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Messages 21 - 40 of total 67 in this topic << First  |  < Previous  |  Show All  |  Next >  |  Last >>
Tvash

climber
Seattle
Mar 25, 2015 - 04:53pm PT
So's yer I beam :)
Tvash

climber
Seattle
Mar 25, 2015 - 04:53pm PT
Angle isn't ideal for the app, as has been noted.
Tvash

climber
Seattle
Mar 25, 2015 - 05:06pm PT
Woops. I had you cantilevered out 4 ft, not 2'

a 4x4x5/8 structural steel angle will give you 7 to 1 under that loading if you attach the load and the angle correctly.

See what I mean about the drawing? :D

A ruler and pencil works for making straight lines.

Norwegian

Trad climber
dancin on the tip of god's middle finger
Mar 25, 2015 - 05:23pm PT
my favorite constant
is the radius of gyration.

Reilly

Mountain climber
The Other Monrovia- CA
Mar 25, 2015 - 05:30pm PT
Janis Joplin was the Queen of Gyration. Jess sayin'...
Steve Grossman

Trad climber
Seattle, WA
Mar 25, 2015 - 06:47pm PT
I rather like the obliquity of the ecliptic...
ionlyski

Trad climber
Kalispell, Montana
Mar 25, 2015 - 07:44pm PT
Hey this starting to get fun. Thanks for working with me here. OK here's some clarifications.

Tvash-correct, not cantilevered 4 feet out but more like 18" each side of the edge of the flange.
Also in reference to the 6X6 seeming huge:
So's yer I beam :)
Yes, but my load isn't

Banquo, cool links. I do have several beam clamps similar to those, I think both 2 and 4 ton. But I can't use those for this application. I have to create these points from the top of the beam, not the bottom and I need to create these two different rigid points. Similarly I don't see how any of those 4 point slings can help me out.

A couple more challenges are that I typically only have about 4 inches between the insulated ceiling and the top of the I-Beam. I am using Wilton super duty c-clamps for attachment, rated at 12,500 pounds each. These are small clamps with an opening size scaled to my needs for this application. The spindle of the clamp is hardened and 3/4" diameter. Due to the restriction above the I-beam, the clamps will need to be inverted. This is why I started looking at angle. I am aware of the twist potential of angle. My first choice was channel but the inverted c-clamp will not reach over the side legs of channel.

Can I reduce some of the twist potential by moving the holes for the forged eye bolts off center, towards the vertical leg of the angle?
TGT

Social climber
So Cal
Mar 25, 2015 - 07:59pm PT
Weld a tab to the vertical on the angle. Drill a hole in it.

use that for an attachment point.

Two angles back to back with four clamps and a tab in the middle?

Those Wilton clamps are bomber. Clamp as close to the vertical leg as possible.
Clint Cummins

Trad climber
SF Bay area, CA
Mar 25, 2015 - 08:25pm PT
Your drawing is very good.
It's good to dust off those old skills that you weren't sure still worked!

Can I reduce some of the twist potential by moving the holes for the forged eye bolts off center, towards the vertical leg of the angle?
I think you are moving towards the suggestion of Banquo and TGT - weld a second angle onto the back of the first to resist the twist.
This is like the channel you wanted, but clampable.
I think you want the clamp points to line up with the eye bolts which suspend the load.
All could be closer to the vertical part of the first angle, but if you don't have it backed by the second angle, if the load swings past the vertical it might load the clamps a lot?

Similarly, if you can't guarantee that you load and unload both eye bolts at the same time, you load one of the clamps with 750 pounds multiplied by some torque factor at 2'.
Banquo

climber
Amerricka
Mar 25, 2015 - 09:00pm PT
You want to apply any forces through the center of gravity of the section. For the 4x4x5/8 mentioned above, the cg is 1.23" from the two outside faces. For your sketch, you will want the bolt holes and the clamps 1.23" from the outside face of the vertical leg and 3.77" from the free edge of the horizontal leg.

