×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Help. Need help with Footing in the wrong location
4

Help. Need help with Footing in the wrong location

Help. Need help with Footing in the wrong location

(OP)
We are the EOR on an office building and we did the stair design also for local fabricator. We located the footing for the single column for the monumental stair. The stair was revised but we didn't catch the revised location for the single column. Well the Architect says we cannot cut the floor. We have a 3'x3' footing with a 4" concrete slab. The new post is 14 1/2" off of the centerline of the footing. Allowable bearing is 2500 psf.

So P/A = 1.53 psf
M/S =3.71
P/A +M/S = 5.24

RE: Help. Need help with Footing in the wrong location

so what exactly is your question???

RE: Help. Need help with Footing in the wrong location

(OP)
I am sorry. The Architect said we cannot cut the floor. Is there a field fix? Over sized baseplate with a rod going back under the stair to take thrust?

RE: Help. Need help with Footing in the wrong location

One thing I'd do is run the problem by the geotechnical engineer and see if there's any extra that be gleaned from the allowable bearing given the circumstances.

RE: Help. Need help with Footing in the wrong location

5.24 psf or ksf?

RE: Help. Need help with Footing in the wrong location

(OP)
5.24 ksf

RE: Help. Need help with Footing in the wrong location

1st thing I'd do is sharpen the pencil and go through my design to make sure I wasn't too conservative with the loads. 1.53 ksf x 3' x 3' = 13,770 lbs - probably mostly live load?

Agree with JStephen, talk to the geotech. If you're using the typical allowable load for the job, its probably based on limiting long term settlements. If you have 10,000 lbs of live load on your stairs long term, I suspect you have other problems. Is the footing sitting on native soil, or at a higher elevation maybe on some better prepared sub-base?

Are the stairs fabricated yet? If your post/baseplate can handle some additional load, you could always look at providing a fixed connection to the footing - realistically probably not going to do squat, but theoretically it should counter some of the eccentricity.

RE: Help. Need help with Footing in the wrong location

Unfortunately, the load is outside the kern of the footing, so M/S is much more than 3.71 ksf.

BA

RE: Help. Need help with Footing in the wrong location

If need be and if the soil will take it, some form of injection, such as two-component cements may improve things enough to do the job.

RE: Help. Need help with Footing in the wrong location

I think the Architect is going to have to accept some penetration of the floor slab. Perhaps a small diameter pile could be used to reduce the area to be cut.

Alternatively, perhaps the stair framing could be modified to permit the support to align with the existing footing.

BA

RE: Help. Need help with Footing in the wrong location

It might be cheaper in the long run to redraft all relevant drawings and reimburse the owner / client for all resultant remedial corrective actions / fabrications etc.

RE: Help. Need help with Footing in the wrong location

What is between top of footing and the bottom of floor slab? If compacted fill manybe enlarge column to sit partly on the floor slab. If there is a question still, pump grout under the slab to compact the soil there and put very small lift on the floor slab Then, with enlarged column sufficient puts significant load on the floor slab in the direction of footing larger area. When all is complete take careful elevations and keep records. Later if there is any settlement, the same injection of grout can bring things back to where they started.

RE: Help. Need help with Footing in the wrong location

I agree with BA. Architect is going to have to accept some form of modification to the slab. Maybe a cored hole in slab under or very close to stair column, then install some form of pile through the cored hole.

RE: Help. Need help with Footing in the wrong location

Your actual maximum soil pressure is more like 10 ksf, not 5.24. It's not a simple summation.

RE: Help. Need help with Footing in the wrong location

Agree with JLNJ - I got about 7300 psf with a 14 1/2" eccentricity - assuming a concentrated load of 12.5 kips to get to the 1530 value for P/A.

Check out Eng-Tips Forum's Policies here:
FAQ731-376: Eng-Tips.com Forum Policies

RE: Help. Need help with Footing in the wrong location

I like TEDstruc’s idea. Hide your repair under the column and everyone walks away happy.

