ASD/LRFD Manual - American Wood Council

56 M8: STRUCTURAL COMPOSITE LUMBER
M8.3 Adjustment of Reference Design Values
Member design capacity is the product of reference
design values, adjustment factors, and section properties.
Reference design values for SCL are discussed in M8.2.
Adjustment factors are provided for applications
outside the reference end-use conditions and for member
configuration effects as specified in NDS 8.3. When one
or more of the specific end use or member configuration
conditions are beyond the range of the reference conditions,
these adjustment factors shall be used to modify the
appropriate property. Adjustment factors for the effects of
moisture, temperature, member configuration, and size are
provided in NDS 8.3. Additional adjustment factors can
be found in the manufacturer’s product literature or code
evaluation report. Table M8.3-1 shows the applicability of
adjustment factors for SCL in a slightly different format
for the designer.
Certain products may not be suitable for use in some
applications or with certain treatments. Such conditions
can result in structural deficiencies and may void manufacturer
warranties. The manufacturer or code evaluation
report should be consulted for specific information.
Table M8.3-1
Applicability of Adjustment Factors for Structural Composite
Lumber 1
Allowable Stress Design
F b ′ = F b C D C M C t C L C V C r
F t ′ = F t C D C M C t
F v ′ = F v C D C M C t
F c⊥ ′ = F c⊥ C M C t C b
F c ′ = F c C D C M C t C P
Load and Resistance Factor Design
F b ′ = F b C M C t C L C V C r K F φ b λ
F t ′ = F t C M C t K F φ t λ
F v ′ = F v C M C t K F φ v λ
F c⊥ ′ = F c⊥ C M C t C b K F φ c λ
F c ′ = F c C M C t C P K F φ c λ
E′ = E C M C t E′ = E C M C t
E min ′ = E min C M C t
E min ′ = E min C M C t K F φ s
1. See NDS 8.3.6 for information on simultaneous application of the volume factor, C V , and the beam stability factor, C L .
Bending Member Example
For fully laterally supported members stressed in
strong axis bending and used in a normal building environment
(meeting the reference conditions of NDS 2.3 and
8.3), the adjusted design values reduce to:
For ASD:
F b ′ = F b C D C V
F v ′ = F v C D
F c⊥ ′ = F c⊥ C b
E′ = E
For LRFD:
F b ′ = F b C V K F φ b λ
F v ′ = F v K F φ v λ
F c⊥ ′ = F c⊥ C b K F φ c λ
Axially Loaded Member Example
For axially loaded members used in a normal building
environment (meeting the reference conditions of NDS 2.3
and 8.3) designed to resist tension or compression loads,
the adjusted tension or compression design values reduce
to:
For ASD:
F c ′ = F c C D C P
F t ′ = F t C D
E min ′ = E min
For LRFD:
F c ′ = F c C P K F φ c λ
F t ′ = F t K F φ t λ
E min ′ = E min K F φ s
E′ = E
American Wood Council