Cable Clamps 3

[BSVBD]

We're installing a door in an existing PEMB where there is cable-brace.

I need to cut and relocate the cable and reclamp to a fabricated bracket, then anchor it to either the existing concrete slab or foundation wall, if possible.

Any good references for cable clamps with allowable load charts/values? Currently I'm checking into Granger and McMaster-Carr.

Any other recommendations when dealing with cable clamps and clamping?

 

[BSVBD]

My research shows that McMaster-Carr offers a Wire Rope Compression Sleeve, stating, "For 100% of the Ropes Capacity". (When used with the appropriate compression tool)

I have no reason NOT to trust this other than i've never specified these before.

Any words of wisdom on this?

Thank you!

 

[jayrod12]

Crosby is the go to supplier around here for everything cable related.

 

[BUGGAR]

Under cyclical forces, cable braces can go slack before the next cycle. Make sure the clamp can undergo a reversed force without losing grip.

 

[Lomarandil]

I'm having a tough time visualizing what you are trying to do (not your fault, just different industry than I work with).

Crosby wire rope clips are definitely an easy, affordable way to splice two parts of wire rope. You will take a hit in capacity though, either 10% or 20% depending on the cable size.

 

[SlideRuleEra]

Agree with Jayrod12 about the Crosby brand being common. In the heavy construction business all cable clamps are often called "Crosby Clips".

A properly prepared wire rope termination, with clamps correctly installed has an assumed efficiency of 80% (of the wire rope's breaking strength) for smaller diameters and 90% for larger diameters. See the manufacture's specific recommendations at Crosby Clips - Warnings & Application Instructions

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[BSVBD]

SlideRule,

I noticed the 80 & 90% efficiency through my research of Crosby Clips. Thank you, however, for the concerned warning!

However, I'm favoring the McMaster-Carr Compression Sleeve which, as published, provides "...100% of the Ropes Capacity"

What i found interesting is that, for this specific project, the original metal building wire-rope termination is the typical loop through the eye-bolt, back and then braided to itself.

 

[andriver]

2nd Jayrod, Crosby is the place to go

 

[Lomarandil]

BSVBD -- nothing too unusual about that (except perhaps the application) -- just a hand-tucked splice.

 

[jayrod12]

The 80-90% efficiency is against the breaking strength. Then you go and apply a large safety factor to get the working strength of the cable. There's likely an engineer or two that would neglect the capacity loss from the clips when comparing demand to the working capacity.

 

[SlideRuleEra]

BSVBD - You are welcome. Swaged (compression) fittings are very efficient, near 100%, but before taking McMaster Carr's "word" at face value, at least read the Crosby Wire Rope End Terminations User's Manual

See page 8:

The Working Load Limit rating of the termination/wire rope combination is not entirely a function of the fitting being used. Therefore, the listing of the working load ratings is not within the scope of this literature. (Refer to the Wire Rope Technical Board’s “Wire Rope Sling Users Manual” for these values).

On the same page:

It is important that the proper components be used to make a termination. For a specific style wire rope termination, you must choose the correct size and type of fitting and its corresponding swaging die.

Are the detail specs for the existing cable known?

Beginning on page 10, look at the sizeable shop presses needed to get high efficiency terminations. Will a portable field press be use on the existing cable?

As a former bridge contractor I had a lot of swaged slings professionally shop made and even personally made a few with Crosby Clips. If the work is performed in the field, probably very good, but not 100% efficient.

Jayrod12 - Not recommended by Crosby, see page 6.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[jayrod12]

Of course it isn't recommended by Crosby. But keep in mind that the general accepted safety factor is 5 on the breaking strength however no where is that a hard and fast rule and in fact most of the documentation I've seen says it depends heavily on the intended use and can range between 3-7. Therefore if I typically use a safety factor of 5, and need to use 85% of the working strength, I'm not increasing the diameter. If I'm flirting with 100% of the working strength, then I'm going up a diameter.

Some things are discretionary.

 

[SlideRuleEra]

Jayrod12 - Ouch. For the OP's application, which is what is important on this thread, I won't quibble with you. Reducing the safety factor a little is not a big deal. But what needs to be pointed out that is not always the case, the OP did state he is new to wire rope terminations.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[jayrod12]

Apologies if I came across harsh. That was not my intent. I was merely pointing out another view on the entire design process. Safety factor choice is just as important as proper termination details.

