)
1 3 1
3 2 ⁄2 + ⁄16 / - ⁄16
required for a specific assessment.
1 3 3
4 3 ⁄2 + ⁄16 / - ⁄32
3.2.9.1 Discussion—As an example, a test set for flexural 1 3 3
6 5 ⁄2 + ⁄16 / - ⁄32
1 3 1
8 7 ⁄4 + ⁄16 / - ⁄8
properties (see 6.6.3) requires 28 test specimens.
1 3 1
10 9 ⁄4 + ⁄16 / - ⁄8
3.2.10 thickness, n—the lesser dimension of the cross- 1 1 5
12 11 ⁄4 + ⁄4 / - ⁄32
sectional profile of a rectangular-shaped product.
For members greater than 12 in. in nominal width the
1 5
3.2.11 width, n—the greater dimension of the cross-
tolerance on width shall be + ⁄4 / - ⁄32 inch.
sectional profile of a rectangular-shaped product, or the dimen-
5.5 Length—Unless otherwise specified in 4.1.7, products
sion of the cross-sectional profile of a square product.
up to 20 ft shall have tolerances of 6 ⁄2 inch. Over 20 feet the
tolerances shall be 6 ⁄2-in. per 20-ft of length or fraction
4. Ordering Information
thereof. Measurement of lengths shall be made at 23 6 2°C
4.1 The information contained in this specification is in- (73.4 6 4°F) and relative humidity of 50 6 5 %.
tended to be helpful to producers, distributors, regulatory
5.6 Flatness Tolerance—Products shall be flat with a maxi-
agencies and users including designers, architects, and engi-
mum cup or bulge in the face limited to the tolerances in Table
neers. The information will also promote understanding be-
1 and Table 2. Linear interpolation of the values is acceptable
tween purchasers and sellers. The purchaser shall state whether
for dimensions other than listed.
this specification is to be used, select the preferred options
TABLE 1 Cup or Bulge Tolerances Relative to Nominal Width (2x)
permitted herein, and include the allowable design information
Face Width, in. #4 in. 6 in. 8 in. 10 in. 12 in.
in the invitation to bid and purchase order from the following:
1 3 1 3 1
Tolerance (±) ⁄16 in. ⁄32 in. ⁄8 in. ⁄16 in. ⁄4 in.
4.1.1 Title, number and date of this specification,
TABLE 2 Cup or Bulge Tolerances Relative to Nominal Size
(square)
4.1.2 Minimum allowable bending stress and apparent
bending stiffness, Size, in. #4 in. 6 in. 8 in. 10 in. >12 in.
3 1 3 1 1
Tolerance (±) ⁄32 in. ⁄8 in. ⁄16 in. ⁄4 in. ⁄4 in.
4.1.3 Percent recycled content (if requested),
4.1.4 Flame spread index,
5.7 Squareness—Unless a specially shaped member is
4.1.5 Color, specified, the cross-section of all structural-grade plastic lum-
ber products shall be perpendicular (that is, 90 degree angle
4.1.6 Quantity in lineal feet,
4.1.7 Cut length, from face to edge of a square or rectangular shape and suited
for the intended purpose).
4.1.8 Cross-sectional dimensions,
4.1.9 Packing requirements,
5.8 Crook—Crook shall conform to the tolerances in Table
4.1.10 Palletization, if required,
3. Linear interpolation of the values is acceptable for dimen-
4.1.11 Marking, if other than specified.
sions other than listed.
6. Performance Requirements
5. Dimensions and Permissible Variations
6.1 Load Combinations: Plastic members subject to mul-
5.1 It is permissible to produce SGPL either in sizes that are
tiple load types shall be checked for all applicable load
similar to the standard dimensions of the wood industry, or to
combinations. Load factors and load reductions shall be
other dimensions designated by manufacturers or buyers. This
determined in accordance with the applicable code or ASCE 7.
specification does not limit the dimensional range of produc-
All applicable load combinations shall be evaluated to deter-
tion.
mine the critical load combination to be used in design.
5.2 Use of a licensed Professional Engineer is recom-
mended for designing and selecting SGPL products in accor- NOTE 3—Application of load duration factors to load combinations in
which each load has a different associated duration is a complex process
dance with this specification.
and varies depending on whether the design engineer is using allowable
5.3 Thickness—Unless otherwise specified in 4.1.8, product stress design (ASD) or load and resistance factor design (LRFD) meth-
odology. A conservative design approach applies the load duration factor
thickness tolerance shall be:
For members less than 2 in. in nominal thickness the
3 1
tolerance on thickness shall be + ⁄16 / - ⁄16 .
