Home » Public Forums » GMCnet » Mech. Engineer Q.
| Mech. Engineer Q. [message #106472] |
Mon, 22 November 2010 17:09  |
g.winger
Messages: 792
Registered: February 2008
Location: Warrenton,Missouri
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I want to lift a load from a single point. The load is 8000 pounds. Not going to lift it very high and no one will be under it. The load will be supported on two points about 6 feet apart. How large of a I or H beam will be needed??? Can a smaller beam be used with a triangle brace on top help??? I'm an electrician,,, not an ME. Thanks,,,,PL
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| Re: [GMCnet] Mech. Engineer Q. [message #106480 is a reply to message #106472] |
Mon, 22 November 2010 19:11  |
Marsh Wilkes
Messages: 155
Registered: January 2004
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Hi Paul,
I am not a ME but if you just want to spread the cables to vertical, to
clear the load, a 4X4 will work as a spreader. The compressive load on the
4X4 would be dependant on how far above it the 2 cables came to a point,
naturally the farther above the spreader the lower the compressive load.
Just a SWAG would be about 12 feet. Here is a link to a calculator that will
figure the loads for you. I am sure someone hopefully a ME will give you a
more specific answer.
http://design.cablepick.com/rigging
Marsh Wilkes
Perry Fl
----- Original Message -----
From: "Paul Leavitt" <leavittpaul@yahoo.com>
To: <gmclist@temp.gmcnet.org>
Sent: Monday, November 22, 2010 6:09 PM
Subject: [GMCnet] Mech. Engineer Q.
>
>
> I want to lift a load from a single point. The load is 8000 pounds. Not
> going to lift it very high and no one will be under it. The load will be
> supported on two points about 6 feet apart. How large of a I or H beam
> will be needed??? Can a smaller beam be used with a triangle brace on top
> help??? I'm an electrician,,, not an ME. Thanks,,,,PL
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: Mech. Engineer Q. [message #106487 is a reply to message #106472] |
Mon, 22 November 2010 20:01 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
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| g.winger wrote on Mon, 22 November 2010 18:09 |
I want to lift a load from a single point. The load is 8000 pounds. Not going to lift it very high and no one will be under it. The load will be supported on two points about 6 feet apart. How large of a I or H beam will be needed??? Can a smaller beam be used with a triangle brace on top help??? I'm an electrician,,, not an ME. Thanks,,,,PL
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Paul,
From and engineering point of view there is some serious information missing here.
How can a single point be 6ft apart??
(I am going to assume [you know what that means] that you are lifting the load equally divided to the two points.)
How long is the beam you need to span the lift area?
When I have these answer I will go look for my steel book.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Mech. Engineer Q. [message #106506 is a reply to message #106472] |
Mon, 22 November 2010 22:39 |
Richard Denney
Messages: 920
Registered: April 2010
Karma: 9
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On Mon, Nov 22, 2010 at 6:09 PM, Paul Leavitt <leavittpaul@yahoo.com> wrote:
>
> I want to lift a load from a single point. The load is 8000 pounds. Not
> going to lift it very high and no one will be under it. The load will be
> supported on two points about 6 feet apart. How large of a I or H beam will
> be needed??? Can a smaller beam be used with a triangle brace on top help???
> I'm an electrician,,, not an ME. Thanks,,,,PL
>
I sort-of used to know how to do this stuff. If I were to tell a story of
how I might solve this myself, it might go like this:
According to my bazillion-year-old Steel Manual, beam loading pattern 7
(concentrated load at center of simple beam) has a maximum moment at the
loading point of Pl/4, where P is the load (in pounds), and l is the length
(six feet). So, 8000 pounds times six feet divided by 4 is 12,000 ft-pounds
of moment. The equivalent tabular load is 16,000 pounds, which is equivalent
to a continuous load of 2700 pounds/foot. An S3, which is the traditional
narrow-flange I-beam that one might use to support a trolley hook, in the
7.5 pound/foot weight has a depth of 3", a flange width of 2-1/2", and when
laterally supported will carry 5.2 kips/foot over a six-foot span. The
required lateral bracing is 10.1 feet, which is longer than your span, so
this can be considered laterally supported. That six-foot span will weigh 45
pounds.
