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How to strengthen I beam deflection 1

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Tnewbon57

Tnewbon57

Structural
Apr 7, 2015
6
Hi all,

I have a unique problem that I have been asked to solve and would appreciate some input from a more experienced group. I have been tasked with strengthening an existing structure made with two 6" X 6" square tubes as vertical posts supporting a 40' long (10 X 30) I beam horizontally, the tricky part is that this structure is holding up 8 heavy punching bags on trolleys. I need to strengthen the I beam without adding anything to the under side of the beam as it would inhibit the trolley. any thoughts would be greatly appropriated, thank you.
 
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You can take most everything here and apply it to the top flange rather than the bottom: Link. I imagine that your beam will be laterally unbraced along its length however.

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.
 
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This is a good source for manually cranking out I values for custom shapes. Try different configurations of the existing beam (known Ix) and your two WWF sections (Known Ix), adding them to different places on the beam.

Long story short and going back to beam theory, you will want them as far away from the centre of your existing beam as possible.
 
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make that your two tube sections. I either need to start proof reading, or get more sleep.
 
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The classic solution is to weld a channel on top of the beam. This increases the section modulus, moment of inertia, and allowable unbraced length. Often used on bridge crane beams. Here is a typical view:

638160282_730.jpg


[idea]
[r2d2]
 
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If it garners sufficient stiffness, I think that SRE's method will be the way to go.

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.
 
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I think the SRE's suggestion is a good one :) , but i would think in something else in order to avoid the overhead weld position, it could be a cover plate shorter than the beam flange width.

Regards
 
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I was thinking plug/slot welds from above.

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.
 
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Well, i will depend on the beam deflection ratio. Of course it is a great gain with the channel, but i think is easier and more economical the cover plate.

 
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LuisUgarte - Completely agree that a cover plate that is not as wide as the flange is simpler to weld and would increase the beam's "S" and "I". The big advantage of the channel is to increase the allowable unbraced length. A narrow cover plate would not help much. For the OP's problem, 40' is a long span for a 10" beam - increasing the unbraced length may be important. On bridge crane applications that is the primary reason to use the channel.

KootK - Plug welds is what I am thinking, too.

[idea]
[r2d2]
 
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Is it insufficiently strong or insufficiently stiff? If stiffness, which direction is greater stiffness required? Also factor in the extra weight and the potential for pre-forming the piece so it deflects vertically to be straight under load.
 
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You will only be stitching it together, so welding the channel will work just fine IF you flip it over. Maybe even use a C8 so it is sightly narrower than the flange.
Alternatively, putting the right tube on top could easily solve both lateral and vertical deflection. 3D makes a good point... Jack up the middle of the span with shoring posts to level or a slight upward camber before welding the new section to it.
 
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Thank you all for this great advice. The up and down deflection is not a problem, only the lateral. C channel is what I was thinking as well, and I am a structural welder so attaching it would be no problem.

I did have one other thought. If I were to add Angel iron to the inside of the beam over the web (like a square tube), would this strengthen the lateral deflection? it would be cheaper, and easier to manage the assembly.
 
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What about the skinny support tubes? Even a little bending in those will give some good sideways movement to the beam.
 
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Every little bit helps, but if you want to make a big difference, add the cap channel.
 
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You haven't measured what contributes to the sideways movement. Proceeding without knowing is risking spending time and money on an effort that doesn't help. It may be that adding diagonal bracing to the verticals is required; if they are the source of unwanted deflection then no amount of stiffening of the I-beam will make a difference. What's the resonant frequency for both verticals in phase?
 
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3DDave the verticals have no vibration, they both have diagonal kickers, and there is no movement in the I-beam at the point it is attached; as well it is visibly apparent that there is no up and down deflection. the sideways deflection is from the swinging of the bags, and toward the center point the beam seems to rotate a little bit, but there is no bounce. Angular supports are an additional consideration.
 
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Given this additional information:

1) A tube on top would limit rotation.
2) Your idea with the angles also would limit rotation.
3) If tolerable, an extra mid-span column/diagonal might be your biggest bang for buck. It could probably be detailed so as not to interfere with the trolly.

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.
 
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