If anyone is interested in this.

I decided that I should locate the support at the corner of the chimney and use a PT 2x6 as an anti-buckle beam for the PT 2x8 that is acting as the support post. I don't trust a few Tapcons to provide the pullout strength to prevent buckling, and I don't want to be liable for a piece of the house dropping 7/8" in a split scond.

By the way, I measured the actual deflection yesterday = 7/8" in 15 feet span. This is a doubled 2x8 joist. That's old rough sawn 2x8s which are really their nominal dimensions. A main point load is right above the place where I'll put the column - midspan.

A picture being worth 1000 words:

 

what is making the double 2x8 sag so much in the first place? do you thing transforming a chimney into a column is a good idea?

 

He's not transforming the chimney into a column, he's using the footing for a column pad and using the chimney as a sway brace for the column. With the 2x6/2x8 post you're creating I can't see any appreciable loads transferred to the chimney.

As you said, Karma, be delicate and watch what is going on as you lift it, those old 2x8's might not want to straighten out.

 

oh ok, I didn't quite get that from the orginal posts but now I understand...good idea

 

instead of using a 2x6, what about a larger madeup piece of beam such a LVL 14 7/8". The wider width may help keep the wood from torquing which could happen based on the load being placed at an end point rather then centered in the beam carrying it to the footer.

 

Thanks for the review, reveivl. I will go slow, like you say, 1/4" per day over 3 days and keep an eye to what's going on.

72chevy, I don't really follow what you're saying about why it would torque - I feel that a 2x6 No1 SYP on edge provides enough deflection resistance to prevent a 7' column from buckling under the point load. I guess I could try to estimate the point load and do an anti-buckling calculation, or I could replace the 2x6 with a 2x8 for more strength, but not sure it's really necessary. You can be sure I will lag the 2x6 to the column like there's no tomorrow.

 

sorry, I misunderstood the function of the 2x6. Sounds like you may have already begun the work, but I've run across old chimney stacks where they've poured additional concrete around the chimney base to cover the settling from many years previous-in which case it would be more difficult to determine if its a footing or just a 4" slab.

Thanks for sharing the idea-I'm going to file this one away :thumbsup:

 

Update:

For anyone who is in a similar situation - be careful that you actually have a footing close to the chimney.

I probed down with a masonry bit 12" and I found out the so-called "slab" was only 2" of soft concrete and then nothing but sandy soil.

Needless to say I won't be setting a column right there. Good thing I checked it before setting it. I can picture the crunch and crackle that I would have heard, and the creaking house settling down again.

So... make no assumptions about footings, is the moral of the story.

Many thanks to Skymaster who emphasized the need to check the footing in this thread I posted under 'construction'.

Anyway, I think the chimney just goes down below the 'slab' with bricks. I can't be sure because I only drilled a 5/8" hole with a masonry bit and angled it in various directions to probe. Sandy soil everywhere except the same plane as the chimney sides - and somehow it felt like brick to me touching the bit, so I think they laid the chimney starting below the basement floor grade.

Does anyone know about historic methods of footing chimneys?

 

Here's a pic. Depth of concrete is marked with the blue tape on the rod.

 

Good prelim Karma. Saved yourself on that one. Whats next?

 

If it were my house, I'd pour a pad and set the post. But I think this client wants to live with the sagging joist, cut off the bottom of the door above, so it will close, and go ahead sheetrocking the basement ceiling with the sag.

That's the difference between some clients and me.

 

Ive had a similar problem. I talked the HO into letting me dig a footer with spud bar and post hole diggers. Jacked it up slow and 6X6. But it was a change order. Your HO sounds content with the sag huh?

 

Well, he's cost-conscious. I'll talk to him tomorrow and make sure he doesn't want to correct the condition rather than try to cover the symptoms.

 

You should never attach anything to a masonry chimney, even a new one, unless it is for the purpose of bracing it laterally.

 

Thanks for the advice. That was my initial mistake. The second solution - a built-up T-section post - doesn't bear on the chimney at all.