Even a 3" C3 junior channel would be adequate for this load, providing a
maximum unbraced span of six feet and an allowable uniform load of 2.7
kips/foot, which is a total tabular load of 16,2 kips, which is greater than
the equivalent tabular load for an 8000-pound concentrated load.
I'm looking at plain, A36 cold-rolled steel, which has an allowable stress
of 36,000 psi.
The Steel Manual has many safety factors built in.
Though I claim no expertise and I have no idea what I'm doing, it seems
plausible. The bridge on my 20-ton press has two 4-inch channels of about
this weight with a span of two feet. Interpolating from the same table in
the steel manual reveals an allowable uniform load of 33 kips/foot. That
corresponds to a concentrated load of 66,000 pounds, or a little over 1.5
times the rated capacity of the press. That constitutes not too big a
ballpark to be within.
But if this is a gantry crane and the load will swing a lot, then you need
to factor the load up, particularly for its effect on lateral bracing.
Now, for the disclaimers. I am not an expert structural engineer and I have
not looked much in the Steel Manual since I bought the thing for college
classes about a zillion years ago. I make no claim to expertise, and I am no
providing engineering advice. I may have forgotten how to read this book.
I'm actually sort of surprised I even knew where it was. And, I am not YOUR
engineer. This is a paper exercise just for fun. If you intend to build
something that requires safety and an engineering analysis is required, you
must hire a local PE with structural expertise to do the analysis. If you
build it without that and it breaks and falls on your head, then that's the
price you pay for listening to a guy who happened to have a steel manual on
the shelf.
Rick "who knows nothing" Denney
--
'73 230 "Jaws"
Northern Virginia
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| Re: [GMCnet] Mech. Engineer Q. [message #106517 is a reply to message #106516] |
Tue, 23 November 2010 07:02 |
Ken Coit
Messages: 151
Registered: November 2005
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Are you designing a boat lift?
On Tue, Nov 23, 2010 at 7:43 AM, Matt Colie <mcolie@chartermi.net> wrote:
>
>
> g.winger wrote on Mon, 22 November 2010 21:10
> > The beam needs to be 6 feet long with 4000 pounds on each end. Supported
> in the moddle, 3 feet from each end. The load is above. Support under the
> beam. Kinda like a teter-toter. But it won't tip.
>
> So, What you are trying to lift is a single 8000# item with 2 lifting eyes
> 6' apart.
> You want to lift this item with a single point lift.
> Correct so far??
>
> How far is the hoist hook of the single point above the load eyes on the
> item ?
> If it is far enough for a lift bridle or a bridle and a spreader, we have a
> very simple solution here.
>
> Matt
>
> --
> Matt & Mary Colie
> '73 Glacier 23 Chaumiere (say show-me-air)
> SE Michigan - DTW 3.2/4R
> _______________________________________________
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--
Ken Coit, ND7N
Raleigh, NC
Parfait Royale
1978 Royale Rear Bath, 403, 3.07
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| Re: Mech. Engineer Q. [message #106519 is a reply to message #106472] |
Tue, 23 November 2010 08:10 |
g.winger
Messages: 792
Registered: February 2008
Location: Warrenton,Missouri
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Nope,,, A GMC support. Raise the rear a little high. Slide it under the pin boxes,,,,lower. Now you can adjust the front ride height without the stiff frame giving you an error. Just a thought. I have some scrap steel but its not heavy enough. Going to look at the mall. Was hopeing no one would think my idea was "silly",,,,PL (ya,,i know. Put the same amount of air in the bags or make them the same height. But what fun would that be???)
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| Re: [GMCnet] Mech. Engineer Q. [message #106523 is a reply to message #106519] |
Tue, 23 November 2010 08:40 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Paul,
IIRC Ken B and/or Ken H have a way to do adjust the front ride height that
accomplishes what you're trying to do.
Regards,
Rob M.
