×
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

Jobs

Enlarging an existing column footing
2

Enlarging an existing column footing

Enlarging an existing column footing

(OP)
Does anyone know of a calculation procedure for enlarging an existing column footing due to additional loading? At the interface of the new concrete where bars embed in to the existing footing, there should be a calculation to determine the bars size and spacing based on the new loading. I've never encountered this situation.

RE: Enlarging an existing column footing

If the existing footing has sufficient reinforcing to accommodate the new moment, it's a matter of securing a 'ring' of concrete around the footing or on opposite sides.  The existing footing has to be capable of supporting the new load.  It may be a matter of providing temporary support and casting a new footing edge (or complete) beneath the existing footing.

Dik

RE: Enlarging an existing column footing

You're trying to widen the footing?  It'd probably calculate the reaction pressure from the ground, figure out the load on the new footing area and then dowel in bars to transfer load via shear friction into the existing footing.  This is probably pretty easy if the footings are exposed or could easily be exposed.

It might be better though if you could attach a beam or something to the bottom/edge of the column that would then spread the load into the current footing and new footing from the top.  Then you don't necessarily have to connect the footings into one integral unit.  

Just an idea.  I've never done this, personally.

RE: Enlarging an existing column footing

My first step is usually to contact a geotekkie to see if the allowable soil loads can be marginally increased... if this fails, then look at alternatives...

dik

RE: Enlarging an existing column footing

TLHS that approach neglects the added moment and shear on the existing footing.

If the original footing has shear capacity you will likely have to extend dowels far enough into the existing footing to resist the moment.

RE: Enlarging an existing column footing

Wouldn't you have to jack up the existing footing to relieve the existing stresses? What if the existing footing is heavily stressed; the extension will be unstressed at construction before loading while the existing portion is already stressed. How do you deal with that?

Just thinking out loud -- never worked on something like that before...

RE: Enlarging an existing column footing

The problems with the "donut" approach have been identified above.  If dik's approach to the geotech doesn't work, look at building a new footing rather than trying to glue onto an existing.  

RE: Enlarging an existing column footing

I think the real answer is "it depends..."

RE: Enlarging an existing column footing

The problem here is that the maximum moment that the rebar is resisting is at the column, away from the edge of the footing.  If you increase the moment, then the area of that steel which is very hard to access must be increased - generally not possible unless you drill all the way through the footing.

So do what dik and Hokie said instead.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: Enlarging an existing column footing

In many cases, minimum steel requirements govered the original footing sizes. When this is the case, adding onto a footing is generally not a problem- but you still need to check your moment and shear.

Use TLHS's procedure. I normally add dowels top and bottom for an added comfort level. You will need to widen the footing by at least two feet so they have room to drill the holes for the dowels.  

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!


Resources