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shadetree 09-01-2011 01:52 AM

Replacing support post
The back storage addition to my new home has a post supporting the central beam that worries me. The post is out of alignment, with the bottom of the post about a half inch offset from the top. In addition, the post cap is far too small for the load it's carrying and is causing the wood above it to become noticeably compressed.

The plan is to support the beam (3x 2"x12"s nailed together, supported on both ends by 4 2"x6"s nailed together. Beam is warped slightly in the 13ft section due to the post initially being placed 15 feet from the right wall) above with two temporary jack posts while the old post is removed and for the week or two while the new pillar is curing. The new pillar is planned to be 12"x12" brick pillar filled with cement and an central threaded reinforcing rod that is secured into the slab. I was planning on using concrete brick instead of masonry brick for cost reasons.

I've tried searching for new metal lally columns in the Austin area, they simply aren't available.

Due to the beam being warped, I was planing to reinstall the old post that is removed with a new cap about 5 feet from the right wall to help reduce stress on the beam and eliminate the 13 ft stretch.

Some questions:

What would make good cap material for the brick pillar to distribute the load? I was thinking a single 2x12x12 with the wood grain perpendicular to the beam.

What would be the best way to lift the beam enough to remove the old post? Planning to get keep tightening jack posts up on either side of the lally until the girder is lifted the 1/4" or so and the lally is free.

Thanks in advance for any input!

oh'mike 09-01-2011 06:12 AM

Can you post a picture of the existing support?

How tall is the brick pier going to be?

Where are you? Local code might not allow a brick pier---Even if a permit is not required it is best to meet and even exceed the local code.

shadetree 09-01-2011 02:58 PM

I'm in Austin, TX. The structure was outside the city limits when it was built

It's 83" from the floor to the bottom of the beam, so the pier would be 81.5" with the planned 2x12x12 on top

The pink lines on the girder are where the upstairs wall is. I added the plumb lines when we moved in this last November.

oh'mike 09-01-2011 03:56 PM

It looks like the girder is rolling a bit----You are right to be concerned.

There are some good structural folks here---let's keep this at the top until one of them checks in---Mike----

Daniel Holzman 09-01-2011 06:09 PM

The post appears to be a home made project. The metal cap is thin, and is not distributing load evenly, as you already figured out. The base is similarly undersized, I wonder if the post is sitting on a home made footing as well. Austin has areas of expansive clay soil, and a steel post needs to have a footing that carries down to stable soil. Unfortunately, there is no way to tell from the photos what the condition of the footer is, but if it is comparable in design and construction to the post, it could well be inadequate.

My recommendation would be to temporarily support the beam using screw jacks specifically rated for temporary support (DO NOT USE hydraulic car jacks, they lose pressure over time), or use temporary cribbing to support the beam after you jack it up. Remove the existing post, install a properly designed footing (your building inspector may be able to help with the footing design), and install a new, rated column adequate for the load (you are going to have to compute the load on the jack based on the geometry of your house and the code based per square foot loads for the tributary area).

Make sure the column you use (often called a lally column) is rated for long term support. The column can be fabricated to proper length by a supplier, and should come with a heavy steel plate at the top. Typically there is a steel plate at the bottom as well. The steel plate at the bottom is attached to the footer using J bolts or similar, and the steel plate at the top is attached to the beam using lag bolts. I wouldn't use brick to support the column, although you could if you like the look, to me it is more work. If you do use brick, you still need a proper footer, and the detail for the connection at the top is a little trickier, you still want a positive connection to keep the beam from moving around on the beam.

shadetree 09-02-2011 12:21 AM

Thanks a ton for the detailed reply!

I can almost guarantee that there is no special footing other than the slab under the post currently. The post itself was originally about 2 feet from where it is now, and judging by the other entry-level mistakes the builder made (like no collar ties on the rafters, inappropriate notching, lack of soffit vents) I'm sure proper footings were also an oversight. Fortunately, I'm on the top of a small hill and the limestone bedrock is only about 4-6 below ground level where my house is, so I'm not terribly worried about harming the 12 slab.

However, I'm not opposed to doing this project right, could a proper footing be built on top of & attached to the slab? Or would I need to cut through the slab to get to the bedrock below? I don't think I can get equipment to cut though the 12+ of cement that is there.

Can jack posts be used to lift as well? I was planning to use a bottle jack to raise the beam up and the jack posts to support it afterward because I wasn't aware that you could lift with just the jack-posts.

And brick pillar would indeed be acceptable to support the girder in this situation? Or would it only be acceptable to support the column? I was kinda confused by the 2nd to last sentence of your post.

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