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View Full Version : Rigging Gear and Rust - When Does Cosmetic Become Structural ?



EddyCurr
01-07-2014, 08:21 PM
I have chain, wire rope slings and an old school manual block &
tackle type chain hoist that were gifted over the years. All have
rust. (I had never intended to use the B&T and have nearly scrapped
it on appearance because I own a nice large chain fall, however this
is somewhat out of reach at the moment and the B&T is at hand.)

Also, I see a 1T Wallace Tri-Adjustable Gantry crane that resembles
a VERY handy unit I used to have access to - until I discovered one
day that for inexplicable reasons some idiot cut it to pieces !?.

http://www.wallacecranes.com/triste1.htm

The Wallace comes with a trolly and what appears to be a very
substantial chain fall. However, all has been out in the weather
for an indeterminate time. Stenciled on the beam appears to
be a date of 1962.

What guidelines are there for evaluating whether such equipment
is safe at its rated capacity, ok to use at some de-rated value or
simply best to discard and replace?

.

demerrill
01-07-2014, 10:06 PM
Here's a couple of links that may give you a start:

http://www.anvilfire.com/health-safety/chain-hoist.php

http://www.hanford.gov/pageaction.cfm/search (search for 'rigging')

http://yabe.chudov.com/Army-Rigging-Handbook-FM-5-125/ebayhist.html

David Merrill

EddyCurr
01-07-2014, 11:50 PM
Thank you for the links. The AnvilFire link immediately offered up two rules
of thumb of particular interest for evaluating this equipment and several other
items for consideration. I will search the Hanford site and download the Army
rigging doc.

.

EddyCurr
01-08-2014, 01:06 AM
I see that gantry cranes fall under the auspices of crane inspectors.
For a fee, these organizations will examine and, if satisfied, recertify
a used crane. An engineer signs off on the certification.

While recert is probably prudent, if not mandatory for business use,
it might be a luxury for HSM. Certainly something to weigh while
considering used vs new.

.

J Tiers
01-08-2014, 08:37 AM
When you by new, you pay new price *including the cost of that same inspection*.

Of course, if there IS no such inspection "because it is new", then there are another set of problems....

vincemulhollon
01-08-2014, 08:56 AM
Something I don't like about the anvilfire link is he quotes uniform distributed loads for trusses and then claims 50% of the UDL is a good plan for a point load. You might want to look up some actual truss load limits because its not all that unusual for a CPL to be 1/2 of a UDL. So if you think you have a factor of safety of two because you derated by 50%, its probably no safety factor at all. Also he's assuming there is zero distributed load, which is highly unlikely during the winter. If you have a set of trusses derated to safely handle 5000 lbs UDL and 2500 lbs CPL that doesn't mean you can hang a 2500 lb load from the center at the same time as there's 1000 lbs of ice and snow. All the "junk" you hang in the rafters to distribute load across multiple trusses weighs a lot and has to be counted as a PL so even if your truss system could hold 2000 lbs with a factor of safety as a CPL, if you use 150 lbs of beams to distribute the load across multiple trusses and the "2000 pound" hoist and chains and lifting belts and stuff weighs 100 lbs you don't really have a 2000 pound capacity you have a 1750 lb capacity. If the roof collapses the insurance won't pay out if a structural engineer would have told you off, and builders being cheapskates you can bet it was built to the absolute minimum code required. Finally people who install stuff on trusses tend to do dumb things like drill holes thru the truss, so a 2x6 in a garage with a 3/4 hole thru it for a bolt isn't nearly as strong as a 2x6 without a thru-hole, it might be OK to put a load on it, but a lot of people put a load on it AND weaken it at the same time, which isn't going to turn out well.

My first fake job was an intern/gofer at a crane/hoist repair company and they had all kinds of (probably made up) stories about proof load lifts that didn't turn out very well. "So he used his service truck for a proof lift and the hoist drum brake broke, and that's why he doesn't work here anymore" or "... and then the roof buckled and filled the factory floor with snow and blocks of ice ... " that kind of story.

cameron
01-08-2014, 09:27 AM
I too don't like the cavalier suggestion to hang the load from the trusses , followed by a half-baked method of figuring how much load you can add. A lot of people, maybe even make that most people, don't have a really good understanding of how trusses work. Without that understanding, it would be wise to avoid adding any significant loads not considered in the truss design.

Most roof trusses are certainly not designed so that half the dead load can be slung from some random point on the lower chord.

EddyCurr
01-08-2014, 01:59 PM
As it happens, I am preparing an expedition onto my roof to clear snow
that both blocks vents and adds considerable load. Not from this year,
but the drywall across the ceiling shows evidence that accumulation in
the past must have been considerable.

No ceiling-mounted crane ways in my future. In fact, I am overdue for
a trip into the attic to investigate the state of the trusses, given the
signs apparent in the ceiling drywall.

While a free-standing bridge crane (with a long wide span so that the
supports were tucked up against the walls out of the way) would be
nice, I will wind up with something much MUCH less luxurious.

J Tiers, I can see now that the used Wallace gantry is fitted with a Yale
chain fall. Together, the new price must have been well more than ten
times the present ask.

The climate here isn't as severe on steel as in some places. Parts continue
to be available (and of course can be made, too.) Foreseeable lifting needs
come in well below the working capacity. I am well along in rationalization.

.

J Tiers
01-08-2014, 07:33 PM
Foreseeable lifting needs
come in well below the working capacity. I am well along in rationalization.

.

Hey, I have a half ton Yale differential hoist that has a stretched hook. I use it. I derated to 250lb, but it probably is still good to nearly the original load, or more, load rating, not ultimate.

The hook is opened by about a half inch, which had to be a severe overload....it's a chunky hook. The chain still looks OK, and there is no visible damage to the frame etc... and I have another one to compare to. Don't try that with the HF stuff.

When it's made right, it IS right.