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Old 12-13-2008, 10:26 AM   #1
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Lally Column Question


I am tiling my basement floor. I have lally columns that I will not be boxing in. I removed the steel plate at the bottom so the tile could go right up to the column (I shimmed the top with steel to compensate for the thickness). My thinking is the tile will prevent any lateral movement of the column (not that the contractor secured the plate to the floor!).

A friend who is a contractor told me I should not have done this but could not give me a good reason except "they're supposed to be there". Is it OK?

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Old 12-13-2008, 10:48 AM   #2
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Nope, not a good idea. Your friend is right.

Lets say your basement floor concrete is 4000psi mix. Lets say the lally column is supporting 6000 pounds of load (could be lots more, or less). The plate you removed was probably 9 square inches, which spread that 6000 pounds out over 9 square inches of concrete, yielding a 666 psi load. Now you're concentrating the load either on the threads or around the circumference of the pipe column itself (depending on configuration)...So, that 6000 pounds is concentrated in a couple square inches of concrete that may not be able to take it long term. You've also modified a product that is made to work a certain way, and that is never a good idea when you're dealing with loads.

If you're going to the trouble to tile your basement floor, why not go to the additional effort to dress that column up with a wood or sheetrock column wrap. It is easy to do, even for a DIYer without much experience.
That way you could un-modify your modification!

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Old 12-13-2008, 10:51 AM   #3
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Thanks for the advice. I will put them back.
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Old 12-13-2008, 10:56 AM   #4
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Smart move.
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Old 12-13-2008, 11:02 AM   #5
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Originally Posted by Gmartin View Post
A friend who is a contractor told me I should not have done this but could not give me a good reason except "they're supposed to be there". Is it OK?
Your friend is totally correct.

I will tell you the reason.

It has to do with weight distribution. With the plate removed there is a lot more pressure on a smaller area and it could break the concrete over time.

Consider this. The post is hollow and if it is 1/4 inch think and is 4 inches square then you have all the weight on 4 sq inches. With a 6x6 plate the weight is distributed over 36 sq inches which is 1/9 of the weight per square inch.

If you have 10 tons on this post then the weight is 2.5 tons per sq in and should be 1/4 ton per square inch.

The concrete you have the post on is only so thick and can only handle so much weight per square inch.

The plate is meant to distribute the weight over a much larger area.

I would immediately, meaning today, replace the plate before the house settles and you have to jack it up to get the plate back in.

For future reference I would ask questions before making structural changes. I have seen to many home modifications go bad after a few years because these questions were not asked. The bill for fixing it was a steep price for education in the School of Hard Knocks.
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Old 12-13-2008, 11:05 AM   #6
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Nope, not a good idea. Your friend is right.

Lets say your basement floor concrete is 4000psi mix. Lets say the lally column is supporting 6000 pounds of load (could be lots more, or less). The plate you removed was probably 9 square inches, which spread that 6000 pounds out over 9 square inches of concrete, yielding a 666 psi load. Now you're concentrating the load either on the threads or around the circumference of the pipe column itself (depending on configuration)...So, that 6000 pounds is concentrated in a couple square inches of concrete that may not be able to take it long term. You've also modified a product that is made to work a certain way, and that is never a good idea when you're dealing with loads.

If you're going to the trouble to tile your basement floor, why not go to the additional effort to dress that column up with a wood or sheetrock column wrap. It is easy to do, even for a DIYer without much experience.
That way you could un-modify your modification!
See my post. The weight per square inch on your calculations assumes that it is a sold post and I have never seen a solid one.
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Old 12-13-2008, 11:07 AM   #7
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I would also think if the column bottom has any imperfections in it the bottom plate would make up the difference, steel will not crack like concrete will.
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Old 12-13-2008, 05:22 PM   #8
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Marvin:
Concept is right, math a little off:

"Consider this. The post is hollow and if it is 1/4 inch think and is 4 inches square then you have all the weight on 4 sq inches. With a 6x6 plate the weight is distributed over 36 sq inches which is 1/9 of the weight per square inch.
If you have 10 tons on this post then the weight is 2.5 tons per sq in and should be 1/4 ton per square inch."

New math:
Assuming the post is square (likely tubular), 1/4" x 4"=1 sq. in, not 4 sq. in.
10,000 lbs divided by 1 sq. in = 10,000lbs/sq. in
So, his situation is much worse that you calculated.

If round column, with 4" OD, 1/4" thick walls= 6 sq. in; 10,000/6= 1,666 lbs/sq. in.

