Reprogramación celular

LUMBER

8.1 General 54

8.2 Reference Design Values 54 8.3 Adjustment of Reference Design

Values 54

8.4 Special Design Considerations 56

Table 8.3.1 Applicability of Adjustment Factors for

Structural Composite Lumber ... 55

8

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8.1 General

8.1.1 Scope

Chapter 8 applies to engineering design with struc-tural composite lumber. Basic requirements are pro-vided in this Specification. Design procedures and other information provided herein apply only to structural composite lumber conforming to all pertinent provi-sions of ASTM D5456.

8.1.2 Definitions

8.1.2.1 The term “laminated veneer lumber” refers to a composite of wood veneer sheet elements with wood fiber primarily oriented along the length of the member. Veneer thickness shall not exceed 0.25".

8.1.2.2 The term “parallel strand lumber” refers to a composite of wood strand elements with wood fibers primarily oriented along the length of the member. The least dimension of the strands shall not exceed 0.25"

and the average length shall be a minimum of 150 times the least dimension.

8.1.2.3 The term “structural composite lumber” re-fers to either laminated veneer lumber or parallel strand lumber. These materials are structural members bonded with an exterior adhesive.

8.1.3 Identification

When the design procedures and other information provided herein are used, the structural composite lum-ber shall be identified with the manufacturer’s name and the quality assurance agency’s name.

8.1.4 Service Conditions

Reference design values reflect dry service condi-tions, where the moisture content in service is less than 16%, as in most covered structures. Structural compos-ite lumber shall not be used in higher moisture service conditions unless specifically permitted by the struc-tural composite lumber manufacturer.

8.2 Reference Design Values

Reference design values for structural composite lumber shall be obtained from the structural composite lumber manufacturer’s literature or code evaluation report. In special applications where deflection is a critical factor, or where deformation under long-term loading must be limited, the need for use of a reduced modulus of elasticity shall be determined. See Appen-dix F for provisions on adjusted values for special end use requirements.

8.3 Adjustment of Reference Design Values

8.3.1 General

Reference design values (Fb, Ft, Fv, Fc, Fc, E, Emin) shall be multiplied by the adjustment factors specified in Table 8.3.1 to determine adjusted design values (Fb', Ft', Fv', Fc', Fc', E', Emin').

STRUCTURAL COMPOSITE LUMBER

8

Table 8.3.1 Applicability of Adjustment Factors for Structural Composite Lumber

ASD

only ASD and LRFD LRFD

only

Format Conversion Factor Resistance Factor

Load Duration Factor Wet Service Factor Temperature Factor Beam Stability Factor 1 Volume Factor1 Repetitive Member Factor Column Stability Factor Bearing Area Factor

K

F



Time Effect Factor

F

b'

= F

b

x C

D

C

M

C

t

C

L

C

V

C

r

- - 2.54 0.85 

F

t'

= F

t

x C

D

C

M

C

t

- - - - - 2.70 0.80 

F

v'

= F

v

x C

D

C

M

C

t

- - - - - 2.88 0.75 

F

c'

= F

c

x C

D

C

M

C

t

- - - C

P

- 2.40 0.90 

F

c'

= F

c

x - C

M

C

t

- - - - C

b

1.67 0.90 -

E

^'

= E x - C

M

C

t

- - - - - - E

min'

= E

min

x - C

M

C

t

- - - - - 1.76 0.85 -

1. See 8.3.6 for information on simultaneous application of the volume factor, CV, and the beam stability factor, CL.

8.3.2 Load Duration Factor, C

_D

(ASD Only)

All reference design values except modulus of elas-ticity, E, modulus of elasticity for beam and column stability, Emin, and compression perpendicular to grain, Fc, shall be multiplied by load duration factors, CD, as specified in 2.3.2.

8.3.3 Wet Service Factor, C

_M

Reference design values for structural composite lumber are applicable to dry service conditions as specified in 8.1.4 where CM = 1.0. When the service conditions differ from the specified conditions, adjust-ments for high moisture shall be in accordance with information provided by the structural composite lum-ber manufacturer.

8.3.4 Temperature Factor, C

_t

When structural members will experience sustained exposure to elevated temperatures up to 150F (see Ap-pendix C), reference design values shall be multiplied by the temperature factors, Ct, specified in 2.3.3.

8.3.5 Beam Stability Factor, C

_L

Structural composite lumber bending members shall be laterally supported in accordance with 3.3.3.

8.3.6 Volume Factor, C

_V

Reference bending design values, Fb, for structural composite lumber shall be multiplied by the volume factor, CV, and shall be obtained from the structural composite lumber manufacturer’s literature or code

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evaluation reports. When CV  1.0, the volume factor, CV, shall not apply simultaneously with the beam sta-bility factor, CL (see 3.3.3) and therefore, the lesser of these adjustment factors shall apply. When CV > 1.0, the volume factor, CV, shall apply simultaneously with the beam stability factor, CL (see 3.3.3).

8.3.7 Repetitive Member Factor, C

_r Reference bending design values, Fb, shall be mul-tiplied by the repetitive member factor, Cr = 1.04, where such members are used as joists, studs, or similar members which are in contact or spaced not more than 24" on center, are not less than 3 in number and are joined by floor, roof, or other load distributing elements adequate to support the design load. (A load distribut-ing element is any adequate system that is designed or has been proven by experience to transmit the design load to adjacent members, spaced as described above, without displaying structural weakness or unacceptable deflection. Subflooring, flooring, sheathing, or other covering elements and nail gluing or tongue-and-groove joints, and through nailing generally meet these criteria.)

8.3.8 Column Stability Factor, C

_P Reference compression design values parallel to grain, Fc, shall be multiplied by the column stability factor, CP, specified in 3.7.

8.3.9 Bearing Area Factor, C

_b

Reference compression design values perpendicular to grain, Fc, shall be permitted to be multiplied by the bearing area factor, Cb, as specified in 3.10.4.

8.3.10 Pressure-Preservative Treatment

Adjustments to reference design values to account for the effects of pressure-preservative treatment shall be in accordance with information provided by the structural composite lumber manufacturer.

8.3.11 Format Conversion Factor, K

_F

(LRFD Only)

For LRFD, reference design values shall be multi-plied by the format conversion factor, KF, specified in Table 8.3.1.

8.3.12 Resistance Factor,  (LRFD Only)

For LRFD, reference design values shall be multi-plied by the resistance factor, , specified in Table 8.3.1.

8.3.13 Time Effect Factor,  (LRFD Only)

For LRFD, reference design values shall be multi-plied by the time effect factor, λ, specified in Appendix N.3.3.

8.4 Special Design Considerations

8.4.1 Notches

8.4.1.1 The tension side of structural composite bending members shall not be notched, except at ends of members for bearing over a support, and notch depth shall not exceed 1/10 the depth of the member. The compression side of structural composite bending members shall not be notched, except at ends of mem-bers, and the notch depth on the compression side shall not exceed 2/5 the depth of the member. Compression

side end-notches shall not extend into the middle third of the span.

8.4.1.2 See 3.1.2 and 3.4.3 for effect of notches on strength.

WOOD

STRUCTURAL

In document Lic. Camila Vázquez Echegaray (página 38-50)