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Wall and Column Kickers - Why (Pros and Cons)
2

Wall and Column Kickers - Why (Pros and Cons)

Wall and Column Kickers - Why (Pros and Cons)

(OP)
This is a new thread based on this one that was closed. I felt that the answers given were not complete http://www.eng-tips.com/viewthread.cfm?qid=209154#...

Kickers aren't being used so much in construction today, a lot of new construction engineers are learning methods that can be more risky whereas taking a little extra time and setting a template (kicker) against each column/wall can pay back in dividends when saving re-work.

I was recently involved in a project with over 300 columns (using mainly unskilled labour in the middle east), with not one single cover or steel/column alignment issue, how many people can say that?

Why?... we used kickers.

What are kickers?:
A kicker is a small concrete plinth 50-150mm (2"-6") in height placed around a column base in order for you to quickly start your next stage column pour - it sets out the alignment pre-pour rather than post-pour (because if you need to move things, you can do it there and then). It is usually cast with the floor, pad or raft foundation. Construction can be fiddly/slows concreting for the first stage foundation slightly, but lost time is usually made up in time at the column/wall erection stage (if you have crews that know what they are doing).

Having a kicker you can physically see what's not right both in terms of cover and by looking along the kicker bases gives a quick visual indication of what needs to be moved. Obviously your surveyor would set-up a local grid to set these things out. It is easier to look along a straight edge of columns than it is a long string line with wavy 32mm reinforcement starter bars (which are usually placed where they can due to base steel configuration).


The reason why we have column and wall kickers are as follows:

From Checking Engineers Perspective:
For Having a Kicker - Pro's:
1, You can see any column or wall alignment issues immediately, fix any grid problems straight away(Once the concrete is cast and steel alignment problems exist, you don't have to cut the steel, just move it before you pour).
2. Makes the next stage construction (columns and walls) much faster as you only have to butt up your formwork against the kicker (alignment is already done).
3. Gives additional level(concrete elevation) guides as well as screed rails therefore providing better elevation control.
4. Reduces the amount of joints in the concrete. (you only have one joint where a second stage kicker would give you two. - NOT GOOD!)

For having a kicker - Cons:
1. Slower (INITIAL) stage pouring, but less risky. Slightly more fiddly initial construction for carpenters - this is however made up for at the next stage of construction.
2. Has to be done right - a finishing team must know what they are doing, if they mess up, concrete re-work will slow progress down. (use experienced concrete finishers - which you would do anyway).


From the contractors Perspective:

For not having a kicker - Pros:
1. Faster (INITIAL)construction, but risky. (however, many contractors cast a kicker at the second stage but this increases the number of joints in the concrete WHICH IS NOT GOOD). you will lose this time easily with all the re-work.

For not having a Kicker - Cons:
1. Any mistakes in the steel reinforcement could prove costly, whole gridlines in the wrong location may involve structural engineering to fix.
2. Cover issues may need re-work.
3. Increases the amount of joints in the concrete.
4. Once the concrete is poured and has set, mistakes require costly rework and potential structural engineering.

It is always best to have a kicker, you can see any alignment or cover issues straight away and fix them. Any time lost through making kickers is always made up at the next stage. You simply butt up your formwork against the kicker and plumb down for verticality. (don't forget your top column alignment.)

Not having a kicker is risky, best to take your time and get it right. Don't use inexperienced crews for concrete finishing, this is an added risk (and re-work) factor you don't need.

RE: Wall and Column Kickers - Why (Pros and Cons)

I can see the benefit of a "kicker" in setting formwork for the next level, but only if the kicker is in the right place, which I suspect would often not be the case. I have never in 40 years of practice seen a column "kicker" used, and the only place I have used or seen used a wall kicker is where a central waterstop is required.

RE: Wall and Column Kickers - Why (Pros and Cons)

(OP)
@hockie66.

Below is a pic to show you one being used so you can now say you have seen them being used.

I


Here is also another one for you! http://www.acivilengineer.com/2013/03/how-to-make-...

The above is just pros and cons. It is well known that contractors will avoid them if they can but to be honest, the advantages of having them far outweigh the disadvantages.