 

[BSVBD]

jayrod, i don't perceive any harshness in any of your replies... cautions, warnings and advice is likely the most profitable and life-saving input within this site.

jayrod and sliderule, it appears as though Examples #1 & #2 on page 6 of Crosby's Users Manual DOES recommend a 5:1 safety factor. What am i misunderstanding when you both say "not recommended" by Crosby?

It seems in order to determine an acceptable termination or quantity of terminators, whether compression sleeves or wire rope clips, i need to work the numbers in reverse or basically use 5x / 0.8 efficiency or 6.25x the number of sleeves or clips assuming the original metal building designer used near 100% of the wire rope allowable WLL. Did this make sense? In either case, the resulting quantity seems unreasonable.

Would the metal building designer have designed the wire rope to resist up to breaking strength or WLL?

I DO realize, that we have no idea what tension load the wire rope was designed to resist, without making assumptions.

Any other suggestions?

Thank you!

 

[jayrod12]

The metal building designer should have designed to the WLL of the wire rope. It's likely that they are near 100% of it based on any of my other experience with metal buildings.

The most commonly accepted safety factor is 5 for wire rope. What SRE and I were debating is the efficiency reduction of the end termination detail. If wire clips are used you are required to reduce your breaking strength (and therefore your WLL) by 20% or so. Other end termination details allow up to 100% efficiency. What is possibly up for debate (depending on the situation) is an acceptable safety factor (which may be more or less than 5 depending on the situation)

According to the Crosby catalogue on page 117 I think there is the number of clips required based on the cable diameter.

Can you give a quick analysis of the building to take an educated stab at the load in the cable?

 

[SlideRuleEra]

Agree with Jayrod12.

Many of the Crosby recommendations are conservative, assuming that their products are used for hoisting loads (with the risk of crane operator error, impact loading, life-safety for workers, disastrous consequences of a falling load, etc.).

On my website you can download the "US Steel Wire Rope Engineering Handbook". Page 6 of this book lists US Steel's thoughts on "minimum safety factors" for various applications... they range from 3.2 to 8.0.

Cable clips don't have an absolute load rating for each clip. If, say 4 clips are rated 80%, using a fifth clip will give only a slight increase in efficiency (maybe to 85%... probably less).

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[dhengr]

BSVBD:
Wire rope in that bracing application in a PEMB seems kinda weird to me. Wire rope stretches quite a bit as it is brought up to load, so bldg. drift could be quite high. Likely not a good thing. There is both elastic stretching (material/wire strain) and mechanical stretch, the tightening of the wires which make up the cable strands as they compress and tighten in the strand. As I recall the 5:1 (breaking strength/working strength) ratio commonly cited for wire rope primarily applies to its abusive use in load lifting rigging and boom and hoist rigging for cranes and the like. Then, today, the finished product is load tested to 1.25 its rated cap’y. before it can be used. It seems to me that I have seen FoS of 2 and 3 (vs. breaking strength) for wire rope use in more static, less abusive structural applications. I would be more inclined to use steel rods for this type of bracing, with welded end fittings, which are then pinned or bolted to the structure and a turnbuckle in the middle for tightening. They are easier to fab. and handle and have a smaller and more controlled elongation under load.

I doubt very much that you are going to be doing any real heavy duty field swagging of end fittings. You really need heavy presses to do this in a controlled shop environment, for any quality control. You will need to know the exact length of the cable needed, or provide some length adjusting feature.

 

[SteelSlugged]

I agree with dhengr. General purpose wire ropes have a lot of stretch. You won't get near E=29,000ksi, so your deflections with rope will be higher.

Also, the IBC and ASCE prohibit the use of clamps for cables resisting lateral loads or really any structural loads, depending on how you interpret it. For a building covered by one of these codes, you must use an end termination that does not reduce the capacity of the rope itself. You are then limited to swage fittings, like dhengr mentioned, or spelter sockets. Spelter sockets do not require special equipment, if you specify a thermo-set resin to lock the cable into the end fitting.

Crosby will not recommend using wire rope clamps for permanent loads. The clamps relax over time, even under static conditions (wind loads aren't truly static). They require periodic inspection and retightening of the clamps. Also, wire rope clamps are known to fail spectacularly when hit. Rods or ropes with more structurally sound end connections are more robust.

Depending on your loads and safety factors, you can use your own judgment whether or not wire ropes are suitable, but check with the AHJ, because the IBC and ASCE don't seem to allow them.

 

[Ussuri]

Spelter sockets have an efficiency of 100%

Link