Cable suspended structures

[AlfredDFW]

I have a cable suspended roof, with open anchor sockets and the cables are structural galvanized helical strands . The roof has valleys and ridges; it's kind of odd but the cables anchored at the ridges have some rusting (right now I don't know how severe it is)all along their length; the cables anchored at the valleys don't appear to be rusted. I have the folowing questions:
1. Do you have ideas why the rusted ones are at the ridges and the non-rusted at the valleys?
2. Is there some kind of treatment of rusted cables and coating?
3. What is what the industry regulary does to maintain the cables against rusting.

 

[ishvaaag]

1. As long as both are exposed in the outer surface, abrasion by wind is the more likely cause, upon bigger degradation of the galvanization. Higher variation of stress for the particular structure, and then delamination of the zinc cover may be also concomitant.

2. The solution needs be proposed after careful study of the situation and alternatives and not merely after appreciation of the existence of the problem. So one needs to devise means of ascertaining what kind of measures can be needed for the betterment of the roof, and the feaseability of the proposals. If rust as it is likely may have penetrated unseen parts of the cables and the safety of the same becomes doubtful, maybe entire replacement may be needed, what can be awful work for cable supported structures. On maybe even less cycles than the ones allowing for the defects present, the lift industry obliges changing the cabling.

3. I would say that for cables that have shown already the problem, at least annual inspections should be instated.

 

[Sparweb]

Is it possible that the cables attached to the ridges are made differently? Are you sure those cables came from the same source as the cables attached to the valleys? Were they all made at the same time? Were they all made with the same materials? Different spools of cable...? Were they made on-site, or in a shop, or at a number of different shops (ie. changed contractor half-way through the project)? There are many potential reasons why two items that look identical at a distance will turn out to have different properties when seen up close. A careful inspection is warranted.


STF

 

[hokie66]

My guess would be that the cables are exposed to contaminants in the atmosphere which lead to corrosion, but the ones in the valleys are better cleaned by runoff.