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Screwed up!


Les
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Anyone out there got any theories regarding how you place steel jackscrew posts? Screw on the bottom or screw on the top? What is the common practice in your area? Inspector lore in my area says "screw on the top when going from concrete to steel and screw on bottom when going from concrete to wood." This is assuming placement after floor is poured and there are adequate footings. I know the "code" but what is the practice?

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Let's just suppose I have an aging victorian that needs some quick support at the interior wall; beam is cracked. Put in a spread footing then I want to use a single tube screwjack. Which way would you put the treads? I am curious because I've heard 9,836 opinions. Well, maybe 10-12.

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Yesterday's Inspection:

200592616225_P6240012.jpg

According to the research of Arlene Puentes, (a friend and colleague from Kingston, NY) it doesn’t matter.

She also notes that the height adjusting screw must be disabled after installation by encasing in concrete, welding or destroying the threads. www.octoberhome.com/draft/adjustcolumn.html

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If you can read the instructions on the label without standing on your head, it's installed right, as a temporary means of support only, not meant as a permanent means of support.

Follow the manufacturer's instructions is the best bet.

Arlene's research says it doesn't matter up or down because they're not supposed to be used as permanent support at all. Not that it doesn't matter period.

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Here is the thing - tens of thousands of houses in my area have them. Vast majority are single type and most are within concrete. Arlene's article is right on point, except in the real world there are building officials that seem to think they are right and there does not seem to be any agreement within their ranks.

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In my part of the woods, I see them. Generally I call them out. Temporary jack posts are just that.Temporary! Some times I see them shoring up a sloppy staircut in older houses. Most of the munis will not allow them. A competant professional general contractor would know that these jack posts are inferior to properly installed "lally columns". Weekend Contractor Stuff.[:-banghea

Jack Ahern Needham on the Charles

Bridgton,Maine

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This was the situation that started all my questions. There are six post in this new house. Four like the photo and two with screw at top. All support steel beam that is midpoint in tji's on approx 30' spans. No footings on any, screw end plates not secured, all had layers of dirt, all threads are lubricated for ease of adjustment, none are plumb, three are supporting their own weight only, etc.. Local municipal building official specified them.

I been doing this for a long time and have become an arogant SOB, but on this job I had a little doubt creep in because none of this made any sense (common). Thought I would ask my partners in crime what they routinely comment on.

During legal cases I have heard reasoning from; screw at top, screw at bottom, no screw, lube screw end to prevent torque, thread load, thread load after welding or breaking and bending, effect of concrete on un-protected metal, fasteners too close to edge of wood beam, size and type of fasteners, footings type and size, "push vs pull" argument, how does encasement in concrete change point load, etc.. I am sure we can come up with many more questions in a free for all discussion.

Like Scott P said "Never really thought of it"

Thanks for the comments!

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The point load at the base will be huge after those plates rust out and they will. If it's a typical basement with 3500 psi concrete (or less) the point loads from the screw could exceed the capacity of the concrete to support the post. Once the post has moved down at all, the loads on the adjacent posts just became 50% greater, and in some cases the load would be doubled.

Another thing: The photo that the Honorable Kibbel posted is of a two piece adjustable post. That post really is for temporary use and I've never seen one rated at more than 2500 lb capacity. They're junk.

The posts that are one piece, are available in 6 inch increments with the screw making the difference between the sizes. The better ones in 4 inch are rated for 12,000 lbs. I lifted a 1600 sq ft ranch with two beams, 2 jacks and 6 of those posts and installed a new basement under the house. There was other bracing, but the posts supported the weight of the structure for the five days of demo and rebuild.

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  • 1 month later...

Getting back to this for a sec guys.

Does anyone have a link or a copy of the installation instructions, from the manufacture or an engineer, for a column? This would be for a typical basement installation.

There is the screw type with the metal pegs for adjustment and the cement filled style. I could use both please.

I have Googled till my computer was blue in the screen but no luck.

Thanks.

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