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Structural engineers
General Boards - The Lounge
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Structural engineers


Mar 21, 2024, 9:02 AM
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How much deflection is normal for an 18' LVL beam? 9"x 4"

Thanks for your professional opinions that I'll hold you to forever.

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LOL


Mar 21, 2024, 9:09 AM
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Axeing the Jounge for professional opinions.

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It's my trusted source for professionals***


Mar 21, 2024, 9:10 AM
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I'm not a structural engr, nor did I stay at a HI express lass night, but


Mar 21, 2024, 9:18 AM
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HTH



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It doesn't


Mar 21, 2024, 9:19 AM
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I don't math.

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Sorry. I tried.***

1

Mar 21, 2024, 9:23 AM
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his situation is #4


Mar 21, 2024, 4:39 PM [ in reply to I'm not a structural engr, nor did I stay at a HI express lass night, but ]
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w=15 psf * 8 ft
l=17 ft
e=2100000 psi (That's what the 2.1E is in the picture)
I = 1/12(5.25)(9.25)^3 in^4 (I = 1/12bh^3 most engineers will recognize this from mechanics of materials)

You plug all those numbers in and the correction factor is 1728 and you should come up very close to the 3/8ths inch that I came up with below. I used the weight of the beam too so this will be slightly lower.

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Seven. Eight with enough lube and patience.***

2

Mar 21, 2024, 9:21 AM
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Moisture content is often overlooked***


Mar 21, 2024, 10:47 AM
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7 is correct

2

Mar 21, 2024, 12:57 PM [ in reply to Seven. Eight with enough lube and patience.*** ]
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How much weight are you putting in the

1

Mar 21, 2024, 9:30 AM
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sects swing?

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That's in another place***

1

Mar 21, 2024, 9:44 AM
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Allowable current code deflection for a floor is

4

Mar 21, 2024, 9:37 AM
Reply

.6 inches for an 18 ft beam. Half that for a roof beam with no ceiling. I would design it for .45 inches, which is industry standard for engineering lumber.

You might want to remeasure. Nobody makes a 9"x 4" LVL, more likely it's 3.5" x 9.25" if it is an LVL or 3.5"x9" if it is a glullam.

9"x4" means it is laying on it's side.

You can hold me to this forever because physics doesn't change.

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was going off memory


Mar 21, 2024, 9:43 AM
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It's 9.5" x 5.25" ish.

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reverse that since it's not on it's side lol***


Mar 21, 2024, 9:45 AM
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take a picture of it

2

Mar 21, 2024, 12:38 PM
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Measure width and depth. See if there are any markings on it and measure the room width above it and Ill tell you whats going on.

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Re: take a picture of it


Mar 21, 2024, 12:46 PM
Reply

5.25" wide (3- 1.75" beams together) x 9.25" deep x 17' long.

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Now

2

Mar 21, 2024, 1:21 PM
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What is the distance from the drywall in photo #2 to the wall on the other end of the floor trusses that are supported by the LVL. Drywall to drywall or garage door or masonry wall what ever is on the other side.

One last thing, are there any walls or posts on the floor able that carries load down through the floor trusses?

This looks like it might be a garage or walk-out basement. You might have some walls that are non-bearing. You most likely have roof trusses since you have floor trusses and unless the roof is a crazy shape only the exterior walls will be load bearing.

My gut tells me the LVL is undersized at 17 feet because floor trusses tell me the span is probably around 25-30 feet with the LVL in the center.

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16' span, sitting on the poured exterior walls


Mar 21, 2024, 1:43 PM
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There is a load bearing wall that splits that at 12'3". so you hav 12' one side and 4' on the other.

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Re: 16' span, sitting on the poured exterior walls


Mar 21, 2024, 1:56 PM
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So there is a load bearing wall that is directly above the LVL? What is it holding up? Floor? Roof? what is the width from the load bearing wall to the next wall on both sides?

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No.


Mar 21, 2024, 2:41 PM
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Above the beam is the kitchen.

The trusses sit on load-bearing walls that are 12' and 4' apart. The beam is about 8 feet from the farthest load-bearing wall.


So from left to right:

Load bearing poured wall > 8' to LVL beam > 4' to load bearing framed wall > 4' to load bearing poured wall.

Above the beam is the kitchen.

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You guys. Seriously! Why hasn't


Mar 21, 2024, 2:43 PM
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bobbyBuildsIt been asked these questions?

I get he doesn't have a bow saw. I do. I just don't think it would be needed for this, at least at this stage.

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Bigthump builds it has been building

3

Mar 21, 2024, 2:49 PM
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Okay, here is your answer

3

Mar 21, 2024, 4:24 PM [ in reply to No. ]
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I don't ever do structural evaluations unless I actually put my eyes on it. I don't ever want to be in front of a judge when someone was hurt and him ask me why I didn't put my eyes on it. I do way more of these than I want to, but figuring stuff out is sometimes fun. When there is a problem that nobody can figure out, it makes it to me often. I do a hundred or so a year and it is about 10% of my billing.

I see this problem often under kitchens. Building code requires us to design houses for 40 psf. Yet kitchens are usually much higher load in reality. There is often a big island with a heavy slab and cabinets in the center of the room and refrigerators and cabinets filled etc.

With just the weight of the structure and nothing else, I'd expect that beam to sag about 3/8 th's of an inch. If there is a center island and/or cabinets you can double that to about 3/4 th's of an inch

Loaded to code with people up there during Christmas and I'd expect 1-3/8th's of an inch.

The beam is undersized by code. If I was designing this beam, I'd use minimum (3) 1.75 x 11.875" deep.

The way to fix it is to add a post in the center (usually not desirable) or add 2 more plys to the beam. Jack it up just a little and then add a ply on each side with the connection pattern below.

You aren't supposed to have a 5 ply member, but we don't have a choice here without getting expensive. I'd add each ply with two rows of Simpson SDS screws 6" long 24" on center and stagger them 12" from one side to the other so that the screws are not in the same location.

One last thing. It looks to me like they did not nail the trusses to the top of the lvl. Each truss should be connected. They could have shot down through the top of the bottom chord, but since they didn't use an engineer to size the beam they might not have built it right either.

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Deer all structural engineers

3

Mar 21, 2024, 10:32 AM
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I like your funny words magic man


We have to know the max weight of the guy you're going to...


Mar 21, 2024, 12:29 PM
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condemn to walking it when he upsets the pirate leadership.

Imo, deflection isn't a problem unless you're trying to restrict the condemned's ability to spring off and turn it into a diving board.


Message was edited by: ClemsonTiger1988®


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Replies: 25
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