Strength of tieline?

[bobgaggle]

Someone wiser than me will chime in, I'm sure. But this seems more like a question of recognized acceptable/standard practice. That idea is tricky for me. Like you said, no entertainment rigger in their right mind would use single strand steel wire to hang a set piece. But drop ceilings are suspended with steel wire as standard practice. Different trade, different scenario, different standards.

 

[gafftaper]

Having a conversation with someone about the acceptability of using tie line or single-strand solid steel wire to rig Luan tree cut-outs with 1x3 spines (about 6' tall, 4' wide). My advice: don't do it, plain and simple. That I see shopping online, tie line does not have a clearly published safe working load or breaking strength. As discussed here, it's not approved or acceptable for overhead rigging. Single-strand solid steel wire, just like any kind of mono-filament, should not be used for overhead rigging either due to it's potential single point of failure and higher susceptibility to fatigue failure.

My question though, then, is how do we justify the use of tie line to rig curtains overhead? Or to secure cabling overhead? Obviously, part of the answer has to do with the distribution of a load. If a 200 pound curtain is hung from 50 tie lines all girth-hitched to the grommets, then each individual leg of tie line is only seeing a couple pounds of load. The same generally applies to securing cabling. Unless you are doing a single-pick to relieve stress on a big bundle of cable (which I wouldn't want to do with tie line), the loads involved are usually very distributed and therefore very small at any individual tie line. Someone could therefore make the argument that it is acceptable to use a piece of tie line to rig an object overhead that only weighs a few pounds (provided the knots/connections are appropriately made). I'm not saying that it's okay, I'm just saying someone could make the argument or assumption that it would be okay. At what load or under what conditions do we therefore consider it unacceptable to rely on tie line?

A few points:

- You would need to have dozens of lines fail at the same time for the curtain to fall.

-depending on the curtain the likelihood of injury due to it falling on someone is probably less than a hard object, even a fairly light weight hard object.

 

[gafftaper]

Also check out "Sein Twine" it's got a rated breaking strength. Line smaller than tie line is rated for hundreds of pounds.
Note:
-Having a rated material does not mean that you are instantly authorized to hang anything you want without proper rigging training.
-I doubt the manufacturer would approve it for overhead use.
-That's a breaking strength, not working load.
-Always use appropriate safety factors.
-Consult a rigger if you don't know what the points above mean.

 

[BillConnerFASTC]

Well - found "1/8" Kevlar Cord With Polyester Jacket Black" with a breaking strength of 825 pounds.

1/8 in. x 500 ft. Black Para Cord from the big orange box has a "working load limit" of 160. I'd guess breaking is 3 or 4 times that. 4 times is pretty common for many hardware items.

I know its way old post but let's be clear that some chain is "not approved for overhead lifting" . I suppose you could conclude that those that are not "not approved" are approved, but not really the case. Let's also clarify that "lifting" is absolutely different than dead hanging" and the basis for certain chains not being approved by the manufacturer for overhead lifting.

We hang (house) lights from their cord, and I'm not certain you can find a breaking strength for SO (and I doubt they are using the kind with a wire rope in it).

Necroposting.

 

[RonHebbard]

Having a conversation with someone about the acceptability of using tie line or single-strand solid steel wire to rig Luan tree cut-outs with 1x3 spines (about 6' tall, 4' wide). My advice: don't do it, plain and simple. That I see shopping online, tie line does not have a clearly published safe working load or breaking strength. As discussed here, it's not approved or acceptable for overhead rigging. Single-strand solid steel wire, just like any kind of mono-filament, should not be used for overhead rigging either due to it's potential single point of failure and higher susceptibility to fatigue failure.

