Taking the Measure of Wood: How to determine who's the strongest?
Updated: Jul 28, 2020
Summary: All things being equal, stronger materials tend to produce stronger results.
Plantation eucalyptus is stronger than domestic USA hardwoods. Why is stronger better? All things being equal, stronger materials tend to produce stronger results. Strong timbers come from strong species. All things being equal – and you should check this with your own engineers – an 8” eucalyptus mat = 9.25” oak mat in terms of bending strength.
For mat users stronger results generally mean better mat life and less disruptions in the field because of a failed mat.
How can we measure that one wood material (species) is stronger than another wood material? Fortunately, three very well-respected organizations have done the heavy lifting and provide a huge amount of reliable data.
There are two American standards and one European standard for reliable data.
The US Forest Service Forest Products Laboratory (FPL) publishes the definitive sourcebook for wood species. The Wood Handbook: Wood as an Engineering Material is available free here. Chapter Five shows testing data for all domestic and Canadian woods and many imported species including eucalyptus.
The second source, the American Wood Council, publishes their National Design Specifications for Wood Construction (NDS) as well as a Supplement that lists most North American woods and their working characteristics (for example, bending strength, compressive strength, and others). Much of the NDS data originates with the FPL data.
The (excellent and simple) Eurocode 5 specification classifies wood strength into general wood classes, where higher is better. For example, European Oak, which itself is stronger than American Oak, is class D30. Eucalyptus is class D40.
Most of the data on the web, for example, www-wood-database.com comes from the FLP.
The two images below show what kind of data you might expect to see from the FPL Wood Handbook and the AWC National Design specifications.
But there is one essential difference between the data. The FPL data are testing data. The NDS and Eurocode data are design specifications using the same data, with safety factors applied for real use calculations. Those safety factors are applied to answer questions such as, “How big does a post need to be to hold up a roof?”.
If you are looking at comparing two different mats, for example, mixed hardwood to eucalyptus or oak to eucalyptus then any of the standards will work.
But, if you are doing anything with an engineering requirement then you need to use design specifications. Your engineering department already knows this.
See link for the appropriate values to use in engineering.