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slab

slab

(OP)
what if a one way slab design used in actual instead of two way (the slab should be designed as 2way)

RE: slab

You can expect cracking, probably undesirable cracking, in the lightly reinforced direction.

RE: slab

(OP)
the slab is supported by a 1.4m high column (200mmx400mm)(simply supported),slab dimension is 3.1m x 3.5m ( house is designed to carry a 100mm thk roof slab )

RE: slab

(OP)
what is the best remedy of this case ?

RE: slab

A sketch would help, as I am not sure I understand. You say it is supported by a (one?) column. How does that work? And what does the roof slab have to do with this slab?

RE: slab

(OP)
Ground floor slab will carry a CHB walls and a Columns (180mm x 400mm) supporting roof slab

RE: slab

Why do you need to remedy? why is the floor to floor height so small? and are you planning to subject this model to earthquake loads?

http://www.nceng.com.au/
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

RE: slab

Quote (cegrace1485)


Ground floor slab will carry a CHB walls and a Columns (180mm x 400mm) supporting roof slab

From the Ground Floor Framing Plan you provided it is 2-way slabs supported by beams in 2 directions. Supported by columns at intersection of alpha-numerical grid lines, and type C1A "columns over" at some perimeter grid locations that evidently support a roof of some type.

The slabs should be designed with reinforcement in both directions, and provide sufficient capacity for flexural actions in both top and bottom of the slab. Check your applicable building/concrete code for termination and curtailment of rebar to for positive and negative bending, in both directions.

The framing plan is obviously not showing reinforcement, but the arrows in 2 directions adjacent to the slab designation "S1" indicates that 2-way slab action is being considered. Hopefully there is a reinforcement plan/layout drawing or at least a schedule of rebar, each way, T&B.

A 180mm column is very thin. Going to be tough to make vertical splices and concrete cover work and still place concrete.

And the "B1" beams are only 200mm wide - again, going to be tough to make such narrow beams "constructible".

Not sure what "CHB" walls are - concrete hollow block? If so, the load tributary to the walls (from roof plus self weight) need to be included in the design of the ground floor beams where shown, eg at grid B2.

RE: slab

Quote (rowingengineer)

why is the floor to floor height so small?

The 1400 column height referred to is from foundation to ground floor, not ground floor to roof.

RE: slab

fair enough, but I still want to know what this is all about? is this constructed or what is the problem?

http://www.nceng.com.au/
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

RE: slab

As Hokie intimated, it's a serviceability issue. How sensitive is the floor finish -- and the owner -- to cracking? If it's carpet and pad, no problem. If it's tile or exposed concrete, expectations will require some managing.

The only remedy that I can think of is to possibly detail your floor finish to "float" somehow if it's sensitive.
 

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: slab

I believe the Fyfe Co has used their composite fiber system to reinforce under designed or cracking slabs before. You'd have to contact them to get details. But, that might be simpler from a construction stand point than other methods of retrofit.

RE: slab

(OP)
this is already constructed (a month ago)

RE: slab

Quote (cegrace1485)

this is already constructed (a month ago)

Okay, but exactly what reinforcement got placed to the slabs?

Even for a 1-way slab, there is temp and shrinkage rebar in the orthogonal direction.

Was top and bottom rebar provided?

Do you have records of what got placed vs what was designed etc?

If YOU can define what is the problem, WE can all be of more assistance.

RE: slab

(OP)
the one that is placed is for one -way slab reinforcement

RE: slab

(OP)
my worry is for the seismic reaction of the structure (since it was designed as 2 way)
for now I didn't see any sign of cracking. We have provided proper curing procedure..but I don't know in the next few weeks or month , years..i think the crack will occur eventually due to wrong reinforcement

RE: slab

Ingenuity asked for "exactly" what reinforcement was placed, in both directions, top and bottom. Unless you can tell us that, we can't help. As we don't know you, we don't even know if you know the difference between one way and two way reinforcement.

RE: slab

(OP)
10mm diameter grade 40 - both temperature and shrinkage reinforcement is provided

RE: slab

We are all engineers here, not dentists! It is like 'pulling teeth' to get relevant info from you!

Anyway, what SPACING of M10 grade 40 (ksi I presume, although you are mixing SI and Imperial units) in both directions, T & B?

RE: slab

(OP)
oh sorry for that.. main reinf spaced at 200mm . same as the shrinkage reinf - 200mm o.c

RE: slab

@ c/c?

RE: slab

Ok, so M10@200 both ways, so NOT really one-way reinforced!

Top and bottom rebar continuous?

Spans are pretty damn small - 3.5m with continuity on at least 2 adjacent edges.

Slab thickness?

Is this project in the Philippines? The adopted framing and spans remind me of framing systems I used to see from PI back a decade or so ago.

RE: slab

My guess is that the main reinforcement is yet to be unveiled. This is an interesting ride, however.

RE: slab

Quote (Trenno)

My guess is that the main reinforcement is yet to be unveiled. This is an interesting ride, however.

I think you are right - as-built MAIN rebar yet to be provided.

Confused!

RE: slab

(OP)
here is the followed reinforcement detail -(reinforcement @ long span) - short span not provided

RE: slab

Seems as though that detail is a mashed up typical detail and actual section...

Are the beams 150mm or 200mm wide?

Using 275 MPa steel, I think the reo provided is slightly less than min. reo? (According to the AUS standard - 390mm2 < 480mm2)

RE: slab

(OP)
200mm wide

RE: slab

100mm thick suspended slab! Wow, how do you build such thin slabs!

We do MIN 100mm thick slabs for slab-on-grade (ground) with top reinf only.


20mm MIN top and btm cover, 4 x M10mm ∅ for rebar, so you have maybe 20mm clear between top layers and bottom layers.

Damn, I struggle with 150mm slab suspended thickness.


Is your code-specified min. reinforcement satisfied?

Is min. slab thickness satisfied for fire transmission/insulation between floor?

Deflections?

Floor finishes - mortar bed and ceramic tile?

Concrete block wall supported by these slab - brittle finishes!

RE: slab

bugeyed

RE: slab

Agree with Ingenuity. The concrete elements are very thin, and constructability is questionable, especially with unsophisticated workers.

cegrace1485, you are obviously not a structural engineer. This site is for exchange of information and advice between practicing engineers.

RE: slab

I don't see the absence of slab top steel adversely affecting seismic performance here as long as your beams and columns were constructed properly. As Hokie said at the top, the primary consequence here will be top side cracking.

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: slab

KootK,
That's not what I said. I was talking about inadequate reinforcement in one direction, whether top or bottom. Based on the section he attached, he does have top bars, at least on the drawings. But from his various descriptions, who would really know?

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