New column footing right next to and partially supported off of existing masonry wall footing

[DCStructures]

I'm sizing a footing for a new steel column located next to an existing masonry basement wall. The new column needs to be as close to existing wall as possible (allowing space for base plate). Foundation of existing masonry wall is unknown, but assumed to be continuous wall footing made of brick (building dates to early 1900's).

Is it acceptable/common practice in a situation like this to locate column centered on combined area of new column ftg and existing bearing wall ftg, and design new ftg area for concentric loading? Because with the column located so close to the existing wall it's technically not centered on new footing. But if I look at new ftg independently with column located eccentrically, then bearing pressure is way too high. How is this situation typically handled. I'm sure I'm not the first person to deal with this....

Any other tips for dealing with construction of new foundation adjacent to an existing masonry wall/foundation? Is there any reason I'd need to underpin? New footing will be same depth or shallower than existing; we don't want to undermine the existing footing.

Would you dowel into existing ftg and roughen surface where pouring new concrete? Can this be done if existing footing really turns out to be brick as assumed?

 

[mtu1972]

I would never do what you are describing, because I would not be sure of all of the existing loads on existing masonry wall. Nor would I want to be responsible for that footing.

Look up pump-handle footing or foundation, or strap footing.

Your new column will be supported off the end of a grade or strap beam that is supported off of two footings. One is adjacent to the existing wall foundation and the other is 1 bay back into your building. The grade beam cantilevers over the one footing to support the column, so the load on that footing is magnified by the beam's cantilever action, but can be designed for a uniform bearing pressure.

You may also find this in some old textbooks.

gjc

 

[hokie66]

Agree with mtu1972 that your proposed solution doesn't work. You can't expect to combine a new footing with an existing brick footing, and dowels wouldn't help. His suggested way of using a strap beam is one way. Another would be to demolish enough of the existing brick to get your new concrete footing in.

 

[civeng80]

Keep the footings separate.

Any reason why you want to keep the steel column close (hard up) to existing brick wall?
Is it because you want to use the existing wall as a party wall?
Separating the footings will also eliminate any Title issues.

Solutions for eccentric footings.

Use strap beams to tie pad to other footings and/or use piles (bored piles) and pile cap to eliminate rotation of the pad.

 

[DCStructures]

Good thinking, all. Strap footing seems like excellent solution. Any good recommendations for online resources for design of strap footings.

Civeng70- column close to existing wall is architectural requirement.

 

[civeng80]

Don't know of online references.

But "Joe Bowles Foundation analysis and design" is an excellent reference for strap footings.

 

[FixedEarth]

This is from at least 10 years ago.

http://www.soilstructure.com/

 

[DCStructures]

FixedEarth- thanks!

 

[FixedEarth]

Here is the solved example. It references Bowles.

http://www.soilstructure.com/

 

[a2mfk]

Consider a micropile such as a helical auger. They can be installed through holes as small as 3" diameter and can give you some impressive bearing capacity depending on your geology. They can be installed using small-ish equipment (depends on the contractor) such as track-mounted machines about the size of a big lawn tractor, and can be installed adjacent to walls.