Freestanding wall with footing on one side only 1

[PSEPK]

Hi, All!

I have to design a brick masonry freestanding wall, with footing on one side only.
The wall will be 15 ft high, above ground level. RC columns shall be provided tentatively at 10 ft on centers, within the wall.

Wind load is to be as per ASCE 7-05 category C, for 100 mph wind. design is to follow US codes.

I want to have some guidance on how to go about it? and, to know about preferable options. Link to some relevant example or sharing of experience by those who already have done something similar, would be appreciated.

Thanks.

 

[KootK]

Fun.

1) So does the brick span horizontally to the concrete columns?

2) Watch P-delta effects under deflection. Just the self weight of the wall can cause problems. I've had this come up when looking at free-standing CMU fire walls.

3) Pay lots of attention to your concrete detailing at the opening/closing joint between your concrete columns and the footing. Bad things can happen at those free edges.

4) When you get settlement, it's probably not going to be uniform. It will cause the wall to tilt some . It's probably not a big deal but should be considered.

5) Will you locate the footing deep for frost protection? If not, and the wall is long, consider breaking it up into discrete lengths. Frost lenses can develop somewhat locally and cause differential heave along the length of long things.

6) Would a brick faced concrete or CMU wall be more economical? I assume that there's some reason, other than elegance and fearlessness, that's leading you to go all brick.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[BAretired]

Is the wall on a property line?

Wind blowing toward the footing side is easily handled. Wind blowing away from the footing side requires enough dead weight to balance the wind moment with an appropriate safety factor. This means a rather inefficient foundation design. Alternatively, you could use drilled piles to resist the moment.

BA

 

[msquared48]

The maximum allowable soil stress will likely govern the design of the footing.

Mike McCann, PE, SE (WA)

 

[PSEPK]

Thanks for your responses.

KootK!

Yes, the brickwork span horizontally to the concrete columns.

Burnt clay brick masonry is cheaper in my current project area. RC columns are for strengthening the brick wall.

BA!

Yes, the wall is on a property line. And, the main reason to go for one-sided footing.


BTW... How do you people design freestanding walls? Using spreadsheets, or some other software?

 

[dcarr82775]

Just good ol' spreadsheets and handcalcs.

 

[SlideRuleEra]

Interesting problem. There is a way design a footing that will apply uniform pressure to the soil and, simultaneously, lower the unit contact pressure with the soil. Take a look at a 10' long section of wall, with the RC column in the center. Treat the load from this section of wall as one of the two loads on a classic "combined footing". The second load is the dead weight of the footing. By properly proportioning the thickness and dimensions of the combined footing, you can get a uniform soil bearing pressure. Wind load will make the soil pressure non-uniform, and that should be checked, but the wind load is very short term.

Somewhat of an "outside-the-box" look at the problem since it results in a "saw-tooth" plan view of the footing... but it will work, should prevent differential settlement, is reasonably constructible.

See the attached sketch.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[KootK]

Brilliant SlideRule. That little trick is going in the vault.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[BAretired]

But the centroid of the sawtooth footing is eccentric to the combined weight of the wall and footing, so there will be differential pressure under dead load alone. I don't think that can be avoided.

BA

 

[SlideRuleEra]

BA - You are right. After seeing your post, I rechecked my numbers. Compared to a rectangular footing, a similar size trapezoid shaped footing can reduce eccentricity but not eliminate it. Will take more than manipulation of footing geometry to solve this.

KootK - I suppose you had better remove my original claims from the vault... or at least put an asterisk by it that it can help, but not answer the eccentricity problem.

In the meantime, I'll see if my wife has cooked a "humble pie" for the holidays, so I can have a slice.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[BAretired]

Forget the "humble pie", SlideRuleEra. Have a slice of turkey instead.

BA

 

[spats]

Is there any way to get them to move the wall a little bit? Even 6" would help a bunch.

 

[SlideRuleEra]

BA - Think, I'll do that, sounds a lot more tasty.

http://www.SlideRuleEra.net

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[PSEPK]

Thanks a lot respected fellows, especially SRE and BA, for your valuable analysis and opinions.

spats!

Do you have some other idea, in case wall is moved by 6"? I am interested to know that.

 

[KootK]

@Sliderule: you still get some points for out of the box thinking.

@OP: the extra six inches that Spats mentioned will accomplish at least two useful things:

1) It'll improve the peak soil stresses at the edge.

2) It will facilitate better rebar detailing at that all important opening and closing joint (my point #3 above).




The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[BAretired]

In typical Alberta clays, I would probably use piles and grade beams. If piles are not an option, then the best solution is to use a strip footing wide enough to carry the dead load of the wall, coupled with outrigger grade beams at each column with a small counterweight footing at the end to take care of the moment due to wind and eccentricity. The length of the outrigger is optional but would likely be substantial in order to resist wind pressure on a 15' high wall.

BA

 

[KootK]

Piles would address a lot of the concerns mentioned here.

@BA: if the numbers supported it, would you be comfortable with a single line of piles and grade beams beneath the wall? Or would you still want to see outrigger/roll beams? If the outrigger beams were themselves tied down with piles or ground anchors, they could be fairly short.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[BAretired]

@KootK,
I would be comfortable with a single row of piles, but I am guessing that the pile diameter would be greater than the wall thickness, so it would be offset from the centroid of the wall columns; nevertheless, if the pile is big enough, it should be okay.

BA

 

[SlideRuleEra]

If the piling were driven to cantilevered 15' out of the ground, spaced at 10' intervals, they could replace the current columns. The brick infill could be supported by a concrete beam going from pile to pile. Then the pile perform triple duty:
1. They are "dressed up" to cosmetically look like columns.
2. They are the wall's foundation.
3. They resist the wind load force.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[KootK]

That would be slick. Maybe the columns could be cast in an "H" shape so that the brick walls could key into them. I've seen highway sound barriers constructed in a similar fashion using precast columns and block.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.