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Footing with cold joint

Footing with cold joint

Footing with cold joint

(OP)


Let's say you have concrete placement done one half of it (see the red lines) and the other top half (or rest of portion) of it placed next day. Can it affect the punching shear strength? How about one way shear strength?

RE: Footing with cold joint

You need to be able to deal with the horizontal shear demand on the cold joint. If that's satisfied then I believe that one way and punching shear should be ok.

If you can penetrate the first pour with an internal vibrator then the concrete should be able to bond as though the two pours were monolithic. If not, you may need to consider bonding agents or rebar dowels across the joint. Depending on the size of the footing etc, it may be cheapest to just rip out the first pour.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Footing with cold joint

(OP)

Quote:

You need to be able to deal with the horizontal shear demand on the cold joint. If that's satisfied then I believe that one way and punching shear should be ok.

If you can penetrate the first pour with an internal vibrator then the concrete should be able to bond as though the two pours were monolithic. If not, you may need to consider bonding agents or rebar dowels across the joint. Depending on the size of the footing etc, it may be cheapest to just rip out the first pour.

1. Should footing and lower part of column be casted monolithic? Or can footing have concrete placement first and then say 5 days later the column would be casted?

2. Let's say you have the footing casted first with dowels or even column bars sticking out already. And say the footing depth is 20 inches. What would happen if the contractor pour the extra concrete they didn't use in other part of building (because the concrete truck has certain volume and sometimes it arrives with more than the requirements and there is extra) into the footing. Instead of the designed 20 inches footing depth.. say it becomes 25 inches.. then after it the column is casted the following week.. would this unintentionally make the 2 way punching shear (and even one day shear) stronger? This happens in construction when they have extra concrete and they can't dump it elsewhere so they add it to the footing or foundation.

Thank you.

RE: Footing with cold joint

You seem to be trying to solve the contractor's problem of ordering the wrong amount of concrete.

For your first question, KootK is correct. For one isolated footing, rip it out and do it again. The horizontal shear issue for a pad footing can be quite severe, and is not easily solved after the first lift hardens.

It is normal to cast footings first, then columns after some time has passed. Casting them together is not only difficult, it can lead to quality issues. And column concrete is often a higher strength grade than the footing.

There is not a problem with casting a footing thicker than designed. But then wouldn't the column starter bars be too short?

RE: Footing with cold joint

1) Columns can, and should, be cast after footings.

2) The footing over pour may well improve shear capacity but it will shorten the lap between your footing dowels and column vertical bars.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Footing with cold joint

(OP)

Quote:

For your first question, KootK is correct. For one isolated footing, rip it out and do it again. The horizontal shear issue for a pad footing can be quite severe, and is not easily solved after the first lift hardens.

Hokie66. Books I read like Design of Concrete Structure 14t Edition doesn't mention this horizontal shear thing in the Footing and Foundation part but only punching shear and 1 way shear. May I know why it's not mentioned and what books mentioned them? Checking 2 other books.. it's not mentioned either. Thank you.

RE: Footing with cold joint

I don't know specifically about that book. Maybe the authors just thought that no one would do such a stupid thing in a footing. But I imagine that your book does address horizontal shear in different contexts. Horizontal shear stress in beams and slabs is typically of lesser magnitude than in a pad footing, because the contact area of the pad joint is less, and the applied pressure is greater.

RE: Footing with cold joint

(OP)

Quote:

It is normal to cast footings first, then columns after some time has passed. Casting them together is not only difficult, it can lead to quality issues. And column concrete is often a higher strength grade than the footing.



The contractor usually casted the footing and lower part of column at same time. The president reasoned it must be monolithic. Also the foundation and column happen to be both 4000 psi so they can be casted monolith (at least the lower part of the column and footing). How can there be quality issues for this?

RE: Footing with cold joint

Who is the "president"? Why would you want to cast the column in two pieces when one will do? The less operations, the better. Or is this again due to concrete ordering issues?

RE: Footing with cold joint

(OP)

Quote:

Who is the "president"? Why would you want to cast the column in two pieces when one will do? The less operations, the better. Or is this again due to concrete ordering issues?

concrete ordering issues.. and the reason for the partial column up to that point is to add a ground beam to it.. so they order a concrete truck that can fill them at same time.. because it's difficult and expensive to order separate truck just for that one meter column height.. the purpose of the ground beam is to make the column more stiff.

the president is owner of the contractor company who follows the structural plans by any methodology he sees fit (that meets the structural company plan criteria like 4000 psi).