RE: Wall and Column Kickers - Why (Pros and Cons)

Well, I'm not too old to learn, but your photo is a new one on me. I have only practiced in the US and Australia, so that limits my knowledge of how it is done in other parts of the world. While we are at it with my education, what are those tubes on top of the mat? Aids for screeding, perhaps? Another thing I have not seen.

RE: Wall and Column Kickers - Why (Pros and Cons)

(OP)
The tubes around the column are just polythene in order to reduce the concrete slurrey (cleaning afterwards). You have to remove this before the concrete sets once the kicker is poured and finished. The steel tubes are to assist for screeding (simple straight scaffold tubes).

We have saved a lot of re-work just by having kickers, I always ask for them now.

RE: Wall and Column Kickers - Why (Pros and Cons)

.

RE: Wall and Column Kickers - Why (Pros and Cons)

(OP)
@Archie264.

the thread was about the pros and cons of using kickers, feel welcome to add if you have anything to contribute regarding that.

To me, and this may be a local or national exception, a diagonal brace is usually called either a diagonal brace, (strut or tie, (tension or compression members)), a kicker is something completely different. A kicker is a small concrete plinth set in place for the reasons mentioned above. Working abroad in many countries with many languages, myself a kicker is exactly that. I can appreciate you may have the term used for other things.

It seems that in this instance, even hockie66 learnt something new, which I am glad about, and why I felt the need to share. smile

If you take a look at the link in the above post you can see a finished kicker for a column.

RE: Wall and Column Kickers - Why (Pros and Cons)

Note I have nothing to add about kickers as I am also an uneducated American, BUT -

What country are you from? Basically from Archie and Hokie you can see this is not typical, or really used at all, in the US or Australia. Engineering terminology is different all over the world so your comment about being 'completely wrong' about Archie's kicker statement is only in context to what a kicker is in your country. Maybe you can learn something yourself - us Americans have no clue what the 'kicker' you are talking about is, and to us a kicker is a type of diagonal brace.

I also find your statement about arrogance to be quite ironic...

RE: Wall and Column Kickers - Why (Pros and Cons)

Hokie66, you are correct. The tubes laid across the top mat are screeding rails. At least that is what I know them as.

RE: Wall and Column Kickers - Why (Pros and Cons)

>>>the thread was about the pros and cons of using kickers, feel welcome to add if you have anything to contribute regarding that.<<<

Alright then, here's my contribution: if you have to resort to plinths at the base of your formwork to keep the concrete from flowing out then perhaps the mix is too soupy. And while that might prevent honeycombing it might also lead to over-consolidation or be indicative of too lean a mix or of even of the truck driver putting the hose into the concrete mixer. That said, perhaps imperfect concrete is preferable to honeycombing. Or, if the industry is trending towards highly flowable, pumpable mixes then so be it. Perhaps that will prove to be a good thing.

RE: Wall and Column Kickers - Why (Pros and Cons)

I have not encountered "kickers" on any project I have done in the US. Seems like a solution looking for a problem.

RE: Wall and Column Kickers - Why (Pros and Cons)

(OP)
@Archie264,

The plinth is there mainly for alignment of the columns and something to butt the formwork against. It's very quick to use a plumb bob to get the verticality of the formwork thereafter.

It's not about the concrete mix, consistency or leakage.

RE: Wall and Column Kickers - Why (Pros and Cons)

(OP)
@wallache the link above from civil engineer (under the pic) is presumed an American article, simply by the units of measurement.

However I would sayuntil you see it work, you will adopt this way for sure. Google concrete wall or column kicker to get an idea.

I've worked on many large concrete projects, usually people from different nationalities are absolutely familiar with the method (but not all).

RE: Wall and Column Kickers - Why (Pros and Cons)

That article is most definitely not American.

RE: Wall and Column Kickers - Why (Pros and Cons)

(OP)
@kootk

I am surprised the number of guys that have never heard of them.

1, too many joints is at structural problem, especially within the tension zone(cold joints?)
2. The slab and kicker is monolithic.
3. See below basic textbook. This is a conventional method of construction.

RE: Wall and Column Kickers - Why (Pros and Cons)

Another country perspective from the UK. We used to always use kickers, but some years ago there was a push to move to kickerless construction, primarily because it is quicker and cheaper. A lot of the formwork companies had their own proprietary systems for kickerless construction techniques.