My question though, then, is how do we justify the use of tie line to rig curtains overhead? Or to secure cabling overhead? Obviously, part of the answer has to do with the distribution of a load. If a 200 pound curtain is hung from 50 tie lines all girth-hitched to the grommets, then each individual leg of tie line is only seeing a couple pounds of load. The same generally applies to securing cabling. Unless you are doing a single-pick to relieve stress on a big bundle of cable (which I wouldn't want to do with tie line), the loads involved are usually very distributed and therefore very small at any individual tie line. Someone could therefore make the argument that it is acceptable to use a piece of tie line to rig an object overhead that only weighs a few pounds (provided the knots/connections are appropriately made). I'm not saying that it's okay, I'm just saying someone could make the argument or assumption that it would be okay. At what load or under what conditions do we therefore consider it unacceptable to rely on tie line?

@Smatticus I've posted this on Control Booth before but your post today is bringing back an educational memory.
In 1990 I found myself accepting the position of Head Electrician in a newly constructed theatre, brand new from the foundations up. In preparation I had purchased several spools of 3/4" black cotton flat twill tape and cut one spool into measured lengths of approximately 30" to have a decent stock of tie-line on hand to begin our first season's operation. The theatre's founders had begun decades prior in the Montreal / Ottawa area and had been in Hamilton for nearly 20 years but always renting performing spaces by the week, NEVER having owned, maintained or been responsible for their own building. The owners had opted to purchase all of their soft goods from a company in England and scheduled their delivery for their anticipated date of occupancy. You can imagine how that went, construction projects rarely are complete and certified for occupancy on schedule. Of course the British supplier shipped on time and the many heavy cardboard cartons sat on fork lift skids in the mud outside the theatre with the owners wrapping them in plastic as protection against the rain, sleet, snow and mud of our Canadian winter. As you can imagine, the heavy velour absorbed appreciable moisture and WEIGHT in spite of the several layers of thin poly / plastic.
FINALLY the official Certificate of Occupancy was awarded less than a week from the scheduled, and SOLD OUT, grand opening.
Tie line was provided by the fabricators for all of the borders, legs, sky cloth and both scrims but, due to their weight, the fabricators had recommended the purchase of chain to hang both black travellers and the extremely heavy and canvas lined House Curtain / Grand Drape, call it what you will.
CHAIN? Hell no said the carpenters, who'd never spent any appreciable time in a building with a fly tower and line-sets let alone a motor powered line-set.
Heck no.
It was decided hanging the house curtain should be the first order of business.
A forklift was required to elevate the damaged cartons one at a time on muddy skids up on to the truck dock.
On stage, the carpenters laid a layer of thin poly on the dirty stage then proceeded to lay their pristine velour face down on the deck with the burlap reinforced and grommetted edge down stage below the motorized line set #1 and the weighted lower edge up stage. The heavy curtain had been fabricated in two overlapping halves with both on-stage edges folded back and finished to allow for classy, paiged, centre bows. The carps had the first half unfurled and spread out flat and were forking in the second half when they realized they had the SL half on SR. The thin plastic they'd laid down was already ripped and in disarray when they commenced their kicking / shuffling walk attempting to move the SR half across to SL.
It didn't help at all that various contractors were still trying to traverse the stage with a variety of heavy steel road boxes and muddy wheelbarrows as they tried to vacate the site via the only truck dock.
Once the carp's had the velour positioned on the deck they elected to un-crate the curtain's heavy light-tight liner and position it face down on the velour.
Around about now they noticed the fabricators had failed to include ties for either the velour OR its canvas liner AND THEN they read the included notation suggesting the provision of chain.
CHAIN! Hell no!! We don't need no stinkin' chain! We'll just grab a few fist-fulls of Ronnie's pristine 3/4" flat cotton black twill tape. I tried to tell them, honest I did. I even tried to offer them a carton of jack-chain I had on hand from lowering fluorescent fixtures over several sewing machines up in wardrobe but HELL NO! We don't need no stinking chain. We're CARPENTERS and we KNOW what we're doing.
