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

[Eng9876]

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#post

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.

 

[Eng9876]

@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.

 

[JAE]

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



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[Eng9876]

@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

 

[BAretired]

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

BA

 

[jayrod12]

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?

 

[JAE]

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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[BAretired]

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

 

[Eng9876]

@BA,

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

 

[hokie66]

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?

 

[KootK]

@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.

 

[hokie66]

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...

 

[KootK]

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.

 

[hokie66]

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

 

[Brad805]

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

 

[EngineeringEric]

Kootk getting special privileges when he deletes! Deserving i suppose
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.

 

[IDS]

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/

 

[MrHershey]

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.

 

[hokie66]

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.

 

[MrHershey]

'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:

 

[hokie66]

"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.