Reply to post by Scott, on December 24, 1999 at 00:38:54:

This is precisely where the complexity builds. Calculating the stresses of shock loading is not easy, especially without a system of measuring to test assumptions (my reasearch funding is rather limited [g]). The past few months I've spent a little time learning some analysis software, but it's slow going due to time limitations.

Calculating the forces of a falling limb are is even more difficult. That will depend heavily (pun intended) on how the limb breaks, and the various angles at time of failure.

Failure of a cable is most likely under shock loading. The integrity of the cable and hardware is crucial- even minor defects can be amplified and the capacity exceeded far below expected ratings when there is worn hardware or improper installation.

Reply to post by Scott, on December 22, 1999 at 20:41:09:

It is still unclear to me how the calculated weight of the supported limb is referenced to the cable size/strength. I have seen the size/strength table for common and EHS cable. But I hear that the full weight of the limb is not to be supported, only the failure-force-moment at the point of attachment. So how is the weight-of-limb calculation actually used to determine minimum cable strength for the application? Where should I look for standards/rules of thumb.
One more question: does the Chicago cable grip work equally well on both types of cable? Or is it necessary to have a different type of grip for each cable type (common/EHS)?

Reply to post by Mark Goodwin, on December 23, 1999 at 07:17:47:

Mark, I never got clear on day to day application of the strenght tables to calculated weight! That's the point I was trying to make in this thread.... I don't think it's practical to do the actual calculations, there are too many unknowns.

Looking at the OLD NAA tables, they seem very consertvative going by limb diameter. 15" being maximum size for 5/16 common cable, 18" max for 3/8 and anything above 20" to use 1/2. I've never even seen 1/2" 7 strand common cable stocked anywhere, let alone used it.

The interesting thing is the table specifes "load in pounds" not "weight." I think "load" has more to do with branch length and angle and with exposure to loading forces (like wind) than weight.

So that puts you back to judgment and experience. I'm sorry I can't refer you to more useful rules of thumb. Anybody else out there?

GRIPS. My understanding (a little dated) was that pre-formed grips were for EHS cable only and that common cable needs to be hand spliced. All that's needed is a pair of linesman's pliers and it's not hard to do. Not hard to do well with a little practice. If you can't find a graphic, maybe Russ can scan one in. I can't seem to find one handy. I've heard some companies say it's much easier to train field people and maintain quality with pre-forms, and I've heard other companies say the exact (well almost) opposite.... pre-forms might be easier for the minimally trained person to put in right but also easier to put in wrong... with good training hand splicing is better. There are BIG companies that still exclusively use hand splicing. Pre-forms were just coming into use when I got out of the installation end of the business, I only used them myself a few times, so I really can't offer any extensive comparative experience.

Maybe Santa left a pair of Klien linesman's pliers under your tree! Have a happy.

Reply to post by Russ Carlson, on December 24, 1999 at 06:16:44:

10-4. Understanding the calculations is good background. Certainly good to know if you find yourself in the consulting and educating end of the industry.

But for practical purposes CAREFUL AND PROPER HARDWARE SELECTION AND INSTALLATION ARE MUCH MORE IMPORTANT!

I've never seen a properly sized (I know Mark.. where are the guidelines?) cable break unless it was old and rusted, or nicked in installation or improperly spliced or gripped. I've seen nuts back off sloppy bolt installations (yes Tom!), I've seen bolts bend and ultimately snap if the cable pulls off line, I've seen only one drop-forged bolt installed in line snap... it was shortly after installation and I can only assume it was defective or damaged, I've seen lags pull out of decayed wood or the wrong (oversized) hole.

They were having snow last night in Rome, so I guess that means Syracuse too . But I'me sure you have the snow tires on for tomorow's drive!

Reply to post by Scott, on December 25, 1999 at 00:41:51:

Blair shows two types of cable grips (grabbers, not TreeGrips)for holding the cable end prior to splicing, etc. The Havens is shown on common cable, and the Chicago is said to be designed specifically for EHS cable. I was wondering if the Chicago grip could also be used on soft cable, or if each of the two types should be used only with one type of cable. It says the Chicago has 4 inch long parallel jaws that do not kink or cut into the coating of EHS cable (to prevent rust). If I thought I would be using EHS sometimes, and the one "grabber" could hold both cable types, I wouldn't buy the Havens. But if I thought most of my cabling would use common cable, and Havens held that kind better, I would get it instead, at least to start. Thanks for all the replies.

