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Too much camber! 3

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jerseyshore

jerseyshore

Structural
May 14, 2015
713
Came across a new one. A local registered design professional sized a EDIT: W18x175 to span 32 ft clear across a new house. The problem was they also specificed an additional camber of 1/2".

Well, guess what, they put it up and it was bad. Not sure if the 1/2" camber was in addition to any natural beam camber (I'm not camber expert,very very rarely do I specify it), but it was humped pretty badly in the middle.

Normally we get called in to reduce deflection, not increase it. They framed the 2nd and 3rd floors and that thing didn't budge. Yes not all of the dead load was on it, but even with the full 15 or 20 PSF at each floor I don't think that's going to make a difference.

Any creative thoughts on how to get this thing close to level?
 
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1. Stick a strop around the middle of it and tie it to something very solid. Get a blowtorch out and start heating the cross-section at various points
Maybe it softens enough to drop

2. Could also put horizontal slits in the flanges at various points with props underneath it to try and get it to sag to flat, then weld in new plates equal thickness to the flanges, make good coatings

3. Check the end conditions and see whether accidental fixity has been generated - perhaps the design calcs were based off simply-supported models that are not reflected in reality
Perhaps undoing a bolt at the end will release some deflection and then the fixing can be reinstated

How important is the actual camber anyway, can they just build it out by packing everything? Same principle as packing out an uncambered beam that sags but in reverse

Probably should check the actual camber anyway to figure out who made the stuffup - 1/2" camber for a beam spanning 32ft seems reasonable without understanding anything of the properties of a W18x187
 
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jerseyshore said:
Any creative thoughts on how to get this thing close to level?
Click to expand...

Add a post support somewhere in the middle 1/3, cut the flanges to drop the beam, and clean up the connection to the column?
 
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This may be a dumb question, but what is a W18x187? I am not familiar with this size, is it custom-fabricated? If it is what I am picturing, then I can't imagine why it would be cambered in the first place. Usually, it is not recommended to specify any camber smaller than 3/4", just increase the size of the beam a bit instead.
 
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I got the sense that they don't want to waste any time so they'll just have to get the framer to shim it level as best they can. Kind of a pain with the precut studs because now the interior is going to be 1/2" higher. Not sure if they'll try to level the entire floor out all around or just live with a slight hump.

The end condition is just a knife plate with 5 bolts. And they definitely don't want any new interior columns since that's why they are putting this massive beam in. Replacing it isn't an option just based on timeline and cost. Not like these steel places have W18x187's on the shelf.

Apparently the non-engineer registered design professional uses Beamchek (which is very popular among non-engineers around here) and it has a little click box that says "Add camber" or something along those lines.

EDIT: W18x175 is just a massive beam. Super rare obviously, especially for a house (hell the W12x26 in my living room is super rare so idk what this is considered then).
 
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If it was 'humped pretty badly in the middle', they probably over-cambered it. I understand that it can be hard to achieve such a gentle camber in practice, especially with a large beam. There's no way you would even see a 1/2" camber over 32', that's ~L/750.

 
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I was thinking the same thing bugbus must be something more happening here.

Also feels very shallow for the span. A W24 would probably get there just as well and be a lot lighter. The shape is a great column, not a very efficient beam to begin with.

Any means of reducing the span feel like more trouble than its worth for L/750 (if thats really the case).
 
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If it was a dropped beam, you
Could post tension the top flange to bring it down. It's probably a flush beam though and, either way, PT would take some time.
 
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The whole house has 11 7/8" TJI's so every other beam is W10 or LVL/ flitch to be flush. This one literally splits the entire house in half so they have no columns on the first floor, hence the use of a W18x187 top flush to keep it as shallow as possible.

I definitely agree with the over-camber comment. That was what I said as well. I asked them for an accurate measurement from high point at middle to low point at ends. I didn't believe them at first because you guys are right, 1/2" shouldn't be noticeable.

One of the first steel beams I designed as an intern was a W8 that spanned 20+ ft. It calced out so I showed my boss and he taught me the half-the-span inches rule of thumb, saying even though it may work on paper, it's not going to look right out there. This is just the reverse of that. Seeing one of these uncommon thick beams always makes me double and triple check the situation because I just know it ain't going to look right.

 
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Ugh I must be too tired, the rule of thumb is 1/2 x span for steel and the span length in inches for wood. Right?

So W18 for that span should be just right. Must have a lot of load to get x187 though.

Now that its loaded and if shoring isn't an option tough to imagine safely compromising the stiffness enough to get the deflection needed to level the beam.

 
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Heat straightening might work for your situation. I think it's what greenalleycat mentions in item 1. I haven't seen it done;it's somewhat of an art form that might have a few practitioners in your area.

 
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If the wood can handle it, gypcrete the floors. Add dead load and level the floor simultaneously. Probably easier said than done, of course...
 
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What kind of house would require a beam of that size for that span? Seems a bit off.
 
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I don't believe W18x187 is a real size...typo by chance? I don't see it in any AISC resources.
 
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Call the "local registered design professional" and ask him what he was thinking trying to camber a big beam like that such a small amount. If you call AISC I believe they would say "don't do such a thing" for exactly this reason.

How about you flip the beam over so it's sagging and then shim everything up?

And I agree that there is no such thing as a W18x187 or W18x87.
 
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Heat straightening is a common practice to straighten long shafts. Heat is applied with a torch to various spots. Those spots will expand with heat, then plastically deform in compression due to high temperature. On cooling the spots shrink and induce an internal tension force in the metal. This causes bending so the spot is on concave side of the bend. It is an art, but can be done with precision.
 
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Agree with heat straightening. This is usually done either at mid point or third points depending on length and amount of camber. As others have said, I don't believe W18x187 is correct, but if it is in that realm, it has around an 1-3/4" thick flange that is almost 12" wide - It's going to take a lot of heat input. If you are already framed above it may not be the best idea, definitely have a fire watch.
 
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If it was 'humped pretty badly in the middle', they probably over-cambered it. I understand that it can be hard to achieve such a gentle camber in practice, especially with a large beam. There's no way you would even see a 1/2" camber over 32', that's ~L/750.
Click to expand...

Definitely over cambered. One of the main things with Camber is that you ONLY want to camber out the real dead load. If you were to include LL and dead load that doesn't really exist (because you were very conservative with your assumed dead loads) then you're going to have problems like this.
 
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I'm surprised you would notice a 1/2" camber on 32' (didn't notice your posting Josh)... Did anyone measure the amount of camber? Chalkline? It's a huge beam... supporting the entire house? [ponder]

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik
 
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