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.