USAussie
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Paul Leavitt
Sent: Tuesday, November 23, 2010 8:10 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Mech. Engineer Q.
Nope,,, A GMC support. Raise the rear a little high. Slide it under the pin
boxes,,,,lower. Now you can adjust the front ride height without the stiff
frame giving you an error. Just a thought. I have some scrap steel but its
not heavy enough. Going to look at the mall. Was hopeing no one would think
my idea was "silly",,,,PL (ya,,i know. Put the same amount of air in the
bags or make them the same height. But what fun would that be???)
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Mech. Engineer Q. [message #106525 is a reply to message #106519] |
Tue, 23 November 2010 09:16 |
Richard Denney
Messages: 920
Registered: April 2010
Karma: 9
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Senior Member |
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On Tue, Nov 23, 2010 at 9:10 AM, Paul Leavitt <leavittpaul@yahoo.com> wrote:
>
> Nope,,, A GMC support. Raise the rear a little high. Slide it under the pin
> boxes,,,,lower. Now you can adjust the front ride height without the stiff
> frame giving you an error. Just a thought. I have some scrap steel but its
> not heavy enough. Going to look at the mall. Was hopeing no one would think
> my idea was "silly",,,,PL (ya,,i know. Put the same amount of air in the
> bags or make them the same height. But what fun would that be???)
>
>
This is rather interesting. A simple beam doesn't care if it's upside-down,
except for the effect of the weight of the beam itself, which in this case
is pretty negligible.
But I would suspect that stiffness is a more important parameter than
strength. I might be tempted to design for deflection rather than allowable
loads.
So, your concept of operation is to jack up the coach, slide the fixture
under the rear bogies, align hooks in the fixture to the openings in the
bogie frames (which would serve to prevent slippage and also to ensure
centering), and lower the coach onto the fixture. The fixture would include
a rocking foot in the middle of the beam. An out-of-balance coach would
settle to one side, so it would need to be low to the ground. You might be
able to make it low enough so that it will slip under the bogie frames with
the bags full, so that all you have to do is empty the bags after sliding
the fixture in place. The tires would still contact the ground, but I don't
see that as a problem. The fixture would hold the rear at proper ride
height, at least when the coach is balanced on it, which it will be after
adjusting the torsion bars to provide the correct front ride height. When
the front ride height is correct and the fixture is balanced (equal gap to
the ground on both sides), air the bags back up, remove the fixture, and
then adjust the rear levelers to achieve proper rear ride height. That
process could be pretty simple for anyone to do. I'd be interested.
I was thinking the center pivot needs to be high, but I'm thinking better of
that. If it's lower, the coach will lean more easily, but as long as the
ground clearance of the fixture is relatively low, one end will rest on the
ground before the coach leans very much. A pivoting foot welded to the
center of the beam on the underside of the bottom flange might work.
You might consider back-to-back channels. Then, you could fabricate end
hooks and the center pivot from plate stock, and sandwich it between the
webs of the channels. If the rests on the ends were 1/2" plate, the center
foot could be 3/8" plate, which would give it room to rotate freely.
Rick "liking it" Denney
--
'73 230 "Jaws"
Northern Virginia
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| Re: [GMCnet] Mech. Engineer Q. [message #106529 is a reply to message #106525] |
Tue, 23 November 2010 09:56 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Rick,
I raise the rear end of The Blue Streak Downunder with a 20 ton air over
hydraulic bottle jack on the 2" thick walled bumper hitch. Ya reckon this
will accomplish the same thing Paul wants to do with his fixture or is it
important to support the GMC in the center of the rear wheels? I'm not
willing to spend the biccies (money) to buy an air over hydraulic jack for
Double Trouble but I could use a hand pumped one.
Also I don't understand how this will work.
"The fixture would hold the rear at proper ride height, at least when the
coach is balanced on it, which it will be after adjusting the torsion bars
to provide the correct front ride height."
Could you please explain it a bit more.
Thanks,
Rob M.
USAussie
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Richard Denney
Sent: Tuesday, November 23, 2010 9:17 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Mech. Engineer Q.
