Welding steel cable? 1

[SteelPE]

I have to go look at a job tomorrow where a client just had a horizontal cable rail installed on his deck. He stepped on one of the cables (I have no idea why) and it broke. He doesn't have confidence in the system anymore and he us bringing me in to look at it. He is saying that the ends of the cable are welded to a nut at each end and I'm wondering if welding steel cable like this is even possible w/o causing a problem? I know they make special adjustable ends for these systems, why one was not used i do not know.

FYI, I did not design the original system and I am being brought in after the face.

 

[MikeHalloran]

Wire rope is not intended to be melted or welded.

Old school termination involves threading the rope end through a steel cone, spreading the wires, and pouring molten zinc into the conical cavity.

New school termination, industrial style, involves folding the rope over a thimble and securing the bitter end to the standing part with, typically, two wire rope clips. The thimble is then secured to a shackle or other end fitting.
The assembly is always ugly.

New school termination, sailboat style, involves swaging or threading some sort of end fitting over the bitter end. The wires may or may not be spread during assembly. You will probably want to visit a sailboat rigging shop to see what is possible for a residential installation.

You might consider including some very stiff compression springs in your cable assemblies, to allow enough deflection to limit the force applied by the next adult who steps on the rope.



Mike Halloran
Pembroke Pines, FL, USA

 

[msquared48]

Either that, or allow the stupid adult to kill himself. Problem, the adult, solved.

Mike McCann
MMC Engineering

 

[hokie66]

MikeH is correct. Wire rope is connected mechanically, not by welding.

 

[oldestguy]

Looks like fixing it will not look so good. Chances are the wires are rusted inside and really not worth using any more. Why not look to plastic coated or galvanized chain, say with links about 3/16" size. Are there any local codes that should be followed?

 

[IFRs]

If I stepped on it and it broke, I would not have any confidence in it either.
I'd call that a reality check, and the wire failed under a small load.

 

[SteelPE]

I did not design this job. I was just asked to look at the system after it was installed. Everything I can find says that there should be mechanical connectors. I am going to find out in about 2 hours what the installer did.

I understand the customers concerns, however, these systems are not meant to be stepped on. The Building Code requires infill parts of railings to support 50# over a 1 square foot area (not 50psf) with the infill not spaced greater than 4" o.c. My interpretation of this is that the wire can not spread more than 4" apart under a 5# load on a 4" dia sphere. If we were to put springs on the end to allow for flex of the cable we wold be in violation of the building code.

 

[dhengr]

SteelPE:
Some building depts. do not allow these types of railing systems, although they do look sexy. The thinking being... instead of providing a safe, properly spaced (balusters), adequately strong railing system; they actually provide the rungs of a ladder for children to climb on, and over the top. You’ll find that when a 200# man stands on one of these cables, he is imparted a far greater (than his weight) tension in the cable, and getting large cable deflections too. When all the cables are properly tensioned, it is almost impossible to design the end posts to take the tension from all of the cables. Then you should also include the code req’rd. loadings on the posts, plus the potential loading your guy applied by stepping on the cable. I believe that most serious installers of these types of cable railing systems, do have swagging equipment as part of their tool kit. They cut the cable to length, thread it through the posts, and apply the last piece of tensioning hardware by swagging it onto the cable.

 

[MikeHalloran]

I'm talking about die springs, not screen door springs. ... so it would take a lot more than 5# of force to push a ball through.

But, given your customer's experience, it's probably better to just install some seriously fat cables.




Mike Halloran
Pembroke Pines, FL, USA

 

[chicopee]

To MikeHolloran's reply "Old school termination involves threading the rope end through a steel cone, spreading the wires, and pouring molten zinc into the conical cavity.", this is not an old school termination since it is used on winding drum and traction type elevators. The thing to keep in mind is when you heat the Babbitt to a molten state so that it can be poured in the socket, you must also heat up the socket otherwise the molten babbitt will chill. Efficiency of such termination is 100%.