But what kind of footing would you form to bear a point-load that is completely eccentric, i.e. loaded on one edge of the footing. Or would it be an L-shaped footing extending around the corner of the chimney, with adequate depth to spread the load around, and laid with a rebar mesh - essentially making a rectangular footing with the load in the center, only it's missing one quadrant where the chimney is.

 

Sort of like this is what I am thinking:

 

Is it really not possible to move the post away from the chimney?

 

Yes, it is an issue of corridor width. With this configuration, we have exactly 36".

 

You can't move the post away from the chimney along the corridor wall?

 

Hi Mighty Anvil. You're right, it would not be in the way of the corridor, but it would still be in the way of the intended floor plan, and also the center of the sagging beam (its lowest point) is right there at the corner of thchimney. Maybe I could come 3-4 inches out in front of the chimney and put in a traditional lally column. How does this look in terms of getting adequate footing?

 

To me a foot would be the minimum and 18" even better. The beam span can be effectively relieved an any point beyond the 1/3 span point on either side (or both). Once the span has been reduced by a third or more the exsiting beam strength should be more than adequate. If you intend to lift the sag, lifting at 2 feet off the center point one or both sides should still work. Design a good structure and then design the room around it. Restrictive conditions like this can often lead to great designs if you give it a chance.

Don't let the new footing touch the chimney or it's footing and don't undermine the existing soil under the chimney. Assume the soil under it is bearing at a 45 degree angle and don't break that plane within 6 or 8" of the chimney. The most important goal is to prevent the chimney from moving later and having to be rebuilt at high cost. Carefully protect what you have. The chimney is a booby-trap waiting for you to get sloppy.

Alternatively, if layout is important, jack up the beam (or level the floor above) and add one or two LVL's full span. Bolt the new to the old.

 

as long as your new footing and chimney footing are at the same elevation, (do not dig deeper than the chimney footing or place the new footing at a higher elevation) you will not cause the chimney to settle. An eccentric loading can be handle by using a larger footing. Also what are you soil conditions? Like I said in my other post, you need to estimate the loading your new column will have on it.

 

MA brought up a good point of not letting the new peir pad touch the chimney or it's footing. Would 2" foam around the chimney and footing work when poured for the new. Then dig out the foam and use a 2" expansion joint?

 

Thanks, Mighty Anvil, Chompie, and JustAFramer. This forum is the best. I hope I am not using it too much.

I understand the point about not disturbing the chimney's existing stability, and also that it's not necessary to relieve the beam so close to the midpoint. I did intend to separate any new footing from the chimney - probably by a foam separator like JustAFramer said. I also was going to be sure not to dig any deeper than the exisitng chimney's foot. Except it's unknown conditions down there - I think the chimney extends down with brick but that's just from probing with a hammer drill. I'm not even sure about that.

Good point about interesting designs growing from structural limitations. If it were my home, I would place a column about 12 to 18 from the chimney and make that the end of a little sidewall to a storage area with shelving. But this client tends to be pretty stuck upon his own designs.

I've already refused to build a stair balustrade for him because he had wide gaps of 10" in the thing. I told him the code dictates 4" max openings and that's with good reason for child safety, so he said he understood if I feel I can't build it - but didn't change the design to my suggestion. That's the kind of client he is. Really nice guy, but stuck on his designs.

 

Is there a way to dig a new footing right next to the chimney and set a 3.5" lally on it? I assume you are framing around the chimney and brace anyway, so maybe you could bury the column in the framing?

Just a thought. I'm glad I don't have to jack up that double... That's a lot of deflection to counteract. I can hear the snap, crackle and pop from here!


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That's what I get for posting without reading the whole thread. That was a waste of 5 minutes, huh?

 

Karma-

Sounds like you figured it out. Eccentric loading on a foundation as you have sketched would be minor if you have sufficient depth to the new footing. You may want to consider extending your new footing under the existing chimney stack. Epoxy some steel from the chimney foundation to the new foundation. I would imagine that the 2" slab is a lip around the chimney and not the entire chimney foundation.

I always tell my clients to go upstairs and figure out the reason for the sagging. Check the upper level walls and attic for point loads inadvertenly placed on interior non-bearing walls. It is much easier to relocate a roof strut than it is to dig up under a house and place a footing.

Best of luck..

Engineering Guru