Reply to post by Mark Goodwin, on December 25, 1999 at 06:26:18:

Sorry Mark I misunderstood, I thought you were referring to the "grips" used to attach cable to hardware. I can't give you an answer on the cable clamping 'grips,' I just don't know.

You do need to be careful... I picked up an old grip intended for tensioning fence wire in a flea market once and quickly learned in had sharpish gripping edges which would nick the soft cable.

Reply to post by Mark Goodwin, on December 25, 1999 at 06:26:18:

Mar, I have not actually used the Chicago grip. However, it is my understanding that it can be used on both EHS and soft (malleable) cable. The Havens grip pinches with a curved cam, so that can crimp the cable a bit. The flat matching plates on the Chicago grip will hold the cable without crimping. I would think it would be fine to use on the soft cable.

Reply to post by Scott Cullen, on December 16, 1999 at 22:23:11:

Scott, failure of a member sideways to the cable does not seem unlikely to me. Sometimes we wish we could triangulate, but cannot. Due to there only being 2 members to use as (anchor and anchored.)

Reply to post by Peter Torres, on December 17, 1999 at 07:43:25:

If there is a recognizable possibility of this type of failure, you either need to install bolts at the crotch, or consider the more drastic measures (removal of the weak limb).

Reply to post by Scott Cullen, on December 16, 1999 at 22:23:11:

Thanks, Peter and Russ, for the responses. But I need to repeat my question. "What factors or characteristics would you use to identify a system subject to failure in a sideways vector.... i.e. not perpendicular to the crotch? Are there factors other than decay?"

If we use terms like "not unlikely" do we need to use it in some context of frequency or liklihood? My personal recollection is that most failures seem to be of crotches with included bark and the failure is perpendicular to the line of bark, i.e. parallell to where a cable would have been installed. Most failures not in this vector seem to be branch fractures unassociated with a crotch.... decay or other defect, SLD, catastophic "twisting" failure as seen with tornado like winds or micro-bursts... and cables would probably not even have been indicated in these situations.

I can visualise situations where a limb defect might be cabled... because it has a small defect or the system is engineered to hold the limb in the tree even if it does fail, so the target is protected.

What characteristics or sets of characteristics do you look for as indications of potential failure "sideways to a crotch?"

Reply to post by Scott, on December 17, 1999 at 07:43:25:

When I see limbs that have uneven weight distribution I might think of installing a side cable. Lions's tailing comes to mind, both natural and chainsaw created. I also look at the direction the limb is growing. If we have normal winds, they are from the north and northwest in the winter and northwest to south in the summer. That is a small consideration in my plan.

There may be a defect on one side of a limb. Sometimes limbs have a spiraling crack that needs support.

You are right in your assesment of failures. When the limbs fail sideways it is generally the result of some heavy weather.

Side cables may be called for when the inline cable might allow too much movement and strain the branch union.

Reply to post by Tom Dunlap, on December 29, 1999 at 06:55:37:

OK, it sounds like you're decribing two main sets of characteristics that might indicate a potential for failure sideways to the crotch.

ONE is a defect in the body of the limb itself... decay, a crack, a top heavy or "lion's tailed" or poorly tapered limb. These failures would be fractures or splits completely unrelated to the crotch... so orientation to the crotch is not a factor... the failure will be oriented with the defect and loading.

TWO is a crotch or branch union failure. I can see that a limb which has decay at the crotch or which grows at an angle that is not perpendicular to the crotch might have a higher liklihood of sideways failure than a more typical crotch.

So the questions remain. In either type of situation will cabling reduce the risk and what else might be done? As Russ points out, bracing rods are sometimes indicated to stabilize either branch or crotch cracks. "Side" cables may be indicated, but I'd guess that suitable "side" anchor points are not frequently available. (I'm assuming here that by "side" cable you mean an additional cable to a single limb and not a typical "double" or "triangle" cable pattern that ties in multiple limbs with a shared crotch or with crotches perpendicular to each of the cables.) Decay presents another a big variable.

So, back to your very first question.... beyond very general parameters are there guidelines or is it really a matter of judgment and experience?

Reply to post by Russ Carlson, on December 20, 1999 at 23:40:16:

Any idea how do these figures change when a tree dies, but remains standing? Such a tree is no longer "green", but is just as full (if not more so) of water.

