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Wood Moisture Content Compressive Strength

Reference data and engineering information about wood moisture content compressive strength for material properties applications.

woodmoisturecontentcompressive

Overview

Engineering reference data for Wood Moisture Content Compressive Strength in material science and properties.

Key Formulas

Stress

σ=FA\sigma = \frac{F}{A}

Force per unit area.

Strain

ε=ΔLL0\varepsilon = \frac{\Delta L}{L_0}

Change in length per original length.

Hooke's Law

σ=Eε\sigma = E \varepsilon

Stress proportional to strain in elastic region.

Thermal Expansion

ΔL=αL0ΔT\Delta L = \alpha L_0 \Delta T

Length change due to temperature.

Variables

Symbol Description Unit
σ\sigma Stress Pa
ε\varepsilon Strain —
EE Young's modulus Pa
α\alpha Thermal expansion coefficient 1/°C
ΔT\Delta T Temperature change °C

Moisture Content Data

The following table summarizes typical moisture content ranges for various wood species relative to their maximum compressive strength (at 2% moisture).

Wood Species Condition Moisture Content (%) Relative Strength vs. 2% MC
Red Spruce Air Dried 14% ~70-75%
Red Spruce Kiln Dried 6% ~95-98%
Longleaf Pine Green Wood 20% ~50-55%
Douglas Fir Green Wood 24% ~40-45%

Note: Relative strength values are approximate and interpolated from the general trend described.

Strength Calculation

The compressive strength parallel to grain of wood decreases as its moisture content increases above the reference point of 2% moisture.

General Formula

The adjusted strength range based on a given moisture content is calculated as:

Adjusted Strength=Base Strength Range×Reduction Factor\text{Adjusted Strength} = \text{Base Strength Range} \times \text{Reduction Factor}

Example: Red Spruce at 16% Moisture

From the provided example for Red Spruce at 16% moisture content (reduction factor = 0.5):

Base Strength Range:

  • Lower Bound: 18 MPa (2610 psi)18 \text{ MPa} \ (2610 \text{ psi})
  • Upper Bound: 39 MPa (5655 psi)39 \text{ MPa} \ (5655 \text{ psi})

Reduced Strength Calculation:

Lower Boundadjusted=18 MPa×0.5=9 MPa (1305 psi)\text{Lower Bound}_{\text{adjusted}} = 18 \text{ MPa} \times 0.5 = 9 \text{ MPa} \ (1305 \text{ psi}) Upper Boundadjusted=39 MPa×0.5=19.5 MPa (2828 psi)\text{Upper Bound}_{\text{adjusted}} = 39 \text{ MPa} \times 0.5 = 19.5 \text{ MPa} \ (2828 \text{ psi})

Therefore, the compressive strength range for Red Spruce at 16% moisture is 9 - 19.5 MPa (1305 - 2828 psi).

Definitions

  • Moisture Content (MC): The weight of water in wood expressed as a percentage of the oven-dry weight of the wood.
  • Reduction Factor: A multiplier (between 0 and 1) used to adjust the reference compressive strength for wood at a specific moisture content above 2%. The factor is determined from strength vs. moisture content charts or equations for a given wood species.

References