How do trees go from being in the forest, to being a part of my home? How come the palm tree in my yard couldn’t be used for building but the pine tree would be considered structural grade? In this blog, we'll explore how wood gains strength during its growth, how engineers determine its strength for construction purposes, and which types of wood are typically used for structural building members and why.
Table of Contents
- The Growth and Strengthening of Wood
- Determining the Strength of Wood
- Wood for Structural Building Members
- Conclusion
The Growth and Strengthening of Wood
- Cellular Structure: Wood is composed of cellulose fibers, which are strong in tension, and lignin, which acts as a binder and is strong in compression. This composite structure gives wood its unique strength.
- Annual Rings: As a tree grows, it adds a new layer of wood around its circumference each year, known as an annual ring. Each ring consists of a lighter portion (springwood) and a darker portion (summerwood). The springwood is grown rapidly and is less dense, while the summerwood grows slowly and is denser and stronger.
- Heartwood and Sapwood: The inner heartwood is generally older, drier, and stronger than the outer sapwood.
Determining the Strength of Wood
- Grain Direction: Wood is anisotropic, meaning its strength varies with the direction of the grain. It's generally stronger along the grain (lengthwise) than across it.
- Moisture Content: The strength of wood is also influenced by its moisture content. Dry wood is generally stronger and more stable than wet wood.
- Testing Methods: Engineers use various methods to test wood strength, including bending tests, compression tests, and tension tests. These tests help determine properties like modulus of elasticity (stiffness), bending strength, and compressive strength.
Wood for Structural Building Members
- Common Structural Woods: Softwoods like pine, spruce, and fir are commonly used for structural purposes due to their availability, cost-effectiveness, and good strength-to-weight ratio. Hardwoods like oak and maple are also used, especially where higher strength or aesthetic appeal is needed.
- Strength Grading: Wood used in construction is often strength graded. This process involves evaluating the wood for defects (like knots) and categorizing it based on its strength and stiffness.
Conclusion
Wood's unique cellular structure, combined with the way it strengthens as it grows, make it both strong and adaptable. Rogall + Co. has over 20 years of experience working with all types of wood, from structural grade timber to cosmetic wood crafted pieces. We can help you determine what wood is best for your project.