TABLE 3 Crook Tolerances Relative to Nominal Length and Width
Nominal (in.) Actual (in.) Tolerance (in.) Length in Feet #4 in. 6 in. 8 in. 10 in. 12 in.
1 3 1
2 1 ⁄2 + ⁄16 / - ⁄16 Width Width Width Width Width
1 3 1 3 1 3 3 3
3 2 ⁄2 + ⁄16 / - ⁄16 4-6 ⁄8 in. ⁄4 in. ⁄16 in. ⁄16 in. ⁄16 in.
1 1 3 3 3
1 3 3
4 3 ⁄2 + ⁄16 / - ⁄32 8 ⁄2 in. ⁄2 in. ⁄8 in. ⁄8 in. ⁄8 in.
1 3 3 3 5 1 1 1
5 4 ⁄2 + ⁄16 / - ⁄32 10 ⁄4 in. ⁄8 in. ⁄2 in. ⁄2 in. ⁄2 in.
7 13 13 13
1 3 1
12 1 in. ⁄8 in. ⁄16 in. ⁄16 in. ⁄16 in.
6 5 ⁄2 + ⁄16 / - ⁄8
1 1
14 1- ⁄4 in. 1- ⁄8 in. 1 in. 1 in. 1 in.
For members greater than 6 in. in nominal thickness the
1 3 1 1 1
16 1- ⁄2 in. 1- ⁄8 in. 1- ⁄8 in. 1- ⁄8 in. 1- ⁄8 in.
3 1
tolerance on thickness shall be + ⁄16 /- ⁄8 inch.
D7568 − 23
equal to the longest duration in the applicable load combination. More
6.6.1 The test procedure shall be in accordance with Test
refined approaches for specific applications can be found in the technical
Methods D6109 with the following modifications:
literature.
6.6.1.1 The specimens for flexural members shall be tested
6.2 Design Properties:
in the joist configuration (Method B in Test Methods D6109)
6.2.1 All members shall be designed such that for all load
unless it is shown that the minimum properties in the plank
combinations:
configuration also hold for the joists and that there is no size
effect for the product.
f # F ' × C (1)
a n D
6.6.2 SGPL Requirements—SGPL shall meet or exceed the
where:
following criteria:
f = total applied stress in each combination (psi)
a
6.6.2.1 The mean value of the secant flexural modulus
F ' = allowable stress as calculated in 6.6.3.2, 6.7.2, 6.8.2.1,
n
minus one standard deviation of the value at 1 % outer fiber
6.8.3.1, or 6.9.3.2 (psi)
strain shall equal or exceed 200,000 psi at 23 6 2°C (73.4 6
C = Load Duration Factor for the material and considered
D
4°F) and 50 6 10 % RH.
load duration. Derivation of C is explained in Annex
D
6.6.2.2 The mean, minus two standard deviations, value of
A2.
the flexural stress F at 3 % outer fiber strain shall equal or
bt
6.3 Interpolation of Properties:
exceed 2,000 psi at 23 6 2°C (73.4 6 4°F). If any SGPL
6.3.1 Interpolation of mechanical properties of a SGPL product fails prior to reaching 3 % strain, then the mean, minus
product from test data from the same product at other width
two standard deviations, of the flexural stress at failure for that
dimensions is permitted if the test results verify a logical product shall equal or exceed 2,000 psi.
progression of properties and the following conditions are met:
NOTE 5—The typical mode of failure for SGPL members results from
6.3.1.1 All specimens have the same thickness and material
flexure by excessive strain rather than by rupture. Thus, the requirement in
composition.
the standard flexural test is to define the failure stress as the stress at 3 %
strain, if rupture has not occurred before that point.
6.3.1.2 Three or more test sets are performed on specimens
with varying width.
