Bending strength

What is bending strength?

Bending strength, also known as flexural strength, describes the ability of wood to resist bending stress without breaking. Bending strength is an important measure for the load-bearing capacity and stiffness of wooden components and is expressed in newtons per square millimeter (N/mm²).

Flexural strength - diagram © by Hugo Kämpf

Determination of bending strength

The determination of bending strength is carried out using a bending test. A wooden beam of defined length and cross-sectional dimensions is clamped between two supports and loaded in the middle with a force until it fails. The bending strength is calculated from the breaking load and the geometric parameters of the wooden beam.

Influencing factors

The bending strength of wood is significantly influenced by various factors:

• Wood species: Generally, woods with higher density also have higher bending strength.
• Moisture content: Dry wood exhibits greater bending strength than moist wood.
• Defects and weaknesses: Knots, cracks, and growth defects in the wood can significantly reduce its bending strength.
• Load direction: Bending strength is much greater along the grain than perpendicular to the grain.

Application

Knowledge of bending strength is crucial for the calculation and construction of wooden components. It plays an important role in the dimensioning of beams, columns, boards, and other load-bearing elements.

Example values:

• Oak: approx. 60-120 N/mm²
• Spruce: approx. 50-136 N/mm²
• Beech: approx. 60-210 N/mm²

Standards:

• DIN 4071-1: Structural timber – Grading based on strength classes
• DIN EN 338: Timber construction – Strength classes for structural timber and wood products

Simply explained

Imagine a wooden beam that bends without breaking. Bending strength shows how much force the wood can withstand before breaking. The higher the bending strength, the more force the wood can take.