RE: Footing with cold joint

I see. Of your practices, the worst one would be casting a footing in two lifts, one one day and the other the next. That needs to be avoided.

RE: Footing with cold joint

(OP)

Quote:

I don't know specifically about that book. Maybe the authors just thought that no one would do such a stupid thing in a footing. But I imagine that your book does address horizontal shear in different contexts. Horizontal shear stress in beams and slabs is typically of lesser magnitude than in a pad footing, because the contact area of the pad joint is less, and the applied pressure is greater

Does this horizontal shear affect more on 2 way punching shear or 1 way shear? How about for mat and bigger footing? If someone can find any reference about this in foundation section of books and whether it is called by another name, please let me know.. thanks

The contractor told me they did this in other buildings when they ran out of concrete (estimate error of volume) or when the truck broke down. We just ended in arguments because of his stubbornness.

RE: Footing with cold joint

Shear is shear, but horizontal shear is different from either one way or two way shear as you know it. Horizontal shear is on the horizontal plane, and in your case the concern is the along the joint between the two placements. I imagine you know that shear in short, heavily loaded flexural elements typically controls, and a pad footing is a good example of such.

RE: Footing with cold joint

I would say that it does affect two way shear more than one way shear because:

1) Vertical and horizontal shear are complementary.
2) Two-way shear stresses will be much higher than one way.

That said, I'll usually design for the horizontal shear associated with one-way shear only and leave it at that. I do so because I believe that the high localized horizontal shears associated with two-way action can be redistributed laterally.

I believe that the same procedure is applicable to rafts as well.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Footing with cold joint

(OP)
Kootk.. Thanks. I'd like to ask something unrelated. How does building with rocks surrounding the basements perform. Would the rock push against the walls?

RE: Footing with cold joint

Quote (ottles)

would the shorter pink building foundation moves along with the rock underneath it.. or would it slide and crush the wall of the tall building?

It should be designed not to slide along the rock so it shouldn't crush the wall of the tall building.

Quote (ottles)

Won't the rock surrounding the basement of the tall building crush into the tall building wall during seismic activity? Or would the wall and rock move together?

The rock will likely impart its seismic load to the building primarily by pushing against the diaphragm below grade that is closest to the surface. It shouldn't impact the walls themselves much as the walls will be flexible relative to the rock mass. If this were soil instead of rock, however, then you would have to worry about the soil getting seismically thrown against the walls.

Quote (ottles)

Lastly. If you will say wall and rock would move along together. Can the pink short building foundation also move along with the rock due to coefficient of friction making it not able to slide (let's say no key or doweled are installed between the pink building foundation and rock)? What do you think?

Yes. That's just how it ought to be designed in my opinion.

Here's an article that discusses this issue a bit from Los Angeles. And another from the Kiwis.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Footing with cold joint

(OP)

Quote:

The rock will likely impart its seismic load to the building primarily by pushing against the diaphragm below grade that is closest to the surface. It shouldn't impact the walls themselves much as the walls will be flexible relative to the rock mass. If this were soil instead of rock, however, then you would have to worry about the soil getting seismically thrown against the walls.

You mention the walls will be flexible relative to the rock mass. But isn't it the retaining wall is made up of column and beam grid touching the rock. Let's say the rock impart its seismic load to the column-beam joint portion connecting to the diagraphm.. won't the rock crack the column-beam joint?

When you mention walls. Did you mean the concrete that is not part of the column and beams that is external and touching the rock? But wall should also include the external column, beams and column-beam joints. If it's this you were saying.. you mean even column, beams, column-beam joints are flexible relative to the rock mass and rock will not affect/crack these external column,beams?

If you mean the diaphragm as composing of the column,beam, column-beam joint, what would happen to them as the rock push against them? Would the rock crack them? the rock mass is so huge.. could any diaphragm even resist them? Imagine you have a rock in your hands and you hit a wooden toothpick with it.

RE: Footing with cold joint

Quote (ottles)

You mention the walls will be flexible relative to the rock mass. But isn't it the retaining wall is made up of column and beam grid touching the rock. Let's say the rock impart its seismic load to the column-beam joint portion connecting to the diagraphm.. won't the rock crack the column-beam joint?

In my region, it would be walls and slabs below grade at the perimeter rather than beams and columns. No matter though. Columns will also be flexible compared to the rock and your beams should be braced by, and deliver their load to, the diaphragm (slab).