6.6.3 Allowable Flexural Properties:
6.3.1.3 At least one test set is performed on specimens with
6.6.3.1 Specimens Tested—A minimum of 28 specimens
a width greater than that of the product whose properties are
shall be tested at 23 6 2°C (73.4 6 4°F). Specimens selected
being interpolated.
for testing shall be representative of typical production and
6.3.1.4 At least one test set is performed on specimens with
shall be selected to include sources of potential variability.
a width less than that of the product whose properties are being
6.6.3.2 Allowable Flexural Stress—The allowable flexural
interpolated.
stress, F ', of a product is given as follows (see temperature
b
tolerances in 6.6.3.1):
6.4 Creep Rupture:
6.4.1 Creep Rupture tests shall be performed for the in-
F ' 5 ~F /FS!*C *C (2)
b b TF L
tended use (that is, flexural test for a flexural member,
where:
compression test for a compression member) in accordance
F = the base flexural stress value at 23°C (73.4°F) for
with the procedures outlined in Test Methods D6112. b
normal duration loading (10 yr. duration), (psi), which
6.4.2 F shall be the stress required to cause creep rupture
cr
is defined as follows:
in ten years determined from the creep rupture curve calculated
in Test Methods D6112.
F 5 F *β # F (3)
b bt cr
6.4.3 E shall be the effective ten-year modulus determined
cr
where:
from the creep rupture curve calculated in Test Methods
F = the non-parametric 5 % lower tolerance limit at 75 %
bt
D6112.
confidence of the flexural stress at 3 % outer fiber
6.4.4 The combined effect of time (that is, creep rupture)
strain (or failure if 3 % strain cannot be reached)
and temperature determined by Test Methods D6112 shall be
determined from flexure tests conducted in accor-
compared against the product of C and β. The more
TF
dance with Section 6.6.1 (psi). Statistical calculations
conservative result shall form the basis of design.
shall be in accordance with Practice D2915. F shall
bt
6.5 Serviceability: meet the requirements of 6.6.2
F = ultimate creep rupture stress for flexure calculated in
6.5.1 Deflection shall be calculated using the apparent
cr
accordance with 6.4, (psi)
modulus of elasticity determined in 6.6.3.3. Calculated deflec-
β = Stress-time factor to convert the test value, F , to a
tion shall not exceed applicable code or project specific bt
ten-year normal duration value. This value shall be
deflection limits.
determined in accordance with Annex A1.
6.5.2 The maximum ten-year strain in any member shall not
FS = factor of safety = 2.5,
exceed 0.03 (3 %).
C = temperature factor for flexure determined in accor-
TF
NOTE 4—It is possible that some applicable codes or project specific
dance with Annex A3
requirements will require deflection limits that result in a maximum strain
C = beam stability factor determined using principles of
L
of less than 0.03.
engineering mechanics.
6.6 Flexural Members: NOTE 6—Discussion of beam stability is provided in X1.2.
D7568 − 23
6.6.3.3 Apparent Modulus of Elasticity and Adjustment for where:
Creep—The apparent modulus of elasticity, E', shall be deter-
F = the non-parametric 5 % lower tolerance limit at 75 %
vt
mined as follows:
confidence of the shear stress at 3 % fiber strain (or
failure if 3 % strain cannot be reached) determined
E' 5 E*C /α # E (4)
TE cr
from shear tests conducted in accordance with 6.7.1
where:
(psi). Statistical calculations shall be in accordance
E = modulus as determined from Test Methods D6109,
with Practice D2915.
except that it represents the chord modulus values
F = ultimate creep rupture stress for shear calculated in
cr
between 0.1 F and 0.4 F , (psi) accordance with 6.4, (psi)
bt bt
E = the effective ten-year stiffness determined in accor-
β = stress-time factor to convert the test value, F , to a ten
cr v
dance with 6.4, (psi)
year normal duration value. This value shall be
C = temperature factor for modulus determined in accor-
determined in accordance with Annex A1.
TE
dance with Annex A3
6.8 Bearing:
α = creep adjustment factor determined in accordance
6.8.1 Tests shall be performed in accordance with Test
with Annex A1.
Method D6108 with the following modifications:
NOTE 7—An example problem for the case of uniform loading on a
6.8.1.1 Specimens Tested—A minimum of 28 specimens
single span joist is described in Appendix X4.
shall be tested at 23 6 2°C (73.4 6 4°F). Specimens selected
6.6.3.4 For uniform loading at an average ambient tempera-
for testing shall be representative of typical production and
ture of 90°F the maximum total deflection of the structural-
shall be selected to include sources of potential variability.
grade plastic lumber product including the effect of creep shall
6.8.1.2 Bearing Perpendicular to the Direction of Extru-
not exceed L/180 or as otherwise specified by the applicable
sion:
code.