This is rather interesting. A simple beam doesn't care if it's upside-down,
except for the effect of the weight of the beam itself, which in this case
is pretty negligible.
But I would suspect that stiffness is a more important parameter than
strength. I might be tempted to design for deflection rather than allowable
loads.
So, your concept of operation is to jack up the coach, slide the fixture
under the rear bogies, align hooks in the fixture to the openings in the
bogie frames (which would serve to prevent slippage and also to ensure
centering), and lower the coach onto the fixture. The fixture would include
a rocking foot in the middle of the beam. An out-of-balance coach would
settle to one side, so it would need to be low to the ground. You might be
able to make it low enough so that it will slip under the bogie frames with
the bags full, so that all you have to do is empty the bags after sliding
the fixture in place. The tires would still contact the ground, but I don't
see that as a problem. The fixture would hold the rear at proper ride
height, at least when the coach is balanced on it, which it will be after
adjusting the torsion bars to provide the correct front ride height. When
the front ride height is correct and the fixture is balanced (equal gap to
the ground on both sides), air the bags back up, remove the fixture, and
then adjust the rear levelers to achieve proper rear ride height. That
process could be pretty simple for anyone to do. I'd be interested.
I was thinking the center pivot needs to be high, but I'm thinking better of
that. If it's lower, the coach will lean more easily, but as long as the
ground clearance of the fixture is relatively low, one end will rest on the
ground before the coach leans very much. A pivoting foot welded to the
center of the beam on the underside of the bottom flange might work.
You might consider back-to-back channels. Then, you could fabricate end
hooks and the center pivot from plate stock, and sandwich it between the
webs of the channels. If the rests on the ends were 1/2" plate, the center
foot could be 3/8" plate, which would give it room to rotate freely.
Rick "liking it" Denney
--
'73 230 "Jaws"
Northern Virginia
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: Mech. Engineer Q. [message #106530 is a reply to message #106472] |
Tue, 23 November 2010 10:31 |
rwbmitiopt@comcast.net
Messages: 189
Registered: April 2005
Karma: 0
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Senior Member |
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Look up "flitch beam". Great solution for a header when perserving head room is critical.
Randall
| g.winger wrote on Mon, 22 November 2010 15:09 |
I want to lift a load from a single point. The load is 8000 pounds. Not going to lift it very high and no one will be under it. The load will be supported on two points about 6 feet apart. How large of a I or H beam will be needed??? Can a smaller beam be used with a triangle brace on top help??? I'm an electrician,,, not an ME. Thanks,,,,PL
|
Randall Burns
Sammamish WA
75 EX GB
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| Re: [GMCnet] Mech. Engineer Q. [message #106537 is a reply to message #106530] |
Tue, 23 November 2010 11:26 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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From all of this conflicting information, it sounds like someone is trying
to lift the rear of a GMC coach high enough to have the rear tires clear the
ground, and then support it under the bogie boxes. Presumably it would be
lifted by a floor jack under the center of the coach and then jackstanded
under the lifting beam with the two supports approx 6' apart outward 3' each
from the center or lifting point. I assume that all this is to allow the
front ride height to be adjusted without the influence of the rear
suspension to affect adjustment. Just a guess on my part, but wouldn't frame
jackstands accomplish the same thing?
Jim Hupy
Salem, OR
78 Royale 403
On Tue, Nov 23, 2010 at 8:31 AM, rwbmitiopt <rwbmitiopt@comcast.net> wrote:
>
>
> Look up "flitch beam". Great solution for a header when perserving head
> room is critical.
> Randall
> g.winger wrote on Mon, 22 November 2010 15:09
> > I want to lift a load from a single point. The load is 8000 pounds. Not
> going to lift it very high and no one will be under it. The load will be
> supported on two points about 6 feet apart. How large of a I or H beam will
> be needed??? Can a smaller beam be used with a triangle brace on top help???
> I'm an electrician,,, not an ME. Thanks,,,,PL
>
>
> --
> Randy Burns
> Sammamish WA
> 75 EX GB
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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