Their boss, the Head Carpenter, produced his key and lowered the electrically winched line-set in to it's preset lower end of travel limit. So far, so good. Then the Head Carpenter produced a second key and dispatched a carpenter minion to the grid to over-ride Hoffend's lower end of travel limit.
Now we're in scarier territory.
Knowing when I've met my match (along with being seriously outnumbered) I escaped to the relative safety of approximately the tenth row and got comfortable to watch the performance.
They lowered the powered line-set 'til it was practically on the deck; threaded one of my flat 3/4" cotton twill tapes through a grommet in the canvas liner, through another grommet in the heavy velour house curtain then tied the free ends together with various types of knots and hitches.
If you're paying close attention, you may have noticed no one had added anything to the bright yellow pipe-weights Hoffend had thoughtfully strapped to the single-purchase arbor.
Again, with the simultaneous use of two keys, they set the speed control at minimum and began to raise the line-set.
They cleared most of the other line-sets to the grid and began their process.
Motor up a little.
Stop.
Kick, kick. Shuffle, shuffle down stage 'til the powered line-set was close to vertical again.
Motor up a little.
Stop.
Kick, kick. Shuffle, shuffle down stage some more 'til the powered line-set was close to vertical again.
Repeat, repeat and repeat again until the curtain eventually cleared the floor.
I've mercifully skipped over the chaos that ensued when the motorized grooved head block lost its grip on the supporting cables where they contacted the head block for 90 degrees.
If / when you appreciate the cam-operated limit switch contained approximately 8 limits which had previously been carefully preset to slow the drive in four stages during its ascent and a similar four to slow it during its descent, you'll have a fore-shadowing of what's about to follow.
At some point it dawned on the carpenters that they might need to add counter-weights to the arbor.
Did they have any idea how many? HELL NO! But that wasn't going to stop them, remember, they're CARPENTERS.
Meanwhile I've lunched at the catering truck who was still visiting the site four times daily and was gleefully enjoying the matinee.
Finally, sometime prior to dinner, the carps thought they were done and, with the speed control still set at minimum, raised the curtain all the way to the grid, stopping it by releasing the up and over-ride buttons as there were no longer any meaningful limits.
Again, so far, so good.
Next they manually lowered the curtain in 'til it just touched the deck.
They boldly increased the speed just a little and flew the curtain all the way to the grid again.
Now, with their chests swollen with pride, they cranked the speed control to the max' and pummeled both the down and over-ride buttons withdrawing both fingers as the curtain neared the deck.
AND THEN IT HAPPENED.
Remember this was an SEW Euro-drive with no meaningful limits remaining, only the hard End Of Travel limits on the block wall behind the arbor.
When the Head Carpenter removed his two fingers from the two momentary buttons, the heavy and damp velour curtain jerked to a sudden halt then the over-stressed single wraps of twill tape snapped beginning with the extreme SR end rapidly continuing like a zipper faster and faster until all of the SR half of the velour and its canvas liner were in a damp mound on the deck whereupon the counter-weighted arbor SLAMMED into the bottom stop with this second sudden stop causing the entire SL half of the velour and its canvas lining to over-stress the remaining 3/4" flat cotton twill tape ties and suddenly descend to the deck ALL THE WAY from the grid.
The carp's presented one heck of a matinee. Their finale was stunning but they never came out for curtain calls.
When they rolled in the next morning I had all of the jack-chain I had in stock pre-cut and waiting for them, I even provided two pair of 10" Craftsman channel-locks as an additional courtesy.
I learned several lessons:
Gravity was still working and not to waste my breath attempting to educate carpenters.
Some things you can depend upon. @TimMc I'll bet you've got a few similar experiences to fall back on.
EDIT: To clarify; I'm MOST EMPHATICALLY NOT suggesting common plated #10 jack-chain is rated or recommended for overhead lifting applications but merely suggesting it is far superior to 3/4" flat cotton twill tape (and I won't even get into the non-cotton twill tapes)
Toodleoo!
Ron Hebbard

 

[gafftaper]

@BillConnerFASTC good idea with the Kevlar! Amazon has tons of options under "Kevlar cord" in different strengths and lengths. It's a bit pricey, but you could build a nice collection in 5', 10' 15' (or whatever custom length works well in your space) and reuse it a lot. That would be great to have around, and very strong!

