Rope testing - A discussion document
Rope testing has been the basis of a number of lengthy discussions between
myself an other people over the last year or more and it has become more
than clear that there are a number or people who do not wholly subscribe
to some of the assumptions on which the tests are based, or who question
whether there are not some other important factors which should also be
the subject of scrutiny in any concerted programme which is aimed at gaining
a better understanding of rope performance for cavers.
The purpose of this brief document is to initiate some discussion on these
topics, and eventually form the basis of a plan of work to investigate them
further.
The current NCA 'state of the art' is the drop test rig which we are using
to determine the breaking strength of new and used caving rope. The drop
test has a number of key features which make it the preferred tool for our
use:
- · relatively cheap
- · simple to use and to understand
- · produces reasonably repeatable results
- · produces reasonably meaningful results.
Over the last few months, a lot of work has gone into the production of
a document to support the last point in particular.
However, there are other factors which are acknowledged to be relevant on
the safe application of ropes in caving, many of which are not evaluated
at all by the simple drop tests we are doing at present, either because
this is not possible with a drop test or because it is not the focus of
current effort. These include:
- · knot strength
- · energy absorption (i.e. the actual forces applied to the caver
in a fall situation)
- · physical/chemical damage to the rope
There are also a number of assumptions on which the rope tests are based
which require validation: primarily the validity of the use of fall factors
which has been questioned by some.
A short 'to do' list for further work might include:
- · literature search to produce a comprehensive bibliography of
rope testing
- · devising of tests to produce actual data on the effect of chemical
attack by common reagents
- · correlation of data from drop tests and 'static' ultimate load
tests
- · investigation of the repeatability of drop tests
The drop test rig itself could be improved to improve the knowledge which
comes from it and its actual useability:
- · addition of facility to plot load curves
- · additional height
- · improved portability.
Clearly investigation of any of the above points will require additional
effort and funding, both of which are scarce. However, they form the next
logical step in the development of our knowledge about ropes and we must
prioritise them in the light of the resources which we do have available.
Nick Williams
November 4, 1997
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