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Building Technology
 
Filler slab on RCC columns
Hi everybody,

I intend to cast filler slab supported with RCC columns. Should I take any special precautions on account of roof beams?

Please advise
Manickam Pillai Sivakumar
Responses
 
Filler slab on RCC columns
Hi Manickam,

As per my knowledge, filler slab is as strong as the conventional slab and it's just the replacement of concrete in the tension zone. So, the filler material is not at all a structural part of the slab. That is what my perception is and if there is any wrong in this please correct me. So, structurally you should only beware that some concrete is always there in the tension part of the slab. Also, a lot of know-how is available with COSTFORD people and HUDCO; they may be of help.
Rahul Ravat
Filler slab on RCC columns
Thanks Mr. Ravat. From an aesthetic point of view, is it advisable to plaster the exposed concrete preferably with mix such as plaster of paris etc. Please advise.

Thanks,
Manickam Pillai Sivakumar
Filler slab on RCC columns
I hope you are not asking for structural advice; in that case you should consult an engineer.

The filler material should preferably be lightweight and have a rough texture. This is to ensure strong bonding with the beams. We have had a couple of cases of filler material falling off due to non-bonding with the beam.

Plastering the beams is up to you. Even if you want to leave it exposed, some sort of finishing will be required as cement slurry tends to leak under the filler material resulting in jagged beam edges.

A lot depends on your detailing. If the beams are 'T' shaped and the filler material is resting on the beam, then you need not worry about falling of the filler material. A lot will depend on your specific case- --the spans, the materials and your beam layout.

Hope this helps.
Vishwanath Kashikar
Filler slab on RCC columns
Hi Manickam,

As correctly said by Mr. Vishwanath all depends on how you are doing the detailing. Also, you should consult a structural engineer. About aesthetics, it's everyone's own choice and may defer. One would like to keep it exposed and one may not. But, if you are thinking to keep it open you can just finish as per your choice may be by POP or just can plaster it.
Rahul Ravat
Filler slab on RCC columns
Dear Sivakumar,

Filler slabs on RCC column, I do not understand technically because, filler slabs are made by hand tamping & RCC column is by pin vibrator, hence having a weak roof on strong columns does not gell well with me.

However, aesthetically, it is very nice, you need to just make sure that your filler materials are the size which fit in between your reinforcements after leaving adequate cover. You need to first get the slab designed by a structural engineer as has been adviced in previous posts also. Just request hime to make sure that spacings are comfortable / large enough to fit in filler materials.

VERY IMPORTANT:- You should have a set of very good masons to do the work. Execution is the main issue in filler slab, not so much the design aspect. Your shuttering has to be perfect, so should the tamping be so that the 'filler materials' do not slip away during laying of roof!!!
Chitradeep Sengupta
Filler slab on RCC columns
Sivakumar, BE CAREFUL, ASK AN ENGINEER.
A concrete slab has more steel bars towards the columns than a filler slab. These steel bars are needed, because all the efforts have to get into the column. There is even a danger of punturing the slab (even a concrete slab) depending on the weight of the slab or the overload. If you want to get a filler slab on a column (RC or not) you will have to reinforce it seriously, fore example by having (integrated) concrete beams (instead of fillers) on the axes of the column. It will not be easy to get the joists of the fillerslab and these beams on the same level underneath, as the joists have to fit into the lower steel rods of the beams. I add a schematic sketch of what I mean. But an engineer can tell you more.
Tom Schacher
Filler slab on RCC columns
Sivakumar, BE CAREFUL, ASK AN ENGINEER.

A concrete slab has more steel bars towards the columns than a filler slab. These steel bars are needed, because all the efforts have to get into the column. There is even a danger of puncturing the slab (even a concrete slab) depending on the weight of the slab or the overload.

If you want to get a filler slab on a column (RC or not) you will have to reinforce it seriously, for example by having (integrated) concrete beams (instead of fillers) on the axes of the column. It will not be easy to get the joists of the fillerslab and these beams on the same level underneath, as the joists have to fit into the lower steel rods of the beams. I add a schematic sketch of what I mean. But an engineer can tell you more.
Tom Schacher
Filler slab on RCC columns
Thnaks M/s Rahul Ravat,Vishwanath,Chitradeep and Tom for your responses to my query on filler slab.

Probably it is a mistake on my part that I haven't communicated precisely about my query.

What I intended to ask was whether I can provide the fillers in the slab supported by RCC columns and not exactly over the columns/beams.

