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#### flyboyz

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I am trying to replace a load bearing beam. It is currently 3 2x10's (doug fir) and it runs over a 10 foot span. I would like to install a tee beam (flange down) that measures: web 8.5", .300" thick and the flange is 6" and .425" thick. I'm pretty sure this new beam has more strength but I fell asleep in math class and can't verify this. I can get a beefier beam but would like to keep the weight down. Any help would be great.

#### Daniel Holzman

· Civil Engineer
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Presumably this is a steel t-beam, but you don't say that, so perhaps you can confirm the material. The strength of a steel t-beam depends on the yield strength of the steel, so you need to know that in order to do the analysis. You are proposing an inverted t-beam, therefore the top flange is effectively the floor, so you need to design the structure so that there is adequate connection between the floor and the web of the t-beam.

#### flyboyz

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I guess I forgot to mention that. Yes, it's steel. It's actually an I-beam that is cut in half. I can get it in either ASTM A-36 or A-572 grade 50. I was planning on using the A-36 but could upgrade to the stronger if need be.

I don't understand what you mean by making sure the floor is attached to the web. Is that the weak spot in the structure? The load will be on the flange, the web giving it the rigidity I assume.

#### Daniel Holzman

· Civil Engineer
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Maybe I did not understand your post. You said the flange would be down. I assumed you meant that the flange would be on the bottom, and the beam web would support joists above it. But maybe you have a different geometry, maybe post a diagram of what you plan to do.

My point about the t-beam is that unlike an I beam, a t-beam has only one flange, so the t-beam has to be protected against web buckling since part of the web is in compression, and there is no flange to support the web (on one side). This makes t-beams harder to design than an I beam. Usually the side of the t-beam with no flange is supported by the floor, which requires careful detailing of the connection between the floor and the web.

#### flyboyz

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You are correct in your understanding of the flange down tee beam. The web would be under compression. Maybe I should explain my project. I have a one story house with a basement. The basement is the version that is only 7 ft tall. Retarded, I know. The span across the floor is made of 2x10's, 16" on center. There is a load bearing wall through the middle of the basement to support the span of floor. The floor joists are just overlapped a few inches and are supported on the wall. Mostly it's not an issue, but in one section it's open and the floor support is made of the 10' span of 3, 2x10's. That makes it a whole 6'2" of headspace. When you walk through at 6'1" tall, it's rather annoying as you can imagine. My idea was to run a tee beam up through the joists having them rest on the flange, (blocking in the ends of course) and tying the joists together above the top of the tee beam with a steel plate. That way I have removed the head bonking beam. Of course, I couldn't use an I-beam as it won't fit up with the top flange. I could cut the top flange at each floor joist you still have the weakest part at the joist with no flange.

The only other option would be to put an I-beam under the joists and make the web as short as possible. It might be better but still not ideal. Beating the house builder would make me feel better but I would still have the same issue:vs_mad:

#### Thunder Chicken

· PE Mechanical Engineer
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You're not interested in strength, you're more interested in stiffness/deflection. Properly designed wood and steel beams should limit deflection under a given load. If you're loading them to their strength limit, something is wrong.

I'm not sure a T beam does much for you. Web buckling definitely might be a concern. A standard wide flange I beam might be a whole lot less problematic and easier to source, and give you better clearance.

If you're willing to throw in some intermediate supports to half the spans, you could potentially use a shorter sistered wood beam.

I'd recommend that you speak to a structural engineer about this because this is an optimization problem - finding the shortest beam section that can span the same distance with the same maximum deflection. There are dozens of beams that will be shorter and do the job, you want the shortest. You're not going to get that optimum answer from a chat room. The calculation is not difficult, can be done on a spreadsheet, but if you can't do it then you should get an engineer on it. I'm assuming you'd rather not cause the house to collapse because of a math error.

But no matter what you do, you're only going to be able to shave a few inches of clearance, as beam stiffness is mostly driven by the vertical dimension of the beam. Using steel helps, but it isn't a magic bullet - the beam still needs a certain depth to be stiff enough to do the job, especially with the reduced cross sectional area of an I beam.

I think, for the cost and effort, you'd be better off to cover the beam in yellow protective foam and stencil 'HIT HEAD HERE' on it, or wear a helmet.

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