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Old 03-07-2010, 06:40 PM  
Shortmag
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Default Question regarding an existing beam being supported with a post...

Hi everyone... I'm new to the site and this is my first post.
I have a dilema, my 20' wide garage has a 4x12 beam across it, approximately 6' from the front opening of the garage. The second story of the home is supported by this beam. I have a post in the middle of the garage, 10' from either side, which supports the middle of the beam against sag. I want to somehow remove the post from my garage so I can park a vehicle in the middle and have two work areas, one on either side. Someone suggested using 1/2" steel plate which is the lenght of the beam and lagging it to the beam to help with the moment stength, to help with sag. Has anyone done anything similar, any help would be great.

Thanks for any advice, I know I need to most likely contact a structural engineer, but wanted to see if anyone else had a similar experience.



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Old 03-07-2010, 07:38 PM  
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Thanks for any advice, I know I need to most likely contact a structural engineer, but wanted to see if anyone else had a similar experience.
You answered your own question. And welcome to House Repair Talk.


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Old 03-07-2010, 08:02 PM  
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Don't just follow the suggestion by a "someone".

The loads on either end of the beam will be increased by about 50-100%, possibly requiring better support (possibly including footings) at each end.

When the post is removed, the strength capacity is dramatically reduced. Even with a re-enforcing plate, the deflection of the center of the support beam will be as much as 2", so the walls above can be expected to crack at the seams and doors will not work well.

This assumes the second floor does not become a temporary first floor.

Your gut reaction to get an outside opinion is very valuable.

Dick

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Old 03-08-2010, 06:32 AM  
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Here's the technical answer---

By removing the support post, you will essentially be increasing the stress and deflection in that beam by a factor of two. If you wish to increase the stiffness of a composite beam(steel + wood) back to the original amount, you would need to essentially double what is called the Moment of Inertia of the beam. A 1/4" piece of steel plate, 12" deep has the same stiffness/deflection strength as a 4" X 12" wood beam. This is because the Modulus of Elasticity(Young's modulus) of steel is 20 times that of wood. The problem is that a 1/4" steel plate fastened to the side of the wood beam would never work properly due to a problem called Lateral-Torsional buckling. A 1/2" plate would be more than enough strengthwise but may still suffer from the lateral-torsional buckling problem. If the composite wood/steel beam were braced properly(side to side) along the 20' length, the 1/2" plate addition would probably work just fine.

But I agree, the final solution should be analyzed by a registered professional engineer.

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Old 03-08-2010, 11:30 AM  
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Thanks for the replies... I'm going to have a structural engineer come out and look at the loads and draw up some plans for the permit. I just wanted to see what everyone thought. I appreciate your answers. Thanks

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Old 03-13-2010, 09:55 PM  
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So I had an engineer come out and check out my beam question. The easisest and cheapest version was to put a glulam sister beam anchored to the existing beam. Then install new support posts in the walls to support the ends of the sister beam.

Overall I think this sounds like a decent option that is not outrageously expensive. Thanks again for the thoughts

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Old 03-14-2010, 07:45 AM  
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put a glulam sister beam anchored to the existing beam. Then install new support posts in the walls to support the ends of the sister beam.
I wonder how many fasteners and in what pattern he will use to sister the two members.
Sometime, can you post before and after diagrams/pics? Thanks. I guess he is designing to an L/360 deflection or stronger.
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Old 03-14-2010, 12:27 PM  
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I'll post some before and after pics, along with the full specs of the project.

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Old 03-14-2010, 03:25 PM  
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I'll post some before and after pics, along with the full specs of the project.
Thanks. To make a 4x6 significantly stronger may take a pretty big Glulam.
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Old 03-21-2010, 05:32 PM  
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What size glulam did the engineer suggest? We have a similar situation in our garage and have a 3x20 glulam to add to our 6x11 beam and wanted to see if it would work.



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