(1) Test Method D6108, Subsection 6.2: The standard test
specimen shall take the form of the actual manufactured
6.7 Shear Properties:
product cross-section with a length equal to half its width.
6.7.1 Test Procedure—Test Method D2344/D2344M incor-
(2) Test Method D6108, Subsection 10.2: Place the test
porating the following criteria and modifications:
specimen between the surfaces of the compression platens,
6.7.1.1 Specimen Size for Testing—Specimens for test shall
taking care to align the center line of the surface perpendicular
not be machined to reduce the cross-sectional thickness—only
to the extrusion with the center line of the platens to ensure that
full-size cross sections shall be used. Also, in accordance with
the ends of the specimen are parallel with the surface of the
subsection 5.3 of Test Method D2344/D2344M, span length-
platens. The proper positioning of a member with dimensions
to-specimen thickness ratio of 4 shall be used for the specimen b × d is shown in Fig. 1. Adjust the crosshead of the testing
size.
machine until it just contacts the top of the compression platen.
6.8.1.3 Bearing Parallel to the Direction of Extrusion:
6.7.1.2 Specimens Tested—A minimum of 28 specimens
shall be tested. Specimens selected for testing shall be repre-
sentative of typical production and shall be selected to include
sources of potential variability.
6.7.1.3 An extension indicator shall be affixed to the speci-
men to record the displacement (strain) of the specimen below
the upper loading nose as a function of applied stress. The
recorded stress-strain data shall also be reported.
6.7.1.4 Use the short beam stress, F , as calculated in
sbs
Equation (1) of Test Method D2344/D2344M as the shear
stress value F in Equation (9) below.
v
6.7.2 Allowable Shear Stress—The allowable shear stress of
a product is given as follows:
F ' 5 ~F /FS!*C (5)
v v TF
where:
F = the base shear stress value at 23°C (73.4°F) for
v
normal duration loading (10-year duration), (psi)
defined below,
FS = factor of safety = 2.5,
C = temperature factor for flexure, determined in accor-
TF
dance with Annex A3
F , the base shear stress value for the product is determined
v
as follows:
FIG. 1 Bearing Perpendicular to the Direction of Extrusion Platen
F 5 F *β # F (6) Centerline
v vt cr
D7568 − 23
(1) Test Method D6108, Subsection 6.2: The standard test where:
specimen shall take the form of the actual manufactured
F = the non-parametric 5 % lower tolerance limit at 75 %
C'
t
product cross-section with a width equal to twice its length.
confidence of the bearing stress perpendicular to the
(2) Test Method D6108, Subsection 10.2: Place the test
extrusion direction at 3 % fiber strain (or failure if
specimen between the surfaces of the compression platens,
3 % strain cannot be reached) determined from
taking care to align the center line of the surface parallel to the
bearing tests conducted in accordance with 6.8.1
extrusion with the center line of the platens to ensure that the
(psi). Statistical calculations shall be in accordance
ends of the specimen are parallel with the surface of the
with Practice D2915.
platens. The proper positioning of a member with dimensions
F = the ultimate creep rupture stress for bearing perpen-
cr
b × d is shown in Fig. 2. Adjust the crosshead of the testing
dicular to the direction of extrusion calculated in
machine until it just contacts the top of the compression platen.
accordance with 6.4, (psi)
6.8.2 Bearing Perpendicular to Extrusion: β = stress-time factor to convert the test value, F , to a
C'
t
6.8.2.1 Allowable Bearing Stress—The allowable bearing
ten year normal duration value. This value shall be
stress, F ', of a product loaded in compression perpendicular determined in accordance with Annex A1.
C'
to the extrusion direction is given as follows (see temperature
6.8.3 Bearing Parallel to Extrusion:
tolerances in 6.8.1.1):
6.8.3.1 Allowable Bearing Stress—The allowable bearing
F ' 5 ~F /FS!*C (7)
stress, F ', of a product loaded in compression parallel to the
C' C' TC
Ci
extrusion direction is given as follows:
F = the base bearing stress value at 23°C (73.4°F), (psi)
C'
F ' 5 F /FS *C (9)
~ !
defined below, Ci Ci TC
FS = factor of safety = 2.5,
where:
C = temperature factor for compression, determined in
TC
F = the base bearing stress value at 23°C (73.4°F), (psi)
Ci
accordance with Annex A3,
defined below
F , the base bearing stress value for the product is
C' FS = factor of safety = 2.5,
determined as follows:
C = temperature factor for compression, determined in
TC
accordance with Annex A3,
F 5 F *β # F (8)
C' C' cr
t
F , the base bearing stress value for the product is deter-
ci
mined as follows:
F 5 F *β # F (10)
Ci Ci cr
t
where:
F = the nonparametric 5 % lower tolerance limit at 75 %
Ci
t
confidence of the bearing stress parallel to the extru-
sion direction at 3 % fiber strain (or failure if 3 %
strain cannot be reached) determined from bearing
tests conducted in accordance with 6.8.1 (psi). Statis-
tical calculations shall be in accordance with Practice
D2915.
