Jack-post like column

[Robbiee]

Hi all,
The attached is an image of a concrete column in a parking garage that has a steel top like a jack post. Wondering if anyone knows anything about this "jack-post"; properties, why it was used, capacities, ...etc.
Thanks.

 

[jayrod12]

Yikes!

In my mind, that should've been temporary to allow for proper levelling etc, and then the concrete column be poured to the top.

Can the concrete beam above transfer the design load properly to that post? I have my doubts. That's a pretty narrow plate for how wide that band beam is.

 

[dik]

Interesting... how long has it been in place. I'd probably do some sums, checking punching shear.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Robbiee]

Jayrod:
There used to be round columns inside the wall. For some reason, they were removed and replaced with the new square pier and the jack-post.
dik:
We don't know how long they (3 column) have been in place.

 

[jayrod12]

I do not like the look of that. Hard to see in the photo, what kind of connection is there between the jack post and the beam, and the jack post and the column. Really just feels like a stability issue waiting for a bit of off centre loading from the band beam to cause this thing to topple.

 

[bones206]

A gust of wind blew away half of the drawing set during construction?

 

[dik]

As long as it's secured and has capacity, and the slab can take the small area, and there is lateral resistance, I don't see any issues. There are a few 'ands'.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Robbiee]

Currently there are no visible connections between the post and the slab or the pier, and I don't know if there are any embedded ones. But assuming there are none, we are proposing to have it connected.
Now, to know the capacity of the steel post, I was hoping somebody can identify it or have some load tables, else how its capacity can be known? Using sectional area of the pin and conservatively assuming Fy?
Worth noting that we did not see any structural issues in the slab such as cracking or excessive deflection.

 

[jayrod12]

If it were me, I'd likely be forming and pouring concrete around it right to the underside of slab.

 

[dik]

Sure, but may not be necessary...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[jayrod12]

I can't imagine a single engineer looking at that and thinking it's totally fine without looking really hard at a whole bunch of things. It's just not worth the questions everytime someone else looks at it. Why, on a concrete structure would there randomly be 3 adjustable jack posts? With no visible connection to the structure. It just seems hokey.

 

[dik]

I wasn't advocating anything else... if it ain't broken... There's no question that it is unusual, but it may not be deficient.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[canwesteng]

Client is better served with 1500 dollars of concrete than 1500 dollars of engineering. If they are asking you to sign off I'd just make them pour a new post.

 

[Robbiee]

canwesteng,
There are three columns like this one. What 1500 dollars are you talking about? To pour new "posts" we still need to engineer them, apply for permit, hire a contractor who will need to hire a shoring engineer. We also will need to do site visits and provide reports on the construction work. Our estimate for this work will be over $50k.

 

[dik]

For 50K, I'd look at what you have to see if it works... in particular if it's been there for decades.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Robbiee]

dik,
Agree and that is why I came here hoping to see if somebody can identify this screw post.

 

[TLHS]

Are they arranged in a way where they may have been intended to allow for adjustment of the elevation of the slab? Could there have been a previous settlement issue that was expected to be ongoing or something similar?

I doubt it, because you probably would have mentioned some fancy detailing at the connections to the lateral system.

 

[phamENG]

If I may speculate: three columns were damaged somehow, contractor was hired to repair damaged columns, contractor poured little square pedestals and installed temporary jacks, columns were demolished, something happened and the contractor got fired, the garage wasn't collapsing when they left and it "looked okay" so they left it.

You're unlikely to get any sort of capacity for them because they were probably some sort of temporary shoring. They may have even custom fabricated them for the job. Or, in a very unlikely scenario, maybe they were engineered to be permanent and custom fabricated for the purpose. Apart from old lally columns in residential basements, screw jack type columns are usually temporary.

 

[dik]

Is there any sort of identifying name? load capacity? can the original contractor be located to see if he knows? Can you temporary remove one (jacking and shoring) to load test it? or design one to replace it that works (HSS stub with top and bot plates)?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Robbiee]

TLHS:
Only three of many others in the same column line. I don't think that was the reason. Also, the currently owner does not have any records of these posts. I think if elevation adjustment was needed, the current owner would've been told.