Reply to post by Ed Milhous, on December 21, 1999 at 01:42:24:

Generally the wood tends to dry out over time, once the tree dies. A live tree transports water internally, maintaining a moisture content higher than dead wood. Once dead, the wood slowly loses the moisture internally, since it cannot be replenished. Water from the atmosphere, either from humidity or precipitation, does not readily penetrate the wood tissues, especially when the bark remains intact. There is some a lot of variation, and the moisture content of standing dead wood will depend on all the various factors- wood density (species) season, ambient moisture conditions, etc.

I do not have any figures for weights of standing dead wood that I can find. Dead wood will seldom weigh more than live wood, so by using green weight figures, I would think you'd probably be on the conservative side.

Reply to post by Tom Dunlap, on December 10, 1999 at 18:15:58:

Browsing through older thread I found quite an extensive one on this topic. I read a few and there are some sound observations there too.

Link below.

Reply to post by Scott, on December 10, 1999 at 18:15:58:

Won't accpet the URL, you'll have to type it in yourselves, sorry.

http://tree-tech.com/board/?topic=topic2&msg=384

Reply to post by Scott, on January 04, 2000 at 07:08:23:

To add a link to a URL, you must enter both the "Link URL" and the "Link Title" when posting a followup. The first, Link URL, is the web address (http://www.etc,etc,etc.com). The second, Link Title, is any descriptive title you wish to give the link. The title shows up with your posted message, the Link URL directs your browser to the site, but remains hidden.

Both are necessary for the link to work.

Reply to post by Mark Goodwin, on December 17, 1999 at 07:43:25:

Does anyone know of compression-type clamps being used to secure cables in trees?
I'm thinking of the kind of clamp that is squeezed onto the cables (permanent attachment).
This was suggested to me by someone recently, and I have not seen it referred to in the literature on tree cabling and bracing.

Reply to post by Mark Goodwin, on December 17, 1999 at 12:21:45:

I think that you are thinking of swaging. Aircraft style cable is used and the splice is made with a soft metal sleeve that encompasses both ends and then is crimped. This is standard for some marine applications but for some reason it has not been used in trees. A while ago I did a little research into swaging for trees and could find no reason to not use it. One part to consider is the shock loading or karate effect on the swage. Also, what happens if the cables start to rust? They will get weaker.

As far as strength goes, the system can be sized to take the same loads that EHS is expected to take. 3/8" 7x19 stainless steel wire or 5/16 1x19 galvanized steel wire is rated for a load of about 12,000 pounds. These figures are taken from Brion Toss' book "The Complete Riggers Apprentice". He has tables to figure out the stretch of the cable too.Go to a bookstore and read the section on wire rigging, pages 145+. Swaging requires more skill than using tree grips but the skill can be monitored and taught.

Tom

Reply to post by Mark Goodwin, on December 17, 1999 at 12:21:45:

I think the type of connection Tom describes is trademarked "nicopress," but there may well be generic forms available. The crimper looks like a giant version of the one you might use to crimp electrical connections. I have seen them routinely used in guying newly planted trees. They install very quickly, particularly when you need to do three guys, maybe with turnbuckles. The installation is visually clean and not subject to tampering like the u-bolt and nut type cable clamps. But speed is the biggest advantage. We used them in that application but never up in the tree. I'd guess improperly done they can slip, so training is important.

I'm not sure then same time advantage is as important up in the tree. Considering the set up time to get in place and ready for splicing in the tree the %age saving per cable end might be pretty small. But the %age saving per small tree guy wire might be significant.

First time I ever saw them was to splice the cable to the hook on mechanical come-a-longs. So they hold up under pretty heavy and dynamic loads. That's what got us looking into them. You may also see them on garage door cables and the cable actuated lifts in automotive service shops.

Reply to post by Tom Dunlap, on January 06, 2000 at 15:19:01:

Tom, I can't seem to find any reference sources right now. Does swaging refer to any sort of deforming of a metal fixture? For some reason I thought of crimping as a squeezing or compressing action and swaging as more of an expansion into a confined space.... like putting a wedge into an axe handle so it expands inside the head. I'm picturing cable connectors that bring the cable into the bottom of a cone shaped collar and then spread the cable strands inside the cone with introduced material. Similar treatment of rod ends. But I can't find any actual pictures or diagrams at the moment.