F = ultimate creep rupture stress for compression parallel
cr
to the direction of extrusion calculated in accordance
with 6.4, (psi)
β = stress-time factor to convert the test value, F , to a
Ci
t
ten year normal duration value. This value shall be
determined in accordance with Annex A1.
6.9 Compression Members:
6.9.1 Test Procedure—Test Method D6108.
6.9.1.1 Specimens Tested—A minimum of 28 specimens
shall be tested at 23 6 2°C (73.4 6 4°F). Specimens selected
for testing shall be representative of typical production and
FIG. 2 Bearing Parallel to the Direction of Extrusion Platen Cen-
terline shall be selected to include sources of potential variability.
D7568 − 23
6.9.2 SGPL Requirements—SGPL shall meet or exceed the
C = column stability factor determined using principles
p
following criteria:
of engineering mechanics
6.9.2.1 The mean minus one standard deviation value of the NOTE 10—Discussion of column stability is provided in X1.2.
secant compression modulus at 1 % strain shall equal or exceed
6.10 Combined Stresses:
120,000 psi at 23 6 2°C (73.4 6 4°F) and 50 6 10 % RH.
6.10.1 Bending and Compression—Plastic members subject
6.9.2.2 The mean, minus two standard deviations, value of
to both axial compression and flexure shall be proportioned
the compressive stress F at 3 % strain shall equal or exceed
ct using principles of engineering mechanics.
1,500 psi at 23 6 2°C (73.4 6 4°F) and 50 6 10 % RH. If any
NOTE 11—Discussion of combined stresses is provided in X1.2.
SGPL product fails prior to reaching 3 % strain, then the mean,
6.10.2 Structures expected to experience significant side
minus two standard deviations, of the stress at failure for that
sway shall not be used unless appropriate engineering proce-
product shall equal or exceed 1,500 psi.
dures or tests are employed in the design of such members to
NOTE 8—Often the compression modulus and stress values of SGPL are
ensure that all applied loads will be safely carried by the
significantly lower than the flexural modulus and stress values.
members.
6.9.3 Design of Compression Members:
6.11 Dimensional Stability—Thermal Expansion:
6.9.3.1 SGPL compression members shall meet the follow-
6.11.1 The value of the coefficient of thermal expansion
ing slenderness ratio limitation:
shall be calculated in accordance with the test procedure
S 5 K L /r,28 (11) outlined in Test Method D6341 with the following modifica-
r u
tions:
where:
6.11.1.1 Specimens Tested—A minimum of 15 specimens
S = slenderness ratio,
r
shall be tested to establish an average value. Report the
K = buckling length coefficient (greater than or equal to 1.0)
measured coefficient of thermal expansion in the longitudinal
that depends on the end constraint for the column.
or the transverse direction to two significant figures for use in
L = unbraced length of the member, (in.)
u
design calculations.
r = radius of gyration (in.)
6.11.2 Thermal expansion shall be considered for the design
The above slenderness ratio shall be checked for both
of expansion slots or any other case where movement due to
principle bending axes of the member.
thermal effects will cause structural or serviceability concerns.
Specimens selected for testing shall be representative of typical
NOTE 9—This slenderness ratio limitation has been used by SGPL
production and shall be selected to include sources of potential
manufacturers in the past. Due to the broad range of products covered by
this standard, designers are cautioned to check all compression members variability.
for potential buckling using the properties of the product being used.
