Decay of lumber

Evaluating Decay

Many ropes courses have been exposed to the outdoors now for many years. Operators and inspectors have to identify decay of lumber built in.

Decay has been the cause of some accidents. If poles break, it can cause severe accidents.

The community discusses this topic very intensely.

I wanted to conduct a first little test how people can identify rotten lumber – only by tapping with a hammer.

Test assembly:

I took three round logs with 12 cm diameter. They had different stages of decay. 7 people had to give a rating. (4 „experts“ who deal professionally with decay of ropes courses and 3 „normal“ people.

Then I made a pull test with the 3 samples plus one with a well stored piece of lumber.

The 3 samples:

• Sample „bad“ (see picture above): very rotten.
• Sample „medium“: clear signs of decay, but less than sample „bad“.
• Sample „new“: looked new and sounded new, but was exposed to the outdoors for a couple of years.

I asked the question: Please rate the breaking force (in percentage of a not-exposed piece)

Tool:

Tapping with a hammer. The sound was very different between the 3 samples.

The pull test was conducted with 50 cm pieces, loaded in the middle until it failed.

Results

	„Bad“	„medium“	„new“
Breaking load	8 kN	24 kN	46 kN

If you convert this to the rung of a giant ladder (3 meters, divide by 6):

	„bad“	„medium“	„new“
Breaking load converted to 3 meters rung	1,3 kN	4,0 kN	7,7 kN

The very rotten rung („bad“) would be in a dangerous range, the other rungs would withstand the load.

Interesting the comparison to a sample not exposed, stored for 15 years under a roof:

It could hold 110 kN - 11 tons!

This very high breaking load was surprising.

As a rung you could load it with 1,8 tons – in the middle.

Here are the ratings („How many percent of the breaking load of a not exposed piece will hold the samples?“):

Name	„bad“	„medium“	„new“
Experte 1	30%	60%	95%
Experte 2	30%	15%	100%
Experte 3	40%	60%	90%
Experte 4	20%	30%	80%
Nichtexperte 1	20%	40%	80%
Nichtexperte 2	50%	30%	90%
Nichtexperte 3	30%	50%	70%
Maximum	50%	60%	100%
Minimum	20%	15%	70%
% of the unexposed sample	7,27%	22%	42%

No one had an idea of breaking loads of such pieces of round lumber. So they just estimated the percentage. And they were quite far away from the real loads.

However, all test persons identified the difference between lumber with no signs of decay and samples with signs of decay, and significantly reduced breaking load.

As inspector or operator you are facing a digital decision: Discard or use it one more year. This question was not asked and leads to further research.

Tob e continued.