1 / 43

Lecture # 20: Engineering Properties of Wood

Lecture # 20: Engineering Properties of Wood. Engineering Properties of Wood. Grain Orientation Density Moisture Temperature Duration, Rate of loading Defects Other Variability MECHANICAL PROPERTIES. Anisotropic Axes of Wood. Terms: Slope of grain Cross grain Diagonal grain

kimama
Download Presentation

Lecture # 20: Engineering Properties of Wood

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture # 20: Engineering Properties of Wood

  2. Engineering Properties of Wood • Grain Orientation • Density • Moisture • Temperature • Duration, Rate of loading • Defects • Other • Variability • MECHANICAL PROPERTIES

  3. Anisotropic Axes of Wood • Terms: • Slope of grain • Cross grain • Diagonal grain • Spiral Grain

  4. Mechanical Properties of Wood • Parallel to the grain • Perpendicular to the grain Modulus of Elasticity Tensile Strength Compressive Strength Flexural Strength Shear Strength • Large Variability

  5. Modulus of Elasticity Parallel to Grain PL 60% Ult Load PL 20 - 50% Ult Load

  6. Tensile Strength

  7. Cell Wall Structure Figure 14.3

  8. Compressive Strength

  9. Compressive Behavior

  10. Localized Buckling

  11. Flexural Strength

  12. Shear Strength Greatest Shear Strength- primary bond Relative sliding of microfibrils - secondary bond 5 to 15 MPa Bundle of straws; 1/4th of the strength  to grain

  13. Grain Orientation

  14. Density (G) G0 = Oven-dry specific gravity MC = Moisture content

  15. Variations in Density

  16. Moisture Content

  17. Moisture Effects on Mechanical Properties

  18. Shrinkage

  19. Typical Shrinkage Values

  20. Duration of Loading

  21. Other Effects

  22. Creep • Creep: The increase in strain or deformation with time under constant stress. Stress Strain Time Time Strain Strain Creep Relaxation Elastic Elastic Time Time

  23. Creep • Creep strain is permanent and: • is much more severe when loaded perpendicular to the grain. • about 50% of elastic strain for seasoned wood that remains dry or unseasoned wood that remains green. • about 3.5 times the elastic component for green wood that is allowed to dry in service. • of plywood at 18% MC is about 3 - 4 times that of specimens at 6% MC.

  24. Creep • creep strain increases in a cyclic moisture environment • an increase in relative humidity from 65 to 80% increases the creep 50%.

  25. Grading

  26. Defects in Wood

  27. Defects in Wood

  28. Knot: Bottom

  29. Knot: Top

  30. Reduction in Strength

  31. Design

  32. Adjustment Factors: Clear Wood

  33. Minimum Strength Ratios

  34. Stress Modification Factors

  35. Duration of Load

  36. Service Condition Note: a moisture content < 15% is dry

  37. Temperature

More Related