I have not worked in traditional building now for 15 years or so, so I cant say whether kickerless has become the norm. I suspect UK practice would be a mixture of both.

http://www.concrete.org.uk/fingertips-nuggets.asp?...


RE: Wall and Column Kickers - Why (Pros and Cons)

(OP)
@ussuri

Good Post! Absolutely correct.

Contractors pushed to avoid it because it's fiddly, they would rather slow at the second stage, getting credit for the first rather than install them, but it has more advantages than disadvantages. Re-work avoidance being the main one.

The thread is purely about the pros and cons only continuing from another thread.

I would appreciate it if people gave the first post above a good read, then comment if they have more pros and cons for the interest in learning.

RE: Wall and Column Kickers - Why (Pros and Cons)

Seriously, why not reduce the bum-loads of rebar and use PT!



RE: Wall and Column Kickers - Why (Pros and Cons)

(OP)
@Inginuity
This was design by an American using your ACI 318 Structural Concrete design codes.

@kootk

Cold joints are a problem. You would want to minimise the number if you can.

I would disagree with you about the structural aspect, if you have a joint, its a point of weakness, yes there are one at the top and bottom, but you wouldn't want anymore than that if you could help it.

Dowels in reinforced concrete? I am not sure why you would want to drill into reinforced concrete to dowel after you have just poured it? You would want to avoid that too!

Finishes: I'm not sure what you mean. If you mean the joint finish between the kicker and column it's easy same as you would any construction joint.

Gutter berg press? No it's a text book from Chudley (Construction Technology) a widely used book I had years ago.

RE: Wall and Column Kickers - Why (Pros and Cons)

I don't have the 40 years of hokie but about 36 yrs. here in the U.S.
Have done thousands of sf of concrete construction and never have I seen or heard of "kickers" in this context.

Cold joints in columns don't affect structural performance at all.
There is usually adequate steel to prohibit shear issues.
And no axial or flexural behavior is affected.

The linked article is not from the U.S.

Where contractors place joints (at least in the US) is not usually dictated by engineers but the contractors are typically required to submit a joint plan for their concrete placement sequences.

It seems that all of the OP's pros and cons deal more with the ease of construction, the tolerance obtained, and speed of construction....all of which are more concerns of the contractor rather than the engineer.

Check out Eng-Tips Forum's Policies here:
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RE: Wall and Column Kickers - Why (Pros and Cons)

(OP)
@JAE,

Last sentence. This is right, the thread is about the pros and cons from the perspective of both the checking engineer and contractor.

If you haven't seen them I'm surprised. But now you have.

RE: Wall and Column Kickers - Why (Pros and Cons)

I'm not sure why you are surprised. Construction methods vary all over the world.

Check out Eng-Tips Forum's Policies here:
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RE: Wall and Column Kickers - Why (Pros and Cons)

(OP)
@JAE,

I am, and I agree, I have heard of all the methods mentioned, but few have heard of this.

Even the UK, another English speaking country, with differing methods of construction have heard of it. It's good to know what others are doing in the interest of progression in the industry.

Back to the main thread please.

I would appreciate less:

Cold joint issues
X years of experience issues
I haven't seen it issues
Or any other issues other than the first post please.

Appreciated smile

RE: Wall and Column Kickers - Why (Pros and Cons)

What happens when the specified concrete strength of columns exceeds that of the floor?

BA

RE: Wall and Column Kickers - Why (Pros and Cons)

BA's question is quite valid, Considering column and slab concrete are typically of different strengths, and you're going to pour your kicker (chalk me up as another person who has never heard of this word used in this context) and slab at the same time with the same concrete. Then you have a strength discontinuity when you have say 35 MPA column concrete sitting on a 25MPA slab/kicker. How do you deal with that?

RE: Wall and Column Kickers - Why (Pros and Cons)

OK then: There are no engineering pros to the kickers.
They add nothing to the structural integrity, safety or performance of the columns.

They may help the contractor keep his columns straight on in the correct position (maybe)
They may help the contractor avoid concrete leakage around the base of the forms
They may help the contractor avoid lack of rebar cover.
etc.

But these issues have never been a problem in any of the projects I've worked on with good quality contractors.

