Beam retrofit

[Leftwow]

Good Afternoon,

I am currently working on a modification to reduce the deflection on an 18' long beam. The load on the beam will be about 25 kips. My superior wants the to reinforce the beam in order to reduce the deflection due to operational loadings. I am thinking of unbolting the existing beam and replacing it. What are some ways of reinforcing a beam for deflection you guys have used in the past. Also, please see attached.

 

[rb1957]

your pic was not much help to me.

what happens to the structure if you remove a beam ?

if your boss wants to reinforce the beam in situ, and you don't understand why, then ask.
Once you understand the thought process behind the proposed repair you'll be in a better place to question the decision. don't default to "I don't understand why, it looks stupid, it must be stupid".

reinforcing the beam in situ depends on space and access constraints, how much of the beam needs reinforcing (if a displacement issue I suspect a lot of the span), how you guys like to work (weld or bolt on). and this may point to why repairing is a "bad" choice ... hundreds of feet of weld vs hundreds of bolts.

but what do I know ?

another day in paradise, or is paradise one day closer ?

 

[sbisteel]

Stitch weld a WT to the bottom flange? Increasing depth gives the most return for moment of inertia.

 

[Leftwow]

nothing should happen to the superstructure it's just spanning from one end to the other. Here is another attachment.

 

[jayrod12]

Weld 4 angles to the shape to increase the MOI, so it looks similar to the shape below. Keep in mind this is only effective if done before the loading has commenced.

 

[Leftwow]

So they would have to remove the beam, bring it to the shop... weld those angles on, then bring it back for reinstall.

 

[Lomarandil]

Not necessarily -- is field welding an option here?

Jayrod's solution can also be undertaken after load is applied, if the beam can be shored adequately during the retrofit.

(another option depending on access geometry would be to add a bottom cover plate. This will increase MOI and weld shrinkage would camber the beam upwards)

You could post-tension the beam to introduce an opposite moment, but for a beam this size, it won't likely be economic.

I'd also recommend an AISC webinar "Design of Reinforcement for Steel Members (part 2)" by Bo Dowswell:

https://www.aisc.org/content.aspx?id=37424

 

[BSVBD]

I agree with either sbisteel or jayrod.

sbisteel... the WT will increase your MOI... BUT... do you have room below?

jayrod... I've done this method many times.

sbisteel + jayrod... Can you do both?? Greater MOI! More $$$!

Leftwow... NO! You typically would not remove the beam. Field weld all steel in place.

Leftwow... Check you existing end connections when you apply the newly imposed 25K!

 

[jayrod12]

It could definitely be done in place, in fact it always is done in place. If you're going to remove the beam you may as well install whichever one you need. I'm just saying it can't already be deflected from the load at the time of installation.

This detail, the cover plate detail suggested by Lomarandil, and the WT detail suggested by sbisteel are all the same concept, you just have to determine which suits the current situation the best.

The WT detail is the most bang for your buck but comes at the expense of headroom.

Cover plates is second best in a strength per pound if you can add to the top and bottom flanges. A lot of the time the top of the top flange isn't fully accessible for a cover plate.

The angle detail usually works best when you can't add a cover plate to the top of the top flange, and you can't give up headroom below.

 

[Leftwow]

Well, there the problem is sometimes we have to get a hot permit, a lot of times if material is flammable around it you can either not acquire one or they would have to shut the plant down temporarily. So it is something common we have to deal with.

 

[KootK]

Print version of Bo Dowswell's stuff:Link. Decent summary of some of the options.

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.

 

[Lomarandil]

Jayrod, I was actually thinking of just the bottom cover plate. Figured the top is inaccessible.

KootK, thanks! I didn't realize it was also in article form.

LeftWOW:

If you can take the beam out (without requiring a plant shutdown, etc), just replace it with a bigger section like Jayrod suggests.

If you need to make a fix in place (with the load applied), sounds like you should find first if field welding or shoring are allowed. Many of the "easier" retrofits will require it.

If you're retrofitting in place without welding or shoring, there are (expensive) ways to add a bolted bottom cover plate or bolted post-tensioning "strap" -- but I suspect that a post-tensioning strand with bolted end brackets will be more economic for your scale.

 

[KootK]

If there's access etc, wholesale replacement may well be the way to go. Whacky alternative shown below. Maybe slip critical bolts.

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.

 

[rb1957]

do you guys like putting in hundreds of bolts like that ? I thought you preferred to weld ?

what sort of space limitations are there ?

If you want to reduce deflections, ie make the beam stiffer, I think reinforcing one side is not very effective (though the example of adding an I-beam clearly increases the depth of the beam); a simple way would be adding plates to the upper and lower flanges. If you need more, add Channels (ie plates with lips).

another day in paradise, or is paradise one day closer ?

 

[mike20793]

do you guys like putting in hundreds of bolts like that ? I thought you preferred to weld ?

Oh we much prefer welding to bolting, but I think the OP stated it may be difficult to obtain permission to weld since there is often flammable material around. Koot's detail may not be that bad, but field drilling all those holes may be difficult to make overhead.

 

[jayrod12]

We would be in a better position to debate the ideal repair situation if we also knew the existing beam size, and what the new requirements are.

 

[dhengr]

Leftwow:
You don’t say that this is a new load or an added load. You don’t say that the beam is over stressed, you don’t say that the connections are inadequate, or that there are vibration problems; why don’t you just shim up the load to the elevation it should be at so mechanical and piping connections and the like are o.k., and call it a day. Don’t forget that if you replace the existing beam, you still have to support the equipment load during this operation. And, you have to get those 18' long beams in and out of the plant. Maybe you could just install some post tensioning below the bot. flg. of the existing beam, harped down at the point of the load.

 

[Leftwow]

It's an IPE240, this will be a new load. The beam isn't overstressed, not sure about the connections yet. No vibration. Thank you guys for all your insight.

 

[JoshPlumSE]

You could turn it into a queen's post truss. It's kind of like post-tensioning for a steel beam. And, that would work even if the beam were already loaded.

 

[jayrod12]

What level of increase in stiffness do you need? Are you looking to double your stiffness, or only a 10% increase?