RE: Help. Need help with Footing in the wrong location

On the use of piling, consider cutting out a section of the floor at the present column location. Arrange to temporarily holdup the existing column from beyond the cut out floor section. Cut off the bottom of the column if necessary. Use drills and jack hammers to make holes through the existing footing. Drive extendable mini piles through the cored holes and don't stop extending them until a given load can be taken with no noticeable settlement for one hour of load. How to confirm that load capacity can be by several different methods, including a calibrated jack. Then construct a reinforced pile cap in the space created by the sawed slab removal. Use no-shrink grout between existing column and the new pile cap, then release the temporary column supports. Using several mini-piles, a uniform support situation is created for the new pile cap. Under low headroom conditions mini-piles can do wonders. Top of pile cap can be flush with floor grade and finished accordingly. Of course modifications of this idea are possible, but due to the goof-up to begin with this had to be done right.

RE: Help. Need help with Footing in the wrong location

Even the installation of a couple of micropiles on either side of the column will require penetration of the floor slab.

Dik

RE: Help. Need help with Footing in the wrong location

Quote (JAE)

Agree with JLNJ - I got about 7300 psf with a 14 1/2" eccentricity
. The loading has to be revisited as well as a discussion with the geotekkie.

you mean you cannot rely on tension? <G>

Dik

RE: Help. Need help with Footing in the wrong location

Has the stair and single column been installed? If so, installing a pile is not feasible in which case, the footing would need to be replaced. If not, the area should be clear for installing a single pile under the column.

BA

RE: Help. Need help with Footing in the wrong location

Question of BA. Just how do you install a single pile under an existing column? Why only one?

RE: Help. Need help with Footing in the wrong location

OG... that's why I was thinking of 2... not so much eccentricity.

Dik

RE: Help. Need help with Footing in the wrong location

dik: Working inside a building presents a bunch of challenges. Even the fixes proposed will be influenced significantly on which one might be best do to that restricted place. In our position, there likely are things we don't know that will control how this goes. A photo or two or plan cross section would help a lot. Maybe get the architect to come up with something besides restrictions.

RE: Help. Need help with Footing in the wrong location

OG: no doubt... there are a couple of contractors in this neighbourhood that install micro piles from within. They have a little tripod rig that as long as there is a 3'x7' door, they can install them... not in a crawlspace, though.

Dik

RE: Help. Need help with Footing in the wrong location

Quote (oldestguy)

Question of BA. Just how do you install a single pile under an existing column? Why only one?

If the column is existing, you can't. I am hoping that the column and stair are not in place yet. Then one pile would be centered under the column prior to placing the column.

BA

RE: Help. Need help with Footing in the wrong location

4
I saw nothing in berniedog's posts to indicate that the column was already there. So I think the single pile solution is the least intrusive option. But then, I vote for digging out the footing, casting a new larger footing, leaving enough room in the hole for the architect.

RE: Help. Need help with Footing in the wrong location

Changing the focus from footing level to the top of column level. Is there any way the column load can be picked up within the floor system above and supported by a transfer beam? One end of the transfer beam would be located above the centre of the existing footing, then the other end of the transfer beam could possibly be supported on the perimeter foundation wall. I don't know the layout of the staircase, so quite possibly this might be a conflict. Just trying to think outside the box.

RE: Help. Need help with Footing in the wrong location

Quote (hokie)

leaving enough room in the hole for the architect
another star... great comment... have to be careful with organic material and concrete <G>

Dik

RE: Help. Need help with Footing in the wrong location

Maybe I am missing something, if the slab cannot be cut, then its in place. Thus the column must be bearing on top of the slab? Can the slab take the load, spread out over a bigger area?

RE: Help. Need help with Footing in the wrong location

jrisebo,
Yes, the slab is in place. If the column has not been erected, it is not bearing on top of the slab. It seems unlikely that the slab could take the load unless it was designed to do so.

BA

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

White Paper - PLM and ERP: Their Respective Roles in Modern Manufacturing
Leading manufacturers are aligning their people, processes, and tools from initial product ideation through to field service. They do so by providing access to product and enterprise data in the context of each person’s domain expertise. However, it can be complicated and costly to unite engineering with the factory and supply chain. Download Now
White Paper - Medical Device Design Control
Medical device product development is a highly integrated and regulated process. Implementation of a requirements tracking solution requires attention to a variety of nuanced topics. When presented with the task of tracking the many concept relationships in a project of this type, the initial software solution of choice tends to be a two-dimensional text systems. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close