Quote (ottles)

If it's this you were saying.. you mean even column, beams, column-beam joints are flexible relative to the rock mass and rock will not affect/crack these external column,beams?

Yes.

Quote (ottles)

If you mean the diaphragm as composing of the column,beam, column-beam joint, what would happen to them as the rock push against them? Would the rock crack them? the rock mass is so huge.. could any diaphragm even resist them? Imagine you have a rock in your hands and you hit a wooden toothpick with it.

By diaphragm, I'm mean the stuff in the structural floor. Slabs and beams. Not columns. And yes, the diaphragms can take the load. I think that you're getting off track thinking of the basement as a stationary thing that sits still while the rock pounds on it. Instead, imagine your building floating in a bowl of jello. As you shake the jello, two things happen:

1) The jello imparts forces to the basement and;
2) The basement moves around along with the jello.

For the most part, the basement does move along with the earth mass. Never perfectly so however. If it were perfectly so, there would be no seismic force imparted to the building from the earth anywhere other than at the footing to rock interface. And sometimes, we do design buildings assuming that to be the case. But then we also assume that those buildings' height is the the height from the footings to the roof for seismic purposes.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Footing with cold joint

(OP)

Quote:

In my region, it would be walls and slabs below grade at the perimeter rather than beams and columns. No matter though. Columns will also be flexible compared to the rock and your beams should be braced by, and deliver their load to, the diaphragm (slab).

You mean solid concrete wall and slabs in the perimeter? Many buildings have 2 floors of basement parking and I think some use column-beams and hollow blocks (or masonry blocks) at perimeter to make up the walls just like above grade. Are you saying you haven't encountered this in practice and this is not allowed??

Back to the pink short building. If it slides, would it inertia be greater than the rock and break the wall or equal inertia and force? Or would the wall even cushion the sliding of the pink short building foundation (a short period short building)? What is the usual case in practice?

Would a building with pad footings slide more? If one is build right next to a building with 2 basement parkings.. are there guidelines how the foundation should be distance from the adjacent building.. but lets' say it's one meter distance.. it's very big and so much space would be used up and I don't think it's the norm in practice. There are thousands of buildings with pad footings that is touching the adjacent building basement parking wall. Had there reports where the pad footings (or combined footings) shear into the basement parking wall? Thank you.

RE: Footing with cold joint

Quote (ottles)

Are you saying you haven't encountered this in practice and this is not allowed??

No. I'm saying that perimeter beams and columns in the basement wall is not common where I practice. I have seen the system and it is allowed to my knowledge.

Quote (ottles)

Back to the pink short building. If it slides, would it inertia be greater than the rock and break the wall or equal inertia and force? Or would the wall even cushion the sliding of the pink short building foundation (a short period short building)? What is the usual case in practice?

One of two things needs to happen:

1) The short building foundation needs to be designed so as not to slide. This is the usual practice.

2) The basement wall of the main building needs to be designed to restrain the leftwards movement of the short building foundation. I've never heard of this being done and can imagine that it would be difficult to make it work.

Quote (ottles)

Would a building with pad footings slide more?

More than what? I'm not sure what we're comparing pad footings to.

Quote (ottles)

If one is build right next to a building with 2 basement parkings.. are there guidelines how the foundation should be distance from the adjacent building

Sometimes there are legal requirements for spacing based on ownership. It's a weird thing structurally. Even if two basement buildings have some separation, they would still push on one another below grade through the interstitial soil. The soil can, of course, transfer axial loads across the gap. It's much less of an issue with rock of course.

Quote (ottles)

.. but lets' say it's one meter distance.. it's very big and so much space would be used up and I don't think it's the norm in practice.

You're right. It is very common to have adjacent building foundations pretty much in contact with one another.

Quote (ottles)

Had there reports where the pad footings (or combined footings) shear into the basement parking wall?

I've never heard of such a report. Again though, this should be a moot point as the shorter building should be designed not to slide.





I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Footing with cold joint

(OP)

Quote:

More than what? I'm not sure what we're comparing pad footings to.

Smaller spread (or pad) footings should slide more compared to larger combined footings.. larger footings have more surface and hence more coefficient of friction.

Quote:

I've never heard of such a report. Again though, this should be a moot point as the shorter building should be designed not to slide.

But in usual buildings.. the pad or spread footings are not doweled or keyed to the soil or rock underneath.. without these.. most spread footing buildings should slide.. don't they? how do you design them not to slide without using dowel or key to soil/rock?

