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Old 01-12-2013, 12:15 PM   #16
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The Lally column was invented by John Lally, and has been manufactured by Dean Column since 1929. The original Lally column was a concrete filled tin plate tube, and has been improved and standardized since then. Dean Column currently uses 16 gauge steel tubing, and makes the column in either a 3-1/2 inch OD or 4" OD model. They use 3000 psi concrete to fill the tube.

The concrete provide most of the compressive strength of the column. For example, the 3-1/2 inch column has a net area of 9.6 square inches, of which about 9 square inches is concrete. At 3000 psi, the concrete would have a net compressive strength of about 27,000 lbs. The ultimate load capacity for a 6 foot long 3-1/2 inch diameter column is listed in the Dean website as 31,000 lbs, so you can see that most of the load is carried by the concrete.

As the column gets longer, buckling begins to control, and the allowable load decreases rapidly. For example, the same column in a 12 foot model has an ultimate load capacity of 16,400 lbs. Computing the buckling load on a composite steel/concrete structure is complicated, so it is fortunate that Dean has done the hard mathematics and published their table.

The concrete is claimed to provide greater resistance to fire than a hollow steel column of equivalent vertical load capacity, however there is no documentation offered in the Dean Column website. It is certainly true that steel weakens greatly when subject to heat, so the claim may well be true. In residential settings, a fire sufficiently hot to weaken steel in the basement would likely burn the house down completely, and there may be little advantage in having columns survive such an inferno. In industrial settings, there may be great advantage in having fire resistant construction, so there a concrete filled column may be important.

In any case, Dean Column makes their columns filled with concrete, and I believe they have very competitive pricing, since concrete is relatively inexpensive compared with steel, and their use of concrete allows them to use thin steel versus the required gage of their competitors.

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Old 01-12-2013, 01:23 PM   #17
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Originally Posted by itsreallyconc View Post
jo, we also use adjustables but i'd always thought the main reason for conc filling the steel columns was fire resistance as steel bends & collapses when exposed to hi heat,,, conc allows the steel to resist more the hot effects... isn't the main support still the screw on top of the column ?
I'm not talking about concrete "inside" of the steel column, but concrete around the bottom to lock the post in place both vertically & horizontally. The protocol here is to always place the screw at the bottom, encased in concrete. All adjustment should be made to the column before the floor is poured (or "diamonds" are left out around the columns, and patched in after the stucture is built) and if the columns would need to be adjusted later, the pad is probably failing anyways...........
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Old 01-12-2013, 03:49 PM   #18
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thought we were talking retrofit - i give up nevertheless, thanks guys - jo & dan
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Old 01-28-2013, 12:34 PM   #19
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I realize this is an old thread I started, however when pouring the concrete do I want to add "bolts" or anchors for the lally column? Or will this be adjusted afterwords?
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Old 01-28-2013, 12:48 PM   #20
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I realize this is an old thread I started, however when pouring the concrete do I want to add "bolts" or anchors for the lally column? Or will this be adjusted afterwords?
What did your engineer call for? You can embed anchors or drill in expansion anchors afterwards.
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Old 01-28-2013, 01:00 PM   #21
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Engineer did not specify. Also, he did not specify any rebar either. I was planning on just drilling afterwords but I am wondering which would be "easier" for a DIY'er. In addition, this is getting inspected so it obviously has to be code compliant.

If the engineer did not call for steel, would I be incorrect in adding some (in the inspectors eyes)?

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Old 01-28-2013, 01:12 PM   #22
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No. But if the engineer signed and sealed a plan without rebar and without anchor bolt specifications, I'd be calling that engineer and asking him/her what you should do. I find it hard to believe that a PE would put years and years of blood, sweat, and tears on the line by not covering all of their bases. Engineers just don't leave things to interpretation.
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Old 01-28-2013, 01:13 PM   #23
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You can add steel, but since the footing itself is 12" thick, it will not see any bending and all stresses are from shear radiating out (45 degrees downward) from the footprint of a base plate so a unreinforced "chuck" of concrete will be adequate.

If you want to feel "warm and fuzzy", throw in some steel and jump through the hoops of supporting it and placing the concrete properly with the steel in the way.

You never know what mood an inspector is in and how much time he has to spend, since most communities do not make a penny on inspections concerning the time and paper work for problems that require even more work.

Dick

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Old 01-28-2013, 01:17 PM   #24
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90%+ of the 24" x 24" x 12" post pads we pour do not receive rebar, for the reason Dick stated above.

As for anchors, "if" installed the way I mentioned before (the pad is finished 3-4" below the floor, and a floor cap is poured AFTER the column is set) there is no need for anchors at the base.........

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