Strutural detailing of the slab is over. I have discussed this issue with my structural engineer. He said the filler slab can be provided but with no compromise on thickness of the slab.

But the intension of the filler to reduce the reduntant portion of the concrete.

I am bit confused. I am enclosing herewith the sketch indicating provision of fillers in a concrete slab.

I need your advise on this.
Manickam Pillai Sivakumar
Filler slab on RCC columns
the structural engineer is right. the slab thickness is not reduced by resorting to filler slab technique. by replacing the concrete in tension in the slab with a cheap light weight filler material, you are saving on cost (of concrete-cost of filler material)and weight (weight of concrete-weight of filler material).
while designing a filler slab, you have to collaborate with the structural engineer to determine the spacing between the reinforcement bars. you need minimum cover for all bars on all sides and that will determine the spacing of the filler material. technically speaking (not calculating indeterminacy of structural systems) the filler material is not required and the slab will stand even if you dont fill it up with anything. however, this is not feasible from a construction point of view. in that sense, your filler material is almost like a lost form. (i am saying almost because unlike a lost form, the filler is still contributing to the dead load of the slab).

i presume that the engineer is aware of the dimensions and weight of the filler material. could you tell us what your filler material is? from the sketch it seems as if the filler material will not be visible from the bottom as the bottom profile of the material is a curve. from your sketch i am also assuming that you are plastering the bottom surface of the slab. if such is the case, please remember that the cement slurry might not enter the centre indent completely while casting the slab, so you will be left with an uneven bottom for the slab. eventually you will end up using too much material while plastering the slab. of course all this discussion is redundant if your sketch is not showing the actual profile of the filler material.

i hope this clarifies a few points. if you are still not sure, please talk to someone locally who has done this type of construction.
Vishwanath Kashikar
Filler slab on RCC columns
Hi,

My entire house is cast with Filler slab... there are couple of points we need to take care.... there should not be any filler materials used in shear region, the reinforcement continuous to remain closely spaced.... in regions away from shear regions you can go in for filler slab with reinforcement widely spaced.... generally accepted slab thickness for filler slab is 5 inches, of which filler materials can be planned in non-shear region on for 2" at bottom, minimum of 3" concrete is must above filler material. That is to say filler material can be pots upto 2" deep placed inverted bottom open.... any material like thermocol, computer keyboard etc., can be used as filler material... all those which have some amount of elasticity and are not toally brittle like glass......glass can break during curing process.... below the reinforcement rods you can use designer tiles like mangalore-tiles placed in perfect fit with other filler materials that are placed in-between reinforcement rods.... during casting hand-vibration is must and we cannot use any machine vibrators since the filler material may damage... the mix needs to be rich as to hold the filler materials tightly... these are couple of details one must keep in mind... incase you are in need of more information you may write to me at architect.solution@gmail.com

Good Luck

Rekha
Chandran Rekha Jetty
Filler slab on RCC columns
Hi... One more thing.... between the reinforcement rods filler materials upto 2" deep can be used and below the rods filler materials like designer tiles only can be used since they are of just "cover" thickness...

Rekha
Chandran Rekha Jetty
Filler slab on RCC columns
Hi... One more thing... shear regions are all along the beams and columns... the reinforcement in that regions remains as in any solid slab (two-ways/one-way)......you can design your filler slab reinforcement only in non-shear regions and in non-shear regions the reinforcement may be widely spaced... general spacing in non-shear region is @1ft c/c, where as in shear zone the general spacing is @100c/c... i.e almost 3 times wider is non-shear zone...wherever the rods crank i.e L/4 OR L/5 region from the edge of the effective length, the filler material should be of lesser depth. Thus it is better to plan the interior ceiling pattern based on the depth available in the cranked region of the rods.... generally the mangalore tiles below the reinforcement rods in the cover region are held in good grip due to corogations in them. Filler materials can be designer bricks... these are generally held tight since the material of these bricks are concrete which tend to get monolithic with slab totally.... in case of pots they are held tight in concrete due to compression on the pot surface....

Hope this answers some of other vital points

Rekha
Chandran Rekha Jetty
Filler slab on RCC columns
hello Rekha.

what advantage does a filler slab offer over the use of a conventional conrete slab? is it because of weight issues?
Jofer Magsi
Filler slab on RCC columns
hi im final year student of architecture ,doing my thesis on zero energy housing.i want to use filler slab and rat trap walling,it is possible for urban region with 6 story building,
Piyush Verma
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