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# What is an acceptable span for an 8" steel I-Beam?

#1
10-02-04, 03:11 PM
Ardayon
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What is an acceptable span for an 8" steel I-Beam?

My rambler has a 22’ x 22’ partial basement. Down the middle runs an 8”x4” steel i-beam. The beam only extends into the room 19’ supported by a 4” post at the end and another post 7.5’ from that one. I want to move the middle post to create an unobstructed 14’ span. Can the beam support a 14’ span?

#2
10-03-04, 05:59 AM
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I would say yes, but I would definitely run this by a qualified engineer prior to starting on the project. Might want to post this up in the Architecture & Codes forum and see what Doug and the crew up there have to say.

#3
10-03-04, 10:21 AM
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No

Without having a qualified engineer examine your property to determine the loads for the span, the answer is no.

#4
10-03-04, 11:18 AM
Ardayon
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How about a simple reality check?

Originally Posted by homebild
Without having a qualified engineer examine your property to determine the loads for the span, the answer is no.
Homebild,

While I do understand your cautious sentiment I am trying to better understand the issues. Ultimately, this becomes a mathematical equation. Certain values in that formula are fixed such as how much load can this beam carry. Certain values must be estimated such as dead load and live load. The first pass of the number crunch will determine feasibility. If this project is well out of spec, other engineering alternatives must be considered such as strengthening the beam. Before moving such a critical structural member as a post, one must be certain the footing beneath the new location is sufficient. Although this is a relatively simple task to accomplish, I do not consider it trivial. That is why I turn to this distinctive forum for insight and guidance.

#5
10-03-04, 10:11 PM
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Insight and guidance, yep that's us!

I'm going to move this up to Archt & Codes and let the experts in the field pass judgement on the plan.

#6
10-04-04, 09:12 AM
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Ardayon,

I guess I'll say my 2 cents worth here.

Right off, IF your home has a truss roof system, taking roof load to the building perimeter, then we are talking about 11,500 lb load on the beam. Based upon the current posts in place, I agree with homebild, that your cirmcumstances will not provide for this large of a span.

There are 3 sizes of 8" beams, in general, each with different weights and flange thickness from 3/16", 1/4" and 5/16". There are others but these are more common to "standard residential" needs. The issue is that the home has the posts placed accordingly, then moving these will exceed the beams integrity and the load deflection will be in excess of current limits as what was approved for your home construction.

I would suggest that someone look at this, like a structural engineer, as this is the best answer to your question.

My thought is that if you intend to provide the 14' clear span, use an 8" beam, that is 6 1/2" wide - a W8x24. This could handle a 14' span, IMHO.

Thanks for your compliments on this Forum,. we all, members and moderators alike, strive to help each other with honest and helpfull responses.

Just some thoughts

#7
10-04-04, 09:45 PM
Ardayon
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The house does indeed use a truss roof system and the flange is 1/4" thick. From the wall to the first post is already an 11' span so I only need to coax a few more feet of capacity out of it. It has been suggested to strengthen the beam by bolting more steel to it. How much strength is lost by drilling holes to attach more metal? Replacing it is not a viable option since it continues through the wall and under the crawl space the entire length of the house. Any options for running another beam/LVL along side?

#8
10-05-04, 07:25 PM
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Bolting Not an Option

Bolting is also not an option since it is against most codes to drill or notch any beam.

What you "might" be able to do, however, is to WELD additional plates to the existing beam to strenghthen it and add to its span.

But the bottom line continues to be that you cannot guess at this or look to the web for answers when the only authoritative answers you will get are from code and engineering professionals who can actually view your home, calculate your actual loads, and determine whether your beam can span what you'd like it to span.

Call the professionals and get the correct answer.

#9
10-21-04, 10:37 AM
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Join Date: Oct 2004
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You won't imperil the structure, but...

Theoretically, increasing the span from 11 feet to 14 feet should increase the beam deflection by a factor of 2.5 for similar loading (not exactly the case here, as you're re-loading the beam more to mid-span). Which could possibly be a code issue as you would need a current deflection of L/900 to end up above L/360. If the floor above is rock solid right now, give the engineer a call and go for it.

#10
10-25-04, 06:50 AM
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1) hope for the best

2) strengthen the existing beam

3) add on another beam to existing

will not work unless you get someone (a professional) to tell you what you can and can't do. stop cheaping out - hire someone. what you want to do CAN be done, but it costs money.

#11
06-05-05, 08:38 AM
T-Square
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I could not pass this one up, and had to comment.

I've seen alot of homes built like this. It's my guess, the house is 22' x 45' with 23' of crawl space. And I bet the I-beam is short of the foundation wall, carried on two 4x8 posts sitting on 2'x2'x12" footing pads, and are 18' apart. Where the beam is a 40 footer!

There is only one 8" x 4" I-beam and its a 18.4 #/ft. with a .270 web thickness.

It seems that only two 4x4 posts on the basement side are hardly enough to support this beam. I would of asked, "What was directly above the second 4x4 on the first floor?" A bearing wall? maybe!

It's also my guess the Builder cut corners, or never installed a 4" concrete lally column, at the end in the full height basement. And the second 4x4 was added to take the bow out of the other 4x4.

I would of advised adding a Lally column this side of the crawlspace wall, where there is a footing, and replace the end 4x4 with a 4" Lally column's, each with a 6"x6"x 3/8" base plate w/ four 9/16" holes. Since the span between the second 4x4 and the next in the crawlspace did not deflect. The span between the two new Lally column locations won't either. An 8"-18.4# I-beam has an avg. flange thickness of 0.425 is pretty ridged about its neutral axis, of y-y and x-x, with the top flange in compresion and bottom in tension. Even an unsupported end would resist rotational twist and sag. And the owner would of gained the clear space he needed. With a minimum amount of welding at each column to flange joint, with 1/4" fillets 1 1/2" long, 90 degrees apart. Would not effect the beam at all, and solve the problem with less cost to the owner.

No one asked if the 2x12 floor joists overlapped on top of the beam, or if they were I-joists? And what their c to c spacing was?

But then again my comments are after the fact, and may be moot points and assumptions on my part. But, I wonder how close to actual conditions I really am? And what was done to resolve the problem since the first post.