Also for adjacent structures. of course no problems if both don't have basements. But in practice.. you don't know if your adjacent lot has basement parking.. so I'm asking what are the in field seismic performance where the adjacent building has 2 basement parking and one beside it doesn't have any basement and the designer doesn't know.. so most should slide (especially spread footings without dowel or key).

RE: Footing with cold joint

Quote (ottle)

larger footings have more surface and hence more coefficient of friction.

I disagree. The coefficient of friction has nothing to do with footing size. The frictional force developed is a function of the total weight on the footing of which the footing self weight is only part.

Quote (ottles)

most spread footing buildings should slide.. don't they? how do you design them not to slide without using dowel or key to soil/rock?

I design my buildings not to slide. Sometimes that requires only friction, sometimes it requires the foundations to be keyed into the rock so to speak.

Quote (ottles)

But in practice.. you don't know if your adjacent lot has basement parking..

I do for my buildings. The new foundations need to be coordinated with the positions and other characteristics of the existing foundations.

Quote (ottles)

o I'm asking what are the in field seismic performance where the adjacent building has 2 basement parking and one beside it doesn't have any basement and the designer doesn't know.. so most should slide

I've never seen any reports on that type of seismic performance. And since I don't agree that most buildings should slide, I consider it to be an issue of little relevance to practical design. In my opinion, buildings need to be designed not to slide around unless it's on seismic isolation systems.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Footing with cold joint

(OP)

Quote:

I do for my buildings. The new foundations need to be coordinated with the positions and other characteristics of the existing foundations.

How do you compute whether a building and foundation can slide or not? In your projects.. how many storeys usually before the weight can make it no longer slide? just estimate? can say 6 storey with 2 bays with say 16 feet span still slide or do only 2 storey (2 bay 16 feet span) building slide?

Does soil also make it slide or only rock underneath?

Please see the image below.



Let's not discuss about building with basements anymore.. let's discuss now building that has no basements and the foundations are level with one another. When let's say someone is building a small house (pink one) beside a large building (on left).. what instance when the larger building footing can move the small house footing and shear it to bend the column? The ground accelerate together but the footing is different sizes and inertia.. so when the ground shakes to the left.. either the small house can slide into the big footing and get bent in the process or if the ground shakes to the right and let's say the big building slide (it can shear the footing of the small pink building), right? what other scenerios can happen?

Thanks a lot!

RE: Footing with cold joint

(OP)
1. If ground accelerates in seismic movement, do all structure foundation (whether it is 50 storey trump tower foundation or a one storey poor man foundation) moves the same amount? If yes. Then if there is no slide, then there is no banging of foundation. Right?

2. The equal displacement principle says that a building lateral system will experience approximately the same amount of displacement under design seismic excitation regardless of the level of ductility built into the system. But let's imagine a solid stone that is 2 storey high. Would it even have displacement between the roof and the ground?? How can the equal displacement principle apply in case of the 2 storey high stone?

RE: Footing with cold joint

Quote (OTTLES)

How do you compute whether a building and foundation can slide or not?

You compare the lateral loads to the available lateral resistance at the foundation level. For a shallow foundation building, the resistance is some combination of friction against the earth, which is a function of reliable dead load, and earth pressures against anything that's keyed into the earth.

Quote (ottles)

how many storeys usually before the weight can make it no longer slide? just estimate? can say 6 storey with 2 bays with say 16 feet span still slide or do only 2 storey (2 bay 16 feet span) building slide?

There's no rule of thumb. It has to be determined on a case by case basis depending on how the lateral system is arranged etc. A very expansive and heavy building may still have sliding problems if all of the lateral load is delivered to a few local shear walls or braces and those systems themselves do not collect enough dead load to resist sliding locally.

Quote (ottles)

Does soil also make it slide or only rock underneath?

Both soil and rock can be used to resist sliding. Rock may offer improved possibilities for resisting a lot of force through keying foundations into the earth.

Quote (ottles)

what instance when the larger building footing can move the small house footing and shear it to bend the column?

This shouldn't happen in any instances as both buildings should be designed not to slide. If the buildings were designed such that one was supposed to slide into the other during an earthquake, that would be 1) very complex to design and 2) rather poor practice.

Quote (ottles)

If ground accelerates in seismic movement, do all structure foundation (whether it is 50 storey trump tower foundation or a one storey poor man foundation) moves the same amount?