 

[BillConnerFASTC]

My biggest concern with cords is knots and other terminations. I learned knots - at least most I need to know - when I as young and it seems as natural as walking - but I observe its not so natural for some. And knowing the knots and how much the affect strength is likewise important. Most knots reduce the strength from 20 to 40%. Whether or not you are comfortable that the 8:1 design factor accounts for that is another question.

 

[Smatticus]

@Smatticus I've posted this on Control Booth before but your post today is bringing back an educational memory.

That all sounds incredibly ridiculous and terrifying at the same time. @gafftaper That is a good point about the redundancy and multiple points of failure required for a curtain to come crashing down. Obviously, we just heard that is entirely possible if the ties are not properly chosen for the weight involved. Damp or not, I would not want any kind of curtain coming down on my head. Especially not one with chain or pipe in a bottom pocket. Fortunately many modern IFR curtains are much lighter weight than old Velour curtains of the same size.

@BillConnerFASTC I should have clarified, the scenery pieces in question are being suspended from a batten on a counterweight fly system... so not dead hung. It will be dynamically loaded as the batten moves. The particulars about what counts as overhead lifting can be confusing. JR Clancy's document about chain for theatrical use is helpful. From that document it sounds like "lifting" has more to do with a particular component moving across pulleys or around drums while suspending an overhead load than experiencing dynamic forces in general. Obviously even something dead-hung can encounter dynamic forces from wind or other objects pulling on it or colliding with it. As you pointed out, there is plenty of cordage out there that does come with a WLL, albeit often with an unknown maximum breaking strength. I have heard recommendations from riggers to de-rate the cordage or hardware to increase the margin of safety if you know the WLL but not the breaking strength or safety factor used.

Going back to our common tie line used for curtains and electrical cabling... if it doesn't have a WLL or breaking strength indicated on the product or packaging should we really be using it for any rigging purpose? I would say no unless you have actually carried out destructive testing to determine the breaking strength. Only then can you apply an appropriate safety factor and determine if it is suitable for the weight being suspended. You would also have to account for de-rating due to any knots tied as well. Such testing must have been done at some point, I would think by curtain manufacturers in particular, to determine the suitability for use. In Ron's story, the manufacturer clearly determined that those curtains had exceeded a weight acceptable for traditional ties and recommended chain instead. Such testing has likely been done by lighting manufacturers that are suspending fixtures from SO cord.

The difficulty of sufficiently carrying out such testing is another matter. Practically speaking, it makes more sense to start with a material that already has published data. As @gafftaper stated though, having a rated material is not license to rig anything. If you don't have an understanding of WLL, breaking strength, appropriate safety factor, appropriate attachment methods, etc you shouldn't be doing it. And yes, just because something has published data doesn't mean it should be used. There are a lot of other factors to consider such as quality of manufacturing, response to heat, moisture, fatigue, etc that play into whether something is safe for the application.

 

[BillConnerFASTC]

JR Clancy's document about chain for theatrical use is helpful. From that document it sounds like "lifting" has more to do with a particular component moving across pulleys or around drums while suspending an overhead load than experiencing dynamic forces in general.

I disagree with their conclusions. So does the committee that is responsible for the ASTM standard. The term comes from the ASTM standard. Nothing to do with it running over a wheel or rather there is 1 or multiple like on a batten. IIRC it was a chain sling failure lifted by a crane and cited by OSHA that resulted in this. And I agree - since a trim chain is overhead lifting, your tie line example would be too.

