Beam retrofit
Beam retrofit
(OP)
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.
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.






RE: Beam retrofit
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 ?
RE: Beam retrofit
RE: Beam retrofit
RE: Beam retrofit
RE: Beam retrofit
RE: Beam retrofit
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
RE: Beam retrofit
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!
RE: Beam retrofit
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.
RE: Beam retrofit
RE: Beam retrofit
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 retrofit
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.
RE: Beam retrofit
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 retrofit
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 ?
RE: Beam retrofit
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.
RE: Beam retrofit
RE: Beam retrofit
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.
RE: Beam retrofit
RE: Beam retrofit
RE: Beam retrofit
RE: Beam retrofit
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 retrofit
That's precisely why I asked the level of increase required. If he needs a ridiculously substantial increase, then I don't think there's a better option but remove and replace. If minor, there's likely a few option without welding that we could come up with.
RE: Beam retrofit
2 questions:
1 - How are you guys describing stiffness (units, thoughts)...
2 - How would the orientation of the C-Channel likely be?
- back of channel to web of IPE
- flange of channel to web of IPE
RE: Beam retrofit
Consider welding additional plates to the underside of both the top flange and the bottom flange of the existing WF beam. Remember to bevel the inside corner of the top plates to clear the radius of the beam web/flange.
The welds do not need to be continuous. Intermittent fillets are usually sufficient. One must calculate how much and what size fillets are needed.
Best regards - Al
RE: Beam retrofit
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 retrofit
Is remove and replace really not an option? That's a fairly large increase required. It's also surprising that you need that stiff of a beam, but strength and vibration are non-issues.
RE: Beam retrofit
another day in paradise, or is paradise one day closer ?
RE: Beam retrofit
RE: Beam retrofit
RE: Beam retrofit
May be you find it a economical way to reduce deflection. (Another Whacky alternative...)
Note: The Supporting Beams's capacity need to be validated for these addition moments which got transferred to it due to moment connections.
Cheers! -VH
RE: Beam retrofit