6.12 Weatherability:
Discussion of column stability is provided in Appendix X1.2. Specific
6.12.1 SGPL products that are exposed to solar radiation
discussion of column slenderness ratio is provided in X1.2.7.4
shall meet the requirements of subsection 6.3.2 of Specification
6.9.3.2 The allowable compressive stress, F ', of a product is
c
D6662.
given as follows:
NOTE 12—The testing requirements of subsection 6.3 of Specification
F ' 5 ~F /FS!*C *C (12)
c C TC p
D6662 can only identify products with the potential to deteriorate in less
than two years under outdoor conditions. However, the results from
where:
testing of plastic lumber decking boards after eleven years of outdoor
F = the base compressive stress value at 23°C (73.4°F) for
C
exposure have shown that the boards had discolored and faded, but that
normal duration loading (10 yr. duration), (psi) as
both strength and stiffness were basically unchanged. Similar results are
defined below, expected with SGPL. Further details of this testing and results are given
in Appendix X3 in Specification D6662
F 5 β*F # F (13)
C ct cr
6.13 Hygrothermal Cycling:
where:
6.13.1 Test Procedure—Specimens shall also be prepared as
F = the non-parametric 5 % lower tolerance limit at 75 %
described in Test Methods D6109. Each specimen shall then be
ct
confidence of the compressive stress at 3 % fiber
weighed to the nearest 0.00022 lb (0.1 g). Specimens shall then
strain determined from compression tests conducted
be totally submerged underwater (using weights to hold down,
in accordance with 6.9.1 (psi). Statistical calculations
if necessary) for a period of 24 hours. After removal from
shall be in accordance with Practice D2915. F shall
water, each specimen shall then be dried with a dry cloth on the
bc
meet the requirements of 6.9.2.
outside surfaces and weighed again within 20 minutes. The
F = ultimate creep rupture stress for compression calcu-
cr specimens shall then be frozen to –20 (6 5)°F (-29 (6 2)°C)
lated in accordance with 6.4, (psi)
for 24 hours, then returned to room temperature. The above
β = stress-time factor to convert the test value, F , to a
ct
process completes one hygrothermal cycle.
ten year normal duration value. This value shall be
6.13.2 The procedure in 6.13.1 shall be repeated two more
determined in accordance with Annex A1,
times, for a total of three cycles of water submersion, moisture
FS = factor of safety = 2.5,
absorption equilibrium, and freezing. After completion of these
C = temperature factor for compression, determined in
TC
steps, the specimens shall be returned to room temperature and
accordance with Annex A3,
tested as described in Test Methods D6109.
D7568 − 23
6.13.3 Specimens Tested—A minimum of 15 specimens 8. Workmanship
shall be prepared in accordance with Test Methods D6109 and
8.1 The structural-grade plastic lumber products furnished
tested. Specimens selected for testing shall be representative of
in accordance with this specification shall be an acceptable
typical production and shall be selected to include sources of
match to approved samples in pattern, color, and surface
potential variability.
appearance. The products shall be free of defects that adversely
6.13.4 Criteria—Any obvious physical changes that occur
affect performance or appearance. Such defects include
as a result of the hygrothermal cycling shall be noted. The
blemishes, spots, indentations, cracks, blisters, and breaks in
flexural modulus and the greater of the stress level at 3% strain
corners or edges.
or the stress at fracture as defined in Test Methods D6109 shall
9. Product Technical Data Sheet
retain 90 % of the mean value when tested without hygrother-
9.1 The manufacturer shall provide the following informa-
mal cycling in accordance with 6.6.3.2.
tion for each product:
6.14 Flame Spread Index:
9.1.1 Flexural properties as determined in 6.6.
6.14.1 The flame spread index of SGPL products shall be
9.1.2 Shear properties as determined in 6.7.
determined by testing in accordance with Test Method E84.
9.1.3 Bearing properties as determined in 6.8.
6.14.2 A minimum of five test specimens shall be tested.
9.1.4 Compression properties as determined in 6.9.
6.14.3 The test specimens shall either be self-supporting by 9.1.5 Temperature adjustment factors for flexural stress and
their own structural characteristics or held in place by added modulus in accordance with Annex A3.
supports along the test specimen surface. The test specimen 9.1.6 Temperature adjustment factor for compression in
shall remain in place throughout the test duration. Test results accordance with Annex A3.
are invalid if one of the following occurs during the test: (a) the 9.1.7 Stress-time adjustment factor, β, for flexure in accor-
test specimen sags from its position in the ceiling to such an dance with Annex A1.
extent that it interferes with the effect of the gas flame on the 9.1.8 Creep adjustment factor, α, for flexure in accordance
test specimen or (b) portions of the test specimen melt or drop with Annex A1.
to the furnace floor to the extent that progression of the flame 9.1.9 Ten-year modulus in accordance with 6.4.3.
front on the test specimen is inhibited. 9.1.10 Load duration factors for range of time periods in
accordance with Annex A2.