And BAretired's question is valid - there are many times that the column strength is different (higher) so this is a valid concern.



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RE: Wall and Column Kickers - Why (Pros and Cons)

Normally in a highrise building, the concrete strength for columns has a higher strength than that of the floors. Most design codes recognize that f'c in the floor can be less than f'c in the column because the floor concrete is laterally confined and hence capable of resisting higher stress; nevertheless, codes have certain limitations on acceptable strength differences. If the "kicker" is cast with the same strength concrete as the floor, it is not confined and will be over-stressed unless provisions are made to strengthen it. Adding high strength concrete in the kickers is possible but is not a reliable solution as it could be easily missed on site.

That would be one of the Cons that I see to the "kicker" concept.

BA

RE: Wall and Column Kickers - Why (Pros and Cons)

(OP)
@BA,

Good point, and one to note! (Thumbs up!) in this instance the concrete is all the same (5550psi) or C38.

RE: Wall and Column Kickers - Why (Pros and Cons)

Just curious, and sorry for violating your rules. Why did you respond to "@kootk"-twice? I can't see his input in this thread. Was it deleted?

RE: Wall and Column Kickers - Why (Pros and Cons)

@Hokie: I withdrew my contributions here as a protest of sorts. I objected to what I perceived as the shabby treatment of my colleagues here. I also objected on behalf of my "retarded" aunt who has been sending me the same meticulously wrapped life savers booklet for Chistmas every year since I've had teeth. I kept it polite but probably exceeded the limits of site-appropriate discourse.

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: Wall and Column Kickers - Why (Pros and Cons)

Right. I will just have to use my imagination. Thanks. I was wondering, because usually when posts are deleted, there is at least a line showing there was something there. Maybe not when you delete your own post...

RE: Wall and Column Kickers - Why (Pros and Cons)

Well, I'd meant for my protest to be visible. I announced my departure and blacked out all of my prior comments with black highlighting (I thought that was pretty clever). I assume that it was a moderator that actually made my posts disappear in earnest.

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: Wall and Column Kickers - Why (Pros and Cons)

There is no actual moderator until someone reading the thread red-flags it. You would have to guess who dobbed you in.

RE: Wall and Column Kickers - Why (Pros and Cons)

Minor tiff, but you did miss that Koot is a metallica fan.

RE: Wall and Column Kickers - Why (Pros and Cons)

Kootk getting special privileges when he deletes! Deserving i suppose bow bowleft
The all black text makes more sense now knowing the music taste!

So i think there is no engineering benefit to the means and methods proposed for the raised curb.

RE: Wall and Column Kickers - Why (Pros and Cons)

Kickers were absolutely standard practice in bridge work in the UK when I worked there (up to early 80's), and were widely used in Australia in the 80's, but much less widely used now. I don't know what normal practice is in building work, but I suspect that they are not used much in Australia.

Like Eng9876 I think they have much to commend them, and would like to hear from people who still use them, or who have stopped using them for good reasons.

Comments along the lines of: we don't use them in the USA, so they must be a waste of time, are not very helpful, to be polite.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Wall and Column Kickers - Why (Pros and Cons)

I've seen kickers of sorts used in the states, but not for the reasons described above. The only time I've seen them used was for walls as part of tunnel form construction. Providing a little starter curb gives the tunnel forms something to run along. Easier to get the forms set that way. Have not seen this in conventionally formed structures.

RE: Wall and Column Kickers - Why (Pros and Cons)

MrHershey,
In tunnel construction, or any underground construction, you would generally have waterstops. The kickers provide for setting of the waterstops, and the slab reinforcement is not compromised.

RE: Wall and Column Kickers - Why (Pros and Cons)

'Tunnel form' construction, not tunnel construction. The structures I am referencing are above ground (though I suppose you may be able to use the system below ground as well).

Sample photo from Google images, not mine:


RE: Wall and Column Kickers - Why (Pros and Cons)

"Tunnel form", that's another term I was unaware of. A formwork system, and one aim seems to be to cast the walls and slab concurrently. That I don't want to happen on my jobs.

RE: Wall and Column Kickers - Why (Pros and Cons)

I'll bite. Why would you not want to do that on your jobs?

