Beam design and deflection
Beam design and deflection
(OP)
I need to fabricate a small beam to lift a load with center point loading.
A channel shape works best for the beam design due to space constraints. In my situation, I would utilize a channel shape with the 'C' pointing to the ground, lift at the center bottom to lift a equal load on each end at the top.
Looking at moment of inertia and weight per foot, I would be much better off using 2 unequal leg steel angle iron sections to form a channel shape versus using a common steel channel. Obviously the longer legs would be in the vertical direction to increase strength.
My question is how to weld the channels, and would this arrangement result in strength comparable to the sum of the moments of inertia of the two angles? I believe welding a 1" deep weld each foot length along the entire length of the angle iron assembly would be sufficient for this application?
Thanks for any suggestions....
A channel shape works best for the beam design due to space constraints. In my situation, I would utilize a channel shape with the 'C' pointing to the ground, lift at the center bottom to lift a equal load on each end at the top.
Looking at moment of inertia and weight per foot, I would be much better off using 2 unequal leg steel angle iron sections to form a channel shape versus using a common steel channel. Obviously the longer legs would be in the vertical direction to increase strength.
My question is how to weld the channels, and would this arrangement result in strength comparable to the sum of the moments of inertia of the two angles? I believe welding a 1" deep weld each foot length along the entire length of the angle iron assembly would be sufficient for this application?
Thanks for any suggestions....






RE: Beam design and deflection
maybe C-channels connected to the web plate.
I'd like to have the load carried in shear, like having a C section wrap around the beams, and weld on the vertical webs. or C in the middle and run the beams on the outsides ... lot's of variations.
size of weld depends on size of load ...
another day in paradise, or is paradise one day closer ?
RE: Beam design and deflection
Anyone know approximately how much weld conservatively needed to match up to the load, say 2000# load how much weld to hold this together?
RE: Beam design and deflection
Any chance of a sketch, I can see how you are going to connect to angle sections together to form a c channel, what I cannot see is how you get a 1" deep weld on the thickness of the angle toes.
RE: Beam design and deflection
BA
RE: Beam design and deflection
Hopefully the quick sketch comes through as readable.
RE: Beam design and deflection
Why not just weld some vertical ribs to increase strength of the original channel section you proposed.
I'm not a big fan of stitch welding particularly on lifting equipment I prefer continuous welding and from your sketch your weld can only be as deep as the section thickness
RE: Beam design and deflection
another day in paradise, or is paradise one day closer ?
RE: Beam design and deflection
1.) You will get a much stiffer section than you would with just two angles.
2.) You can avoid the welds. Personally, I am not a big fan of applying concentrated point loads to welds, as you have shown.
RE: Beam design and deflection
Desertfox- are you saying to weld outboard vertical stiffeners to a standard channel to increase the moment-like in using bar stock (I think this makes sense)?
As noted the point load would be only on the channel web, was wondering about this type of mod considering rb1957's comment about the shear path.
Actually I thought rb1957's suggestion as relating to my 'B' option sketch is the most robust reinforced design, and assume just add up the total vertical moments of the 3 pieces.
RE: Beam design and deflection
BA
RE: Beam design and deflection
Yes that's exactly what I'm saying, just weld some vertical ribs onto the back of the channel to increase the depth.
RE: Beam design and deflection
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RE: Beam design and deflection
don't know why you can't close off the bottom of the angles (and make a box section ?
another day in paradise, or is paradise one day closer ?
RE: Beam design and deflection
RE: Beam design and deflection
RE: Beam design and deflection
I may just go with a channel that is heavier than what is needed to be conservative. In this application the 'C' shape will be pointed down and the single point lifting load will be under the center (inside the 'C'). The load will be distributed over approximately 1/2 of the internal width of the channel. The load I am picking will be at the top at both ends, also in the center of the channel width and distributed over about 1/2 of the total channel width.
I will be using a beam with calculated deflection ~50% of the 1/240th of the beam length (I have read 1/240 is acceptable for beam deflection).
One last question: Is there any issue with the loading on a channel being centered on the web, creating a problem with stress tranfer to the vertical members in this configuration?
I can sketch if anyone wants to look at the actual configuration... Thanks
RE: Beam design and deflection
RE: Beam design and deflection
RE: Beam design and deflection
I was considering testing the selected channel and measuring deflection as I apply the lifting force. My thought was that if the deflection matches the 50% level as described above I should be fine??
Could there be catastrophic failure if the deflection is tested to be conservative?
RE: Beam design and deflection
BA
RE: Beam design and deflection
According to the AISC 2005 spec, yielding will control for most of the channels currently manufactured with 36 ksi steel. So typically, flange instability is not an issue since most of the channels have stocky flanges. However, there are a handful of them that are classified as slender with 36 ksi steel. Therefore it would be worth your while to check to make sure the one you are using does not fall into this category. Table 1-6 of AISC will tell you which ones are slender. Also Section F6 of AISC will give you more insight into channels bent about their weak axis.
If the flanges were to buckle, than yes that would be considered a "catastrophic failure." However, as I mentioned above, most channels will yield before this happens. Still worth checking though.
Load testing the channel couldn't hurt, especially if you are limiting the deflection to half the allowable. However, I'm not really sure what your ultimate goal is here with this beam.
I would also check into any special loading requirements you may need to include in your design i.e. impact loads, etc., since this is a lifting beam.
RE: Beam design and deflection
BA
RE: Beam design and deflection
Just a thought if you are going to use the existing channel why can't you turn it upside down so the vertical legs are in tension instead of compression.
RE: Beam design and deflection
I am looking at rectangular tubing also, the extra height makes things more difficult but sounds much less risky!!
RE: Beam design and deflection
1) Lateral torsional buckling is a concern. Using a tube section would address that. So would using a a channel or a pair of angles so long as the composite section is bent about its weak axis. If you use a channel or angles, I would ensure that bending is about the weak axis.
2) Whether you use angles, a channel, or a tube, I would highly recommend using a stocky bearing plate at the points of load and support to distribute the loads out to the vertical, shear resisting elements of the cross section.
3) Don't be spooked by the flange buckling business. You don't need software or voodoo mathematics to evaluate it. You only need to ensure that the width to thickness ratios specified in the AISC manual are not exceeded.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Beam design and deflection
another day in paradise, or is paradise one day closer ?