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.

 

[hokie66]

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.

 

[Eng9876]

@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-concrete-formwork-for.html

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.

 

[hokie66]

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.

 

[Eng9876]

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.

 

[Archie264]

.

 

[Eng9876]

@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.

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

 

[structSU10]

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...

 

[Ussuri]

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

 

[Archie264]

>>>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.

 

[Wallache]

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

 

[Eng9876]

@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.

 

[Eng9876]

@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).

 

[Wallache]

That article is most definitely not American.

 

[Eng9876]

@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.

 

[Ussuri]

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?cmd=display&id=1025

 

[Eng9876]

@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.

 

[Ingenuity]

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

 

[Eng9876]

@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.

 

[JAE]

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:
faq731-376