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Will the LVL Microllam beam I made replace a W8x35 steel I beam for a 20 foot span? Question
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Posted by: ray

03/12/2006, 14:11:35

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I have a 20 foot open span on the first floor of a house that needs to support a second floor. Above the span are 2 bedrooms.
The 20 foot span was supported by a 2x4 stud wall, with the stud wall setting on a steel beam which in turn was supported by the concrete blocks of the foundation. The floor joist for the second floor met above the 2x4 wall on 16 inch centers.

I was going to replace the 2x4 stud wall with a W8x31 or W8x35 steel I beam which the architect approved to carry the weight. That I beam would be supported by a steel post on each end. The posts are fine - I'm not worried about them at all.

Instead of the steel I-beam though, I decided to make my own beam out of Microllam LVL. So I have four 1 3/4 x 8 1/2 inch by 20 foot long LVLs which I nailed, glued and bolted together to form my beam. Total dimensions on the LVL beam then are 7 inches wide, by 8.5 inches tall by 20 feet long.

The bolts I used to hold the four together are 3/4 inch thick, in the center and are spaced roughly four feet apart down the beam, and where the bolts go through the beam I have 8 inch square plates on each side with a 3/4 inch hole in the center to accept the bolt, so I could really tighten up the bolts without hurting the Microllam.

Two questions.

Is my design strong enough to carry the load?

If not, would replacing my 8 in square plates, with two flitch plates on each side that would be 1/4 inch thick by 8 inches tall by 20 feet long and bolted through the beam with 3/4 inch bolts at 6 places or so along the beam make my design strong enough?

Snow loads if you are looking up info on tables are those in the Pittsburgh, Pennsylvania area of the country.

Many thanks to any and all for their opinions and advice.

I have my beam in place but its supported now at four places (the two end posts and two jack posts spaced evenly down the length of the beam) so for now I know its just fine to carry the load. I want to take those two jack posts out of the middle though, and before I do I thought I'd better check myself.

Also, if too many of you think my beam won't work, I can still put the steel beam in. Its just that this was so much easier to build in place than to try to lift a 700 pound beam up in the air and put it on the end posts.

Many thanks to all who respond!!!!!!!!!!!!!!!!!!!!!!!!

Ray








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Re: Will the LVL Microllam beam I made replace a W8x35 steel I beam for a 20 foot span? Smile
Re: Will the LVL Microllam beam I made replace a W8x35 steel I beam for a 20 foot span? -- ray Post Reply Top of thread Forum
Posted by: sangrover

05/20/2007, 06:40:03

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Ray and all,

I just came across this original post on the 20' span with an LVL beam, and was wondering how it is working out? Did you take the two jackposts out?

I have an absolutely similar situation as Ray (read above) -- the only difference being I am dealing with a 12' span. And with my only qualification being a homeowner with a credit card account at homedepot (and no structural engineer/architect background), I thought I'd wait to hear what you or others have to say before I decide to take the stud wall out! I was thinking of replacing the existing 1st floor stud wall with two 2x12 beams, resting on steel columns or 4x4 columns.

many thanks to all for responding!
-sanjay







Modified by sangrover at Sun, May 20, 2007, 06:53:34


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Re: Will the LVL Microllam beam I made replace a W8x35 steel I beam for a 20 foot span?
Re: Will the LVL Microllam beam I made replace a W8x35 steel I beam for a 20 foot span? -- ray Post Reply Top of thread Forum
Posted by: jstahlman

03/25/2007, 15:02:30

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Do Not Remove your center supports. Your LVL beam is woefully inadequate and is subject to STRUCTURAL FAILURE. Your best bet is to sandwich a couple of steel flitch-plates---possibly a couple of 5/16" or maybe 3/8"---without knowing the exact load conditions its hard to say. ---For future reference: a rule of thumb for sizing a wood beam is 1" of height per foot of length. Also it's a good idea to keep your Span-to-Depth Ratio below 20.







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Re: Will the LVL Microllam beam I made replace a W8x35 steel I beam for a 20 foot span?
Re: Will the LVL Microllam beam I made replace a W8x35 steel I beam for a 20 foot span? -- ray Post Reply Top of thread Forum
Posted by: swearingen

03/12/2006, 15:38:52

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You asked the question, "Is my design strong enough to carry the load?". I don't know the answer to that question, because I didn't do the numbers yet. I do know the answer to this question, though: "Is my design stiff enough to not sag too much?" The answer is no way. In fact, a W8 steel beam is a fairly short member for that span. If you knock out those two jack supports, that beam will sag tremendously and due to the nature of creep in wood over the long term, it will only get worse. You really must find a local, competent, structural engineer that can come and look at what you have. He'll be able to make a determination on strength AND stiffness, which are both equally important when designing these types of beams.

Don't wait for more votes on this; I'm telling you this beam will not work. A quick side calc based on generic numbers shows that your floor will deflect on the order of 1 1/2" which will grow over time and is already way over allowables. The code limit to reduce discomfort over visible sagging and cracking in plaster or sheetrock walls is 1" (L/240) and the normal threshold for design is 2/3" (L/360). Make the beam out of 2x12's or get a light W10 steel beam (it will actually be lighter than the W8's you mentioned) and you won't have this problem.








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