 

[SteelPE]

dhengr,

I am being brought in to look at the existing conditions, whether or not the system is allowed is up to the architect.

The existing system used 1/4" dia bolts that were welded to the cable. The bolts were threaded through the steel angle with a cap nut applied to the finish end. Not much room for adjustment. Plus the cable/weld was ground smooth to fit through the hole in the steel angle. It took minimal effort to pass a softball through the cables. In fact you would easily pull two cables together with on hand. No effort had been made to pretension the cable properly. By my calculations, you would need a pretension force of 300#/cable in order for the system to work properly. Then there is the matter of the support posts which probably do not work.

Now I need to write a report with my findings.

 

[miningman]

Chicoppe's notation as to modern day usage of molten zinc etc is definitely true.. When I enter a cage at the top of a 4 or 6000 foot deep shaft , you better believe I have 100% confidence in the methods the rope is attached to the shaft conveyance. I believe epoxy resins are now replacing the use of zinc, and Crosby clamps still have their place.

 

[SteelPE]

Thank you for the help guys. Here is a picture of the anchorage used onsite. Not a good detail at all as the wire is welded and the detial allows for minimal field adjustment.

 

[dhengr]

SteelPE:
It sounds/looks like you have some sort of a home made system which is supposed to look something like the several, more well developed and tested, cable systems which are on the market. If you used a regular nut first, on the bolt, and then cut the bolt a little long, once the tensioning was achieved, you could still put the cap nut on as a finish and locking device. Of course, you can melt a bolt and some cable together with a welding rod, there is just no way to assure the quality of that bonding (weld?). I have seen the ends of cables welded, or fused together by flame cutting, but this was primarily to prevent them from un-raveling. I would never trust these welds structurally. Neither material is particularly amenable to welding, and you have no way of knowing if you have properly fused each cable wire or just made a stress raiser on it with the welding process.

 

[GregLocock]

That is completely unacceptable for any load carrying use whatsoever. That sort of termination, even if done well, probably has a UTS of about 3 of the strands (think about it). That level of workmanship probably isn't even that good.

This is one acceptable solution,

http://www.bosunsupplies.com/Machine-Swage-Fittings/

but you do need to get your wire lengths right. That is most easily done on site, you'd need someone who can operate one of these correctly

http://www.steelwirerope.com/WireRopeEquipment/OverviewSwagingMachines.html#.U6hwZI3F51M

which will not be cheap.

An alternative would be a thimble and then either a crimped swage or a couple of U bolts, aesthetically not a patch on the long ferrules.



Cheers

Greg Locock


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[JStephen]

I would guess that a significant part of the strength of the cable wires come from it being cold-drawn or something similar, where just heating it up to near melting and cooling back off probably vastly reduces the strength, regardless of how the details are worked.

 

[GregLocock]

Absolutely. Even cold working them to frizz them out for a termination is a bit of a no-no, heating them up to red heat is game over.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[SteelPE]

I sent the final report to the owner of the property saying that the existing system is not in compliance with the building code or accepted engineering practices. That is the end of my contract. I'm sure the installer is not going to be happy because this may hold up his final payment.

The systems I was looking at was produced by feeney and can be found at this link:

http://www.feeneyinc.com/Architectural/CableRail-Standard-Assemblies

there are plenty of others out there for purchase. I don't know why the installer didn't bother doing any research into the subject.

 

[jmen68]

I would bet that more than likely the contractor DID do the research and saw how much those connectors are! I priced some out for a buddy doing a renovation on his home. The fittings were the push in kind, where the cable would mechanically be bound as you pushed the cable into the fitting, I am not sure if that is how all of these systems work, but I digress. For ONE of these parts for a 3/16" steel cable was upwards of $35US. The contractor probably thought he could create an equal substitution for way less dollars than that.

 

[XR250]

The homeowner or contractor went the cheap route and did not use one of the available proprietary systems for cable rail.
You get what you pay for.