Ring Loading is a clear expression. Thank you, Agent Smith, for providing this topic. Thank you for sharing your difficulty finding definition of this important concept. It is understandable that you would have no good experience with this term as it seems to be an idiom only common in American English. I have been familiar with this term for decades, as it has been used in the entertainment industry. Others in the forum have caught on to the meaning and you should as well, once you have been shown correct usage.
The paradigm case for this term is that of a fixed loop that is trusted for a load all in line with the standing line, but then this same fixed loop is seen as capable of slipping or breaking with the addition of a significant transverse load.
In the event production industry, the use of knots is widespread. For the most part, there are expectations that commonly shared knots will be used. For example, all sandbags hoisted overhead on hand lines shall be tied with the bowline knot. If an object taken out overhead cannot use the bowline, such as when taking out a service cable, then the clove hitch is likely used. When neither a fixed loop or a hitch is suitable, such as with a box shape, this is when one might see someone attempt something nonstandard like wrapping the loop of a bowline knot around such an object. The cordage will ?ring? around the box, perhaps even crossing itself to make a ?box wrap.? This is a real time problem that invites the succinct warning, ?You are going to ring load that knot.? The warning is that the knot may slip or break because of the added transverse tension and that there is a risk of a catastrophic failure. The expression is a fair warning and serves the purpose exactly.
The usage then extends away from cordage ringing an object to other cases, never leaving the primary condition of a fixed loop that can fail with transverse tension. Consider a heavy object to be hauled out, a breasting line to be attached which will be used to pull the object out of the plumb line. If the heavy object is hauled out on a bowline knot and the breast line is attached through the fixed loop, then there is the possibility of a transverse tension on the loop. Again, the warning is that the knot may be ring loaded and catastrophic failure could be the consequence.
Agent Smith, your attempts to understand this concept by looking for a knot tied around a circular object are too narrowly focused in asking for some specific shape to provide the important condition and your objections are not well placed for not seeing the central issue, that of a knot that is otherwise trusted but not when a transverse load is added.
Consider the many knots that may be cinched around circular objects. These knots are called hitches. If they may fail, they are not said to be ring loaded as you define the term. They are called unsecure hitches.
Agent Smith, you are critical of our fellow forum members who find the expression ?ring loading? unproblematic. They share the use of the expression with purpose but you somehow think they don?t or shouldn?t Perhaps this common use of language that is accepted by an entire industry and several forum members is unacceptable to you because you have a more exacting analysis.
To this exacting purpose, Agent Smith, you bring vocabulary from hydraulics into the discussion. The terms that you list, longitudinal load, radial load, circumferential load, these are the mutually orthogonal vectors of cylindrical coordinates. Since each of the three illustrations from you, for the three vector directions, point in just one direction, outward, I am not sure you have the concept. You say that these are further considerations that need to be included to understand ?ring loading? or similar phenomena. It could be asked, why bring in hydraulics? Why not analyze knots and rigging for the tensile structures that they are?
It is surprising, as you present yourself as a professional in the use of rigging, that from your opening statement of your thread, you show an inexplicable view of how forces work in knots. You open this topic by saying that ring loading should not be understood on the model of a bend which is pulled apart by a load because in the model of ring loading, as you say, the load is diminished to one half for each leg of the fixed loop. But your assumption is only suitable for the simple case where the load on the fixed loop is hanging down, in one direction, where there is no deflection, where there is no ring loading! If there is any deflection, such as in any bridle, then the load in each leg is more than half the load. Indeed, if the bridle is shallow or if the fixed loop is ring loaded, then the tension in each leg can greatly exceed the weight of the object to be hoisted. This phenomenon situates both the relevance and the significance of the term, ?ring loading,? in the avoidance of catastrophic failure. This is so fundamental to industrial rigging that it calls into question your experience. Have you never installed a rigging point across a span? If you had, you should have felt the transverse component of the load. You would have known how dramatically this force increases with the shallowness of the bridle. This would have figured into your calculations of a safe working load. It is the same phenomenon within a ring loaded knot.
Agent Smith, thank you again for this important topic and thank you for all of your work in and out of this forum. I am glad to be able to contrast my views on knots with your views. I welcome a reply to this or any of my remarks.