To check the bending stress is a subject not generally covered until graduate school. Summarizing an old textbook:

1) Locate the centroid of the section (from tables 1.23")

2) Calculate the moments and products of inertia

3) Determine the directions of the principal axes and the principal moments of inertia. With equal legs this is probably at 45 degrees.

4) calculate the bending moments and stresses in the principal axes. You have to divide the moment up to match the principal axes and calculate the extreme fiber distances.

Since the top edge of the vertical leg is in compression and has no flange, better check buckling. There is a whole series of things to check in the AISC specifications for buckling. It would take me a day or so just to figure it out. Buckling is notoriously hard to predict.

Why not use a rectangular tube and have somebody weld flat plates to it for your clamps? Maybe a 4x4x1/4 tube with two 6x6x1/2 plates welded to it for the clamps. Go to 4 clamps. Have somebody check the welds and stresses. Nice easy undergrad analysis. Keep your factors of safety to 2 - 3 or 4 if people are at risk.
Tvash

climber
Seattle
Mar 25, 2015 - 09:31pm PT
yeah, 4x4x5/8 will do the job. i'd bolt it to the i beam tho 2" inboard of the flange edge. knock one of those wts horizontally and those clamps could slip

Z = M/max stress
M = 750x(18)
max stress = UTS strctl steel/7
solve for Z
pick angle size to match Z
locate mounting holes per post above

if u must use clamps, add 4 more on i beam as hard stops to prevent rotation of angle
Banquo

climber
Amerricka
Mar 26, 2015 - 07:45am PT
Be careful, somebody could get killed.

Angle bending and torsion spreadsheet. Believe me, this seemingly simple problem is very complex.
http://www.excelcalcs.com/repository/strength/beams/single-angle-bending-with-torsion/

Local buckling:
http://www.steel-insdag.org/TeachingMaterial/Chapter8.pdf

johntp

Trad climber
socal
Mar 26, 2015 - 07:52am PT
I still question why you need a separate angle rather than supporting the load off the wide flange
Tvash

climber
Seattle
Mar 26, 2015 - 07:57am PT
Cantilevered angles don't appreciate having their loads sway back and forth perpendicularly. Not great in torsion.

ionlyski

Trad climber
Kalispell, Montana
Mar 26, 2015 - 08:32am PT
JohntP-How can you achieve two different points three feet apart from one beam? Not in the direction of beam travel but in perpendicular fashion.

Arne
johntp

Trad climber
socal
Mar 26, 2015 - 09:07am PT
Arne- your sketch doesn't show the loads. How do you intend to connect to the loads? I don't really understand what you are doing, but why not just run a cable over the wide flange beam?
Clint Cummins

Trad climber
SF Bay area, CA
Mar 26, 2015 - 01:16pm PT
The loads are attached to forged eye bolts, which go in the holes that are 2" from each end of the angle piece.
750 pounds on each point.
(Just read Arne's first post in the thread).
ionlyski

Trad climber
Kalispell, Montana
Mar 26, 2015 - 01:43pm PT
Thanks Clint for the clarification.
Yeah and the credit for the sketch goes to my daughter. No way could I sketch that but she forgot to show the forged eyebolts.

My chain hoist hooks attach directly to the eyebolts. I'll say it again, I can't simply loop steel around the beam for this application. The distance between the points and their relationship need to stay fixed at those dimensions. That's why.

Arne
ionlyski

Trad climber
Kalispell, Montana
Mar 26, 2015 - 02:28pm PT
I like the idea of back to back angle. Could I not simply bolt them together? That way too, I'd have 4 Wilton clamps involved.

What would be the best way to create a single eyebolt point , presumably in-between the two angles?

Arne
Clint Cummins

Trad climber
SF Bay area, CA
Mar 26, 2015 - 02:56pm PT
Always great to get help from the kids!

Would a U-bolt that connects to both angles be strong enough?
It would get you the symmetry.

Maybe better is 2 eye bolts connected by chain?

Not sure if you need to connect your load directly to the backing angle, though.
It might be enough to just use the second angle to prevent twisting.
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