6.14.4 Appendix X1 of Test Method E84 provides guidance
9.1.11 Creep rupture value for stress, F in accordance with
on mounting methods.
cr
6.4.2.
6.14.5 Products shall have a flame spread index no greater
than 200 when tested in accordance with Test Method E84.
10. Quality Assurance
10.1 A quality assurance program shall be employed to
NOTE 13—For combustible construction, codes often require fire
performance at least equivalent to that of wood. A maximum flame spread
verify compliance with specific portions of this specification.
index of 200 when tested in accordance with Test Method E84 is
11. Packaging and Packing
considered to be equivalent to that of wood. For outdoor applications,
there is no requirement specified for smoke developed index.
11.1 The products shall be packaged in accordance with
NOTE 14—Fire retardants are available to increase the resistance to
normal commercial practice and packed to assure acceptance
ignitability and flame spread of SGPL and shall be incorporated as needed.
by common carrier and to provide protection against damage
during normal shipping, handling, and storage.
7. Specimen Conditioning
12. Keywords
7.1 Conditioning of Specimens for Tests—Unless specifi-
cally stated otherwise, all specimens shall be conditioned and 12.1 plastic lumber; polyethylene; recycled plastics; rein-
tested in accordance with the appropriate test method. forced; structural grade composite lumber
ANNEXES
(Mandatory Information)
A1. DERIVATION OF ALPHA AND BETA FACTORS AND CREEP CURVES
A1.1 The procedures in this annex were developed based on demonstration bridges and railroad tie applications. However,
testing of a specific formulation of structural grade plastic during development of this standard, committee members
lumber. They provide one method for determination of adjust- expressed the need to expand the experimental backup data to
ment factors for time-dependent properties. These procedures include a wider range of formulations. This process is currently
have been used successfully to support designs of several underway.
D7568 − 23
5 4 3 2
A1.2 The following method shall be used to calculate α, β, m σε 5 C 1C 1C 1C 1C
~ !
0.03 % 5ε 4ε 3ε 2ε 1ε
0.03 % 0.03 % 0.03 % 0.03 % 0.03 %
and development of creep curves based on short-term experi-
(A1.5)
mental data. This procedure is based on a Rutgers University
A1.2.4 Procedure for determining ten-year failure stress and
thesis titled “Time Dependence of the Mechanical Properties of
for predicting creep - The steps outlined in A1.2.4.2 through
an Immiscible Polymer Blend” by Jennifer Lynch dated
A1.2.4.4 for determining stress, together with the steps out-
October 2002. For use in design, these values shall be
lined in A1.2.4.5 through A1.2.4.9 for predicting creep are
compared against the creep-rupture factors determined in
iterative processes. These steps shall be performed using
accordance with Test Methods D6112 and the more conserva-
tive shall apply. mathematical computer software capable of performing nu-
merical iterations.
A1.2.1 Perform five constant strain rate tests at ε = 3 % ⁄min
´
A1.2.4.1 Procedure for determining ten-year failure stress
in accordance Test Methods D6109. Continue the test until 5 %
strain or until rupture. Record all data at the same time interval
A1.2.4.2 For each of the 30 SED values calculated in
for all tests. Determine the average values of load, deflection,
A1.2.3.1 calculate the predicted stress at ten years with the
stress, strain, and strain energy density (SED= σε) for each
equation:
time interval recorded. If the coefficient of variation at any time
m~σε!
σ 5 σ /min* ε´ /ε´ (A1.6)
~ !
10 0.03 % 10 0.03 %
interval is greater than 8 % increase the number of specimens
in accordance with subsection 3.4.2 of Practice D2915 until the
where:
coefficient of variation is less than 8 %. Fit fifth order polyno-
σ /min = stress from 0.03 % ⁄min test for a particular
0.03 %
mial regression curves for stress versus time and SED versus
SED value.
strain.
ε´ = ε /(5,256,000 min)
10 f
5 4 3 2
m(σε) = m as a function of SED calculated in A1.2.3.4,
σ3 % t 5 A t 1A t 1A t 1A t 1A t (A1.1)
~ !