With the 6" plate, 10,000/36=278 lbs/sq. in.

Somewhere in the above is an answer to a question.
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Old 12-13-2008, 05:57 PM   #9
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Originally Posted by Marvin Gardens View Post
See my post. The weight per square inch on your calculations assumes that it is a sold post and I have never seen a solid one.
My math does not assume a solid post, and that's because they don't make them (that I've ever seen). Lally columns have a tubular post with a threaded bottom cap with receives a threaded adjustment rod, which has a plate of steel (about 3"x3") that bears on the floor. If you re-read my post, you'll see that I mentioned the plate that the OP removed.

You essentially re-stated my explanation in your post, so you must not have read mine thoroughly.
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Old 12-13-2008, 06:00 PM   #10
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Originally Posted by bob22 View Post
Marvin:
Concept is right, math a little off:

"Consider this. The post is hollow and if it is 1/4 inch think and is 4 inches square then you have all the weight on 4 sq inches. With a 6x6 plate the weight is distributed over 36 sq inches which is 1/9 of the weight per square inch.
If you have 10 tons on this post then the weight is 2.5 tons per sq in and should be 1/4 ton per square inch."

New math:
Assuming the post is square (likely tubular), 1/4" x 4"=1 sq. in, not 4 sq. in.
10,000 lbs divided by 1 sq. in = 10,000lbs/sq. in
So, his situation is much worse that you calculated.

If round column, with 4" OD, 1/4" thick walls= 6 sq. in; 10,000/6= 1,666 lbs/sq. in.

With the 6" plate, 10,000/36=278 lbs/sq. in.

Somewhere in the above is an answer to a question.
B
Thanks for the correction. It was before my morning methylxanthine fix (caffeine) and I don't think so well without it. That is my excuse and I am sticking to it...

The bottom line is that there is a whole lot of weight that needs to be transferred over a larger area.

And my guess is that 10 tons is conservative in the weight estimate.
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Old 12-13-2008, 08:52 PM   #11
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Every Lally column I have seen or used here in NJ are SOLID. The steel is a hollow tube but ALL are filled with concrete. We use a big pipe cutter to cut the outer steel and then whack em with a lump hammer to break the concrete fill. Solid is the code here.
I am really curious how he pulled those plates????? That means there was no load on em if he could pull em out; scary thought it is
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Old 12-13-2008, 08:56 PM   #12
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Every Lally column I have seen or used here in NJ are SOLID. The steel is a hollow tube but ALL are filled with concrete. We use a big pipe cutter to cut the outer steel and then whack em with a lump hammer to break the concrete fill. Solid is the code here.
I am really curious how he pulled those plates????? That means there was no load on em if he could pull em out; scary thought it is
Just another thought; a seperate footing is required for each column and they set the columns BEFORE they pour the floor. The Column is set in the floor.
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Old 12-13-2008, 10:18 PM   #13
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... they set the columns BEFORE they pour the floor. The Column is set in the floor.
Just went through this over the summer in NY.

Used 4" columns and cut them the same way you described, then chipped alittle of the concrete out of the center so the metal would sit flush on the plates.

I used two for a basement and asked the inspector if he cared which way i did it (floated in floor around them or lagged on top), he said since there was no garage door he didn't care but said it would be best to lay them right on the footer and have the floor poured around them.
Maybe this is different local to local, he said if the basement had a garage door that they would have to be layed on footing and floor around so if a car bumped into them it would be harder for them to move, but if no vehicles it didn't matter.

I too was wondering how the poster got the plate out.
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Old 12-14-2008, 12:42 AM   #14
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Although it is best to bear the column directly on the pad or pier footing, it isn't completely necessary. Many builders set the pad footing, pour the slab, and then install the column. In my opinion, the better builders block out for the column...They certainly do not have to though.

In garages I require a couple bolts to secure the column to the floor. Code doesn't make that requirement.
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Old 12-14-2008, 01:29 PM   #15
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I am the original "poster". Columns are solid - filled with concrete as described by skymaster. They are round, 4" dia. Of course floor was poured before columns set. I can only assume builder & inspector made sure there are footings under each column.

I used two adjustable temporary columns on either side to raise the beam a fraction to get the bottom plate out. Believe me, there is lots of weight on these columns - it's a two story colonial.

So does the fact that the column is solid change anyone's opinion? If the plate is just to keep the column from moving, my tiling around it will take care of that. Besides, it's in a cellar, not a garage.


Last edited by Gmartin; 12-14-2008 at 01:36 PM.
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