So, in my opinion, the Clancy paper is incorrect. It tries to spin a common practice to be permitted, when the chain manufacturers say it is not. I interviewed a lot of them - members of the ASTM committee. I do not believe the author of that paper did. So, even usual trusted sources can fall into that "if it's on the Internet..." trap.

 

[Smatticus]

I disagree with their conclusions. So does the committee that is responsible for the ASTM standard. The term comes from the ASTM standard. Nothing to do with it running over a wheel or rather there is 1 or multiple like on a batten. IIRC it was a chain sling failure lifted by a crane and cited by OSHA that resulted in this. And I agree - since a trim chain is overhead lifting, your tie line example would be too.

So, in my opinion, the Clancy paper is incorrect. It tries to spin a common practice to be permitted, when the chain manufacturers say it is not. I interviewed a lot of them - members of the ASTM committee. I do not believe the author of that paper did. So, even usual trusted sources can fall into that "if it's on the Internet..." trap.

Interesting and good to know. Is this the ASTM standard you are referring to? (ASTM A906/A906M - 02) What are your thoughts about this article from Entertainment Structures Group, which JR Clancy has also linked to on their website. More of the same? PS - Had to look up "IIRC," Urban dictionary says "If I recall correctly"

 

[BillConnerFASTC]

No. The one i was reffering to covers grade 30 and several other non-alloy grades, alloy being the key issue required by OSHA for overhead lifting. Very familiar with both documents you reference. I just don't believe you can redefine what the writers of a stabdard intended and confirmed. It would be like I tried yo redefine assemby occupancy as used by NFPA from more than 50 occupants to more than 30. Too bad the effort to dig in wasn't used to work with the ASTM committee to allow this application.

 

[Smatticus]

No. The one i was reffering to covers grade 30 and several other non-alloy grades, alloy being the key issue required by OSHA for overhead lifting. Very familiar with both documents you reference. I just don't believe you can redefine what the writers of a stabdard intended and confirmed. It would be like I tried yo redefine assemby occupancy as used by NFPA from more than 50 occupants to more than 30. Too bad the effort to dig in wasn't used to work with the ASTM committee to allow this application.

Okay, so we're talking about ASTM A413/A413M-07 which covers Grade 30, 43, and 70 for "purposes other than overhead lifting." It's interesting the ESG article mentions the A906 standard but not the A413. Is overhead lifting not defined in the A413 standard? The distinctions about "freely suspended" are interesting. Intuitively you would think of a fly system batten as being freely suspended... it's just not suspended from a single point. Though, you could think of a batten as being lifted from a single point because all the lift lines are anchored back to a single mechanism, whether that be the clew on an arbor or the drum on a hoist. Either way, a batten is 'suspended' and pretty 'free' to move in all directions. The definition in ASTM A906 does not make any distinctions about how many pick points there are, the method of lifting, or whether there is any counter-weighting balancing out the load. A flown batten is certainly in a position "that dropping the load would present a possibility of bodily injury or property damage." It seems that dead-hanging would not necessarily be counted as overhead lifting since the definition refers to "the process of lifting" (which I would read as actually moving a load)?

Independent of what the standards say, I do think it makes sense to analyze the characteristics of the chain and the application and be able to arrive at a conclusion regarding safety. If a proper engineering analysis of the application, in terms of material characteristics, dynamic loads, safety factors, etc shows that there is not a danger... perhaps the standards are too strict in their definitions or do not sufficiently consider this particular application? But from what you are saying, it sounds like there was not a sufficient effort by those in the entertainment industry to collaborate on the ASTM standard. Has this changed at all in the present day?

 

[BillConnerFASTC]

.. perhaps the standards are too strict in their definitions or do not sufficiently consider this particular application? But from what you are saying, it sounds like there was not a sufficient effort by those in the entertainment industry to collaborate on the ASTM standard. Has this changed at all in the present day?

I think that is accurate and I do not know if there has been any effort to modify the standard.

