N D S 2018 3 10 Bending Members Bearing
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  3. Beams
  4. N D S 2018 3 10 Bending Members Bearing

NDS 2018 Section 3.10 Bending Member - Bearing

The scope of this module is to calculate the sawn lumber beam bearing capacity. The building code subsections required include:

  • NDS 2018 Section 3.2 Bending Members - General
  • NDS 2018 Section 3.10 Design for Bearing
  • NDS 2018 Section 4 Sawn Lumber
  • NDS 2018 Supplement Table 4B and 4D Adjustment Factors and Reference Design Values

Assumptions and limitations

  • ASD method
  • Douglas Fir only
  • Simply supported beam
  • Rectangular section, not notched or tapered
  • Bearing perpendicular to grain
  • Minimum bearing length 3”
  • Beam stability requirements in NDS 2018 Section 4.4.1.2 must be met
  • Beam sizes limited to 6”, 8”, 10”, 12”, 14”

Design Codes

  • AWC-NDS (2018), National Design Specification (NDS) for Wood Construction 2018 Edition. American Wood Council, Leesburg, VA.
  • AWC-NDS (2021), National Design Specification (NDS) Supplement: Design Values for Wood Construction 2018 Edition. American Wood Council, Leesburg, VA.

Inputs parameters

Design Geometry Input

  • b[in]: Rectangular dimension 1.
  • d[in]: Rectangular dimension 2.
  • lbe [in]: Bearing length at each end, set minimum equals to 3.5”

Material Properties Input

Take Fcp from Reference Design Values

Compression perpendicular to grain reference design value

  • \(F_cp [psi]\) : Compression perpendicular to the grain

Wood adjustment factors

Take these parameters from Adjustment Values

  • \(C_M \) : Wet service factor. Recommended value: 1 for moisture content less than 19% for an extended time period. Refer to (2018 NDS, 2018) - Section 4.3.3 for more information.

  • \(C_t \) : Temperature factor. Recommended value: 1 for not exposed to temperatures larger than 150 F. Refer to (2018 NDS, 2018) - Section 4.3.4 for more information.

  • \(C_i \) : Incising factor. Recommended value: 1 for not incised. Refer to (2018 NDS, 2018) - Table 4.3.8 for more information.

  • \(C_b \) : Bearing area factor. Refer to (2018 NDS, 2018) - Section 3.10.4

  • \( C_b = \frac{L_{be} + 0.375}{L_{be}} \)

Calculations

Adjusted bearing capacity

Adjusted perpendicular compression stress \( F'_{cp} [psi] \) is calculated as below:

  • \( F'_{cp} = F_cp \cdot C_M \cdot C_t \cdot C_i \cdot C_b \)

Bearing Strength

Bearing Capacity \( B_n [kip] \)

  • \( B_{n} = F'_{cp} \cdot b \cdot L{be} \)

Output Results

  • Bearing Strength [psi]

References

2018 NDS. (2018). American Wood Council. https://awc.org/publications/2018-nds/

2018 NDS Supplement. (2021). American Wood Council. https://awc.org/publications/2018-nds-supplement/

Breyer, D. E., Cobeen, K. E., & Martin, Z. (2017). Design of Wood Structures ASD/LRFD Eighth Edition. https://shop.iccsafe.org/design-of-wood-structures-asd-lrfd-eighth-edition.html

Validation

Several validations were performed: