Knee Brace from Column to Footing 2

Even with a knee brace, the force will still go straight down.

On top of that, footings are complicated to reinforce and usually don’t work like people hope they do.

Thanks a lot JLNJ for sharing your views, that's what I also interpret for load transfer.
But the client engineer ask me to give reasoning why the load won't transfer through the knee brace..
Could you help me for that?
Would like other members to share their thoughts too..

Are you an engineer?

Or better yet is the "client engineer" an engineer??


But I'll choose to give a slightly more helpful response. This is fairly basic engineering, but I managed to come out the otherside of an engineering degree not knowing plenty of basic stuff, but thoroughly about to follow a code recipe book. So I won't hold it against you.

Try googling "stiffness attracts force". This is just a starting point.

Now if you were very adept you might be able to transfer the load to an offset foundation. I can think of a couple approaches (depending on the details of the structure) but all are quite convoluted and would certainly involve more than just a knee brace.

Do not mean to insult. But neither of you should take on the job, for one offered a non-solution, and the other couldn't provide reason for his objection/doubt. However, if the concern was horizontal load, then the story could change. Still not a good idea though.

If you have room to expand the footing out, is there room to expand the column out? You could play with the idea of turning it into a "laced column" (do a quick google search). That will be significantly stiffer than just a knee brace and will be more likely to move the load over and give you a more concentric load on the expanded foundation.

You'll still have some issues to consider, though, and you'll want to work with a geotech. The new soil is probably not compacted/consolidated. So you're going to have uneven bearing resistance. The soil under the existing footing has consolidated over time with the building sitting on it, so just as a stiffer structural member attracts the load so will the stiffer soil. That soil will have to consolidate further (causing settlement in your new foundation) to "engage" the soil under the new part of the footing. A geotech can give you recommendations on reducing this problem.

Have you considered helical piers?

Consider the point where the top of the kneebrace meets the column. For there to be any force in the kneebrace, there needs to be something to resist the horizontal component of the brace force. Since there is nothing to resist this force, there can be no force in the kneebrace.

This is one of most simple and basic principles in the Universe - Newton’s Third Law. Forces follow Newton’s Laws, not arrows drawn on the paper.

Ask the client's engineer to get Ra for the support system shown below (hint: ΣM_B = 0).

OP said:

But the client engineer ask me to give reasoning why the load won't transfer through the knee brace..mad Could you help me for that?

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I feel that the key to understanding this situation, and explaining it to your client, lies in recognizing that this solution could be made to work with the right combination of parameters. It's just that that combination of parameters is likely to be extreme, costly, and spatially intrusive. Consider the following ways that one might arrange things to make this work:

1) You could have the brace tie in at the floor or roof above above.

2) You could make the column massively stiff.

3) You could accept a non-uniform soil bearing stress.

4) You could have a super low soil modulus. You don't want this, though, so we'll not discuss it further.

And definitely be mindful of the warnings that others here have provided about the settlement that would be require to engage the footing extensions, even if those extensions were concentric. In addition to the settlement required to engage the extensions, some of your settlement will also be baked into the cake by virtue of the load in place at the time the footing extensions are constructed. You might actually be able to use this aspect of things to your advantage. If your client were able to accept 2" of settlement instead of 1" of settlement, perhaps no footing remediation would be required. This strategy, of course, requires input from both your geotechnical engineer and your client.

retired13, I will not take it as an insult. I know that I do not have much behavioral understanding due to our teaching approaches back in university(I do not hold them responsible too as it was my duty to learn and ask things at that time). Still, I always try to learn and understand new things as much as I can. I really do appreciate your response.
JLNJ, thanks again for your response.
human909, thank you, will surely check.
phameng, great suggestion.
MI engineer, nope.
Kootk, always great to see how you try to help everyone with your outstanding knowledge. Your comment almost clears all my questions actually. Thanks a lot.

Kootk,
There are some more limitations to the problem.
As per the image shown, they just want to extend the footing on one side(red line). Also, there is plot limit and they can't extend their footing more than 400mm from that(black line).

Sounds like you may need to go back to MI Engineer's suggestion. If you don't have room to add enough concrete to balance it out, you'll need piles. Helicals (or a comparable solution that's locally available) will probably be the best choice.

So you have an eccentric footing to start with (column adjacent to/against the property line). If you can transfer some load to the new post as shown by KootK, depending on the amount load, even extend the footing on one side maybe just worked out. You can estimate the bearing capacity using existing configuration, then use it to design the new extended foundation. Also, instead of the kicker, I prefer the footing in a truncate trapezoidal shape to spread the load more evenly to the ground, provides that lateral load is not a major concern.

I may not have fully appreciated the original condition here. I had assumed that it was a column bearing on a concentrically placed footing. Was the original column placed at the edge of the original footing to begin with? What rectified the eccentricity in that condition? What kind of column are we talking about here? Steel? Concrete? Wood?

Surprise, yes. But KootK your proposed solution would still work for this case.

Kootk said:

I may not have fully appreciated the original condition here. I had assumed that it was a column bearing on a concentrically placed footing. Was the original column placed at the edge of the original footing to begin with? What rectified the eccentricity in that condition? What kind of column are we talking about here? Steel? Concrete? Wood?

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I am sorry that I couldn't explain my situation fully. Attaching a picture with a hand sketch again for understanding.

retired13 said:

So you have an eccentric footing to start with (column adjacent to/against the property line). If you can transfer some load to the new post as shown by KootK, depending on the amount load, even extend the footing on one side maybe just worked out. You can estimate the bearing capacity using existing configuration, then use it to design the new extended foundation. Also, instead of the kicker, I prefer the footing in a truncate trapezoidal shape to spread the load more evenly to the ground, provides that lateral load is not a major concern.

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Nope, the old footing is an concentric one. The allowed limit to extend the footing beyond the plot line is 400mm on roadside(which has already been reached). However, the client says that he will get some sort of special permission from the authorities for more extension if the design is feasible.

Kootk said:

What kind of column are we talking about here? Steel? Concrete? Wood?

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Columns are concrete columns, the whole structure is RCC.