The manufacturers say don’t use their non-alloy chain for overhead lifting. OSHA says same. To try to redefine overhead lifting to seems exclude trim chains seems pointless to me. As to the committee intent, freely suspended means no other forces - like guy lines or wind - acting on it. So multiple lift lines is not the issue. Looking for rhetoric to change the the intent of the standard seems misguided.

 

[egilson1]

I think that is accurate and I do not know if there has been any effort to modify the standard.

The manufacturers say don’t use their non-alloy chain for overhead lifting. OSHA says same. To try to redefine overhead lifting to seems exclude trim chains seems pointless to me. As to the committee intent, freely suspended means no other forces - like guy lines or wind - acting on it. So multiple lift lines is not the issue. Looking for rhetoric to change the the intent of the standard seems misguided.

I would say things are not as cut and dry as Bill suggests. There are at least (3) interpitation memos from OSHA that address the question of non-alloy chain being used for slings. I’ve attached one that states that the use of non-alloy chain is not prohibited by OSHA, but that the use of any chain must be used in accordance with the manufactures recommendations. Turner & Seymour (aquired by peerless) aproved the use of 1/4” grade 30 proof coil chain for statically suspending (dead hanging) in a memo and defined “lifting” as the lengthening or shortening of of the chain itself. I also attached that.

I’ve been working with a few of the manufacturers to try and bring more clarity on this subject, but it has been a very slow process.

 

[BillConnerFASTC]

I've seen those before of course. I think there is more to the 1992 peerless letter. Also, I had that when I called and talked to their engineering folks at Peerless, and they backed off that view of overhead lifting. And the chair of the ASTM committee disagreed.

And be clear, grade 30 is not approved by any manufacturer for overhead lifting. I don't think OSHA lets you out of it.

Good luck convincing a jury that stage rigging is not overhead lifting.

No, the issue is not cut and dry. Its been clouded. But reach out to all the chain manufacturers as I did. I sent them photos and drawings of trim chains, and I found none stating it was an acceptable application for their grade 30.

Fortunately, Clancy and SECOA offered alloy alternatives. And there are now quite a few non-chain trimmimg devices or methods.

 

[kicknargel]

Going back to the tie line. . .

I was taught 8 lbs for tie line, but not sure that's backed up with science.

I also think there's some distinction to be made between soft and hard objects. A curtain falling on you would be no fun, but probably not life threatening. I suppose it could break your neck, but seems unlikely. Lauan and 1x3 could give you quite a concussion. This is also not backed up with science.

Standard practice must also come into play, in terms of data points. Are the any instances of curtains or cables causing injury by falling from failed tie line?

 

[danTt]

A curtain with bottom pipe falling on you is going to be a lot more than "no fun". I also think you introduce a bit of an interesting compound effect with curtains, where if the end tie breaks, your next tie is now holding more weight, and so on. Compounded with tielines that get fragile and easily breakable with age, and I could see room for some issues.

I recall at one point Production advantage attaching a number of ~100lbs to the tieline they sold. I can't remember if that was an MBS or a WLL number. Regardless, it does not seem to be on their website any more.

 

[lwinters630]

At what load or under what conditions do we therefore consider it unacceptable to rely on tie line?

I'm going with the word TIE. In other words if I'm using it to TIE some extra cable to neaten up a cable run on a batten. The failure of the line or knot would be non life threatening.
Or even hanging boarders or legs to battens every 12" OC. Again if one should fail, it would be non catastrophic.

When is it unacceptable?

When life or injury is dependent on it!

Then use rated cable and connectors.

 

[derekleffew]

...Or even hanging boarders or ...

Why you want to hang them? Did they not pay their rent?

How we gonna pay? How we gonna pay? How we gonna pay? Last year's rent?

 

[lwinters630]

Why you want to hang them? Did they not pay their rent?

Very funny LOL. And sometimes spellcheck is NOT my friend.