Yes, and that amount is assumed to be zero. The foundations ride along with the earth and do not move relative to it.

Quote (ottles)

If yes. Then if there is no slide, then there is no banging of foundation. Right?

Right.

Quote (ottles)

Would it even have displacement between the roof and the ground??

Yes. Everything displaces under load. In the case of the two story stone, that displacement would be extremely small.

Quote (ottles)

How can the equal displacement principle apply in case of the 2 storey high stone?

It would apply in exactly the same way so long as:

1) The stone had a yielding mechanism that would kick in prior to reaching the elastic level earthquake load.

2) The stone possessed the ability to strain past yield in a ductile manner.

Of course, neither of those things is likely to be true for a two story rock. It is an interesting thing to consider however.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Footing with cold joint

(OP)

Quote:

It would apply in exactly the same way so long as:

1) The stone had a yielding mechanism that would kick in prior to reaching the elastic level earthquake load.

2) The stone possessed the ability to strain past yield in a ductile manner.

Of course, neither of those things is likely to be true for a two story rock. It is an interesting thing to consider however.

So the equivalent displacement principle is only valid for similar systems. It doesn't work for stone building block vs column-beam based building. But do you think it is still valid for braced frame vs nonbraced frame? The braced frame is very stiff because it is braced. So it can't have equal displacement vs a special moment frame. So it seems the equivalent displacement principle is only valid for ordinary moment frame (not braced) vs intermediate and special moment frame (not braced)? I tried to google this but I can't find the exact statement that it is not valid for braced frame so wanted confirmation from you. Appreciated your invaluable assistance. Thanks!

RE: Footing with cold joint

Quote (ottles)

So the equivalent displacement principle is only valid for similar systems. It doesn't work for stone building block vs column-beam based building.

You misread me. The equal displacement principle does apply to the stone and could be mobilized if the two criterion that I mentioned above were met.

And the principle is very much applicable to properly detailed braced frames. They're stiff and they can be displaced beyond yield without becoming unstable.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Footing with cold joint

(OP)


Quote:

And the principle is very much applicable to properly detailed braced frames. They're stiff and they can be displaced beyond yield without becoming unstable.

The above came from this excellent ref http://www.iitk.ac.in/nicee/IITK-GSDMA/EBB_001_30M...
It's in page 102. There you will see the braced frame has lesser lateral displacement with equivalent lateral energy (say base shear in all cases is 5700 kN). Hence the equivalent displacement principle doesn't seem to work. If you will say when the brace framed building yields.. it has equal displacement as the moment frame on left, but then it will yield at larger seismic energy. Unless you are saying the drawing is not accurate and the braced frame depicted has lesser seismic energy that is why displacement is lesser and if it's equivalent 5700 kN lateral force. The displacement (from roof to ground) is similar??

RE: Footing with cold joint

That is a neat reference. Thanks for sharing it.

I believe that you're misunderstanding an aspect of the equal displacement principle. Nothing about it implies that different structures should have the same displacement. It only says that the different possible load-displacement curves of a single structure tend to have similar maximum displacements. Obviously, a skyscraper and a one story shack are not going to undergo the same displacement during a seismic event.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Footing with cold joint

(OP)

Quote:

That is a neat reference. Thanks for sharing it.

I believe that you're misunderstanding an aspect of the equal displacement principle. Nothing about it implies that different structures should have the same displacement. It only says that the different possible load-displacement curves of a single structure tend to have similar maximum displacements. Obviously, a skyscraper and a one story shack are not going to undergo the same displacement during a seismic event.

In the drawing. Is the first moment frame building and second global braced frame considered a single structure? I think no.

But a building without braced frame and only moment frame. I think ordinary frame and moment moment frame only vary in the ductility and sizes so can they be considered a single structure for purpose of the equivalent displacement principle load displacement curves? Or if you will build a building, would the displacement be the same if its same storey and height and only differs in it being ordinary moment frame or special moment frame?

Of course skyscraper and one storey shack don't have same displacement because of storey shear and storey force but I'm talking about a similar height storey and not braced.

RE: Footing with cold joint

Quote (ottles)

Is the first moment frame building and second global braced frame considered a single structure?

Agreed, different structures.

As for the rest, I disagree strongly. A braced skyscraper can be expected to respond very differently from a moment frame skyscraper. There's a lot more to response than just story height.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Footing with cold joint

ottles,

In the future, when you completely change the subject of a thread, please start a new thread. Keeps things on the site in better order.

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