They actually make structures work a lot easier on the design side because you're forced by the tunnel system to have walls at a maximum of about 15' on center. Slab deflection is practically nothing with relatively little reinforcement for spans that small, wall stresses are extremely low because you've got so many of them. Can get by with relatively minimal reinforcement for low- and mid-rise buildings. Not sure what there is not to like from a structural standpoint.

Goes up extremely quickly as well.

RE: Wall and Column Kickers - Why (Pros and Cons)

I think I know why hokie66 doesn't want it on his jobs. Pouring walls and slabs together creates gaps in the walls due to concrete settlement while curing.

BA

RE: Wall and Column Kickers - Why (Pros and Cons)

When you cast the wall and slab together, the top of the wall is subject to plastic settlement cracking. The form supports the slab, while the concrete in the wall continues to settle a bit. Those plastic cracks can be closed by revibration, but when speed is the overriding principle, I would think the revibration may be overlooked. This is the reason you don't cast columns with the supported floor.

RE: Wall and Column Kickers - Why (Pros and Cons)

Understand what you're getting at, but this formwork system has been in use around the world for over thirty years now (Concrete Construction Article from 1982 on vibration of concrete in tunnel forms). To my knowledge, have never seen any issues reported with monolithic pours of walls/slabs in tunnel forms. Keep in mind the pour occurs at the exact same time, this isn't pour your walls in the morning and slabs in the afternoon. Usually the wall/slab mix is the same and poured during the same continuous pour. Proper consolidation is of course important as it is with any other job. Fortunately tunnel forms are rather specialized so the contractors who use them tend to know them well and know what they need to do to produce a quality building. All of our tunnel form jobs have been with the same contractor because they're the only ones in the area with the forms to do it. Speed is always a driving factor with every job. With tunnel forms what we've seen is the formwork provides the speed. There's not as much pressure on the contractors to skimp on the consolidation, inspection, and QC because they're already moving much quicker than normal with the forms.

But let's assume that we do get settlement cracks at the top of the wall, right underneath slab soffit. Would tend to think these would be horizontal cracks. Once you remove the formwork wouldn't the cracks close up on their own as the weight of the slab goes in to the wall? At that point would it really behave any different than the construction joint (really just an intentional crack) you'd get between slab and wall anyways?

RE: Wall and Column Kickers - Why (Pros and Cons)

Quote (BARetired)

I think I know why hokie66 doesn't want it on his jobs. Pouring walls and slabs together creates gaps in the walls due to concrete settlement while curing.

@hokie: a few weeks ago, I read an excellent AU document on plastic settlement cracking that you referred me to. Based on my read of that document, the expected problem here would be slab cracking adjacent to the wall rather than gap formation at the slab/wall joint. Can you confirm that? Ditto for you BA if you have personal experience with this.

@MrHershy: with these buildings, what is the lateral system perpendicular to the tunnels?

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: Wall and Column Kickers - Why (Pros and Cons)

Tunnels go in both direction. Just turn them 90 degrees and you've got shear walls in both directions.

Another example from Google image search, not mine:

RE: Wall and Column Kickers - Why (Pros and Cons)

KootK,
The plastic settlement cracking can be either horizontal at the top of the wall, or vertical in the slab adjacent to the wall, both due to continued settlement of the wall concrete after placement and vibrating, while the slab concrete remains supported on the forms. As in all plastic cracks, if you get to them quick enough, you can close them by revibration.

Mr.Hershey,
No, I wouldn't consider a horizontal crack which closes when the forms are removed to be the same as a normal construction joint, which closes in the plastic state of the slab. Pouring "the walls in the morning and slabs in the afternoon" is better practice, but I suppose that is not how this system is intended to be used.

RE: Wall and Column Kickers - Why (Pros and Cons)

KootK,

I have never witnessed the problem because I have never permitted slabs to be poured monolithically with walls or columns. Our code recognizes the problem by increasing required development length of horizontal reinforcement by 30% when it is placed such that more than 300mm (12") of fresh concrete is cast below the reinforcement.

BA

RE: Wall and Column Kickers - Why (Pros and Cons)

BA,

I think that requirement is generally for top steel in deeper beams, and is indeed another example of the adverse affects of plastic settlement. Another example is the reflective cracking over top bars in deep elements like spread footings with top steel.

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