5 4 3 2 1
and
5 4 3 2
SED ~ε! 5 B ε 1B ε 1B ε 1B ε 1B ε (A1.2)
3 % 5 4 3 2 1
ε = the lesser of 0.03 or the strain corresponding to
f
the creep rupture strain, F calculated in 6.4.
where:
cr
A and B = regression constants for each curve.
x x
A1.2.4.3 For the 30 predicted stress values fit a fifth order
A1.2.2 Repeat the procedure outlined in A1.2.1 for a strain polynomial regression curve for stress versus strain:
rate of ε = 0.03 % ⁄min. Provide all test data and regression
´
5 4 3 2
σ ~ε! 5 D ε 1D ε 1D ε 1D ε 1D ε (A1.7)
10 5 4 3 2 1
curves required by A1.2.1.
where:
Discussion—It is permitted to use strain rates other than
those recommended in A1.2.1 and A1.2.2 provided that the
D = regression constants, and
x
strain rate of A1.2.1 is approximately 100 times the strain rate ε = SED/σ
of A1.2.2. For the remainder of this procedure ε´3 % and
A1.2.4.4 Calculate the failure stress at ten years by substi-
ε´0.03% are left as variables to allow the use of alternate strain
tuting ε into Eq A1.7:
f
rates.
σ 5 σ ~ε ! (A1.8)
f,10 10 f
A1.2.3 Procedure for determining the rate relation exponent
function m (σ ε ):
0.03% where:
A1.2.3.1 Select 30 SED values such that the interval be-
ε = the initial failure strain estimate,
f
tween values is equal and the largest value is equal to the
ε = defined below for the first iteration, and
fi
largest SED from the 0.03 % ⁄min strain rate test. Each SED
ε = defined in A1.2.4.9 for all subsequent iterations.
f,c
value shall be calculated using the following equation:
ε 5 ε /2 * 11n (A1.9)
~ ! ~ !
fi f c
SED 5 SED *i/30 (A1.3)
~ !
i max,0.03 %
where:
where:
ε = the lesser of 0.03 or the strain corresponding to the
f
i = 1 through 30.
creep rupture strain, F , calculated in 6.4,
cr
n = an initial estimate of the creep exponent = 0.05
A1.2.3.2 For both the 0.03 % ⁄min test and the 3 % ⁄min test c
determine the strain for each SED value calculated in A1.2.3.1
A1.2.4.5 Procedure for predicting creep:
using Eq A1.3. Calculate stress (σ = SED ⁄ε ) and time (t = ε ⁄ε´)
A1.2.4.6 Equate the average stress of the 3%/min test with
for each SED value.
σ calculated in A1.2.4.4 and solve for t as follows:
f,10 r1
A1.2.3.3 For each SED value, determine a value of m, as
t
r1
given by the following equation:
* σ ~t!dt
3%
σ ~t ! 5 5 σ (A1.10)
ε t
3% r1 ave f,10
r1
0.035 %
dt
log *
S D
ε
3 %
m 5 (A1.4)
ε´
3 %
where:
log
S D
ε´
0.035 %
σ (t) is as calculated in A1.2.1.
3%
A1.2.4.7 Equate the average stress of the 0.03%/min test
A1.2.3.4 From the 30 calculated m values, fit a fifth order
polynomial regression curve: with σ calculated in A1.2.4.4 and solve for t as follows:
f,10 r2
D7568 − 23
t
r2
n shall be within 5 % of n calculated in A1.2.4.8.
c,test c,predicted
* σ ~t!dt
0.03%
If the difference is greater than 5 %, recalculate ε in A1.2.4.9
σ ~t ! 5 5 σ (A1.11) f,c
0.03% r2 ave t f,10
r2
dt
* using n and σ in A1.2.4 with the recalculated ε . Repeat
c,test f,10 f,c
the creep test at a constant stress equal to the recalculated σ .
f,10
where:
This shall be repeated until n is within 5 % of n .
c,test c,predicted
σ (t) is as calculated in A1.2.2.
0.03%
A1.2.6 Calculate β:
A1.2.4.8 Solve for the creep exponent n as follows:
c
β 5 σ /F (A1.15)
ε f,10 bt
0.03 %
log
S D
ε
3 % where:
n 5 (A1.12)
c
t
r1
F = experimental flexural stress as described in 6.6.3.2,
bt
log
S D
t
r2
(psi)
σ = the failure stress determined after sufficient iterations
f,10
where:
performed in accordance with A1
...