Plate and shell reinforcement type

[eiriknor]

I have some pre-fab slabs that shall be the deck in a parking garage. On top of these slab there shall be 100 mm cast-in-concrete. The slabs should transfer live loads to the columns, but also wind loads from the columns through the deck and into the walls that support the whole structure.

Doing a reinforcement calculation with "bending + compression/tension" get a bit messy reinforcement map. Ì wonder if I can do one calculation with this "simple bending"-option and reinforce the slabs with this and the cast-in-concrete (if I get some reinforcement in the upper layer).

Then do a re-calculation with "compression/tension"-option and put all of this reinforcement in the cast-in-concrete part.

I`ve tried this, and I sure get a much more "clean" reinforcement-map in both cases. But I`m afraid I`m missing something here and my structure will collapse when it starts to blow.

Hope someone can help me out with this one.

[Artur.Kosakowski]

I think you need to answer yourself a following question - are the in-plane forces (tension / compression) small enough to be ignored for reinforcement calculations? If yes, then you can select the simple bending mode, otherwise you probably should select tension/compression + bending instead. You may also try to switch off calculations of minimal reinforcement to check how the reinforcement distribution would looks like. This should give you a better understanding of the situation when the tension force causes the need for minimal reinforcement in the slab.

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[eiriknor]

The tension/compression forces are not samll enough to be ignored, that I know for sure. The "simple bending - compression/tension" option gives me no control of how much of the reinforcement is caused by the membrane forces. Since I have these pre-fab slabs I`m not able to have continous reinforcement in the lower part of the deck, only in the "cast-in"-part. I`ve done a couple of calculations and it seems for me that in my case regarding the reinforcement that "simple bending - compression/tension" "=" "simple bending" + "compression/tension".

Eirik

[Ch.Charitidis]

Hi,

I have been having a similar issue and I am wondering if my reasoning, although quite simplistic, has any merit.

If the design is performed once against tension/compression and once with simple bending and we add the reinforcement quantities, shouldn't that reinforcement be then equal to the reinforcement provided if designing with bending +compression/tension?

I have tried this but the bending+compression tension produces more reinforcement than the sum of the two separate designs combined. Any idea why that is happening?

[Artur.Kosakowski]

Bending + tension/compression

case1: bending + small tension :

top under compression (no reinforcement)

bottom: tension + tension -> large reinforcement

case 2: small compression - no reinforcement

case 3 small tension

 top and bottom small reinforcement

Final reinforcement:  

top: small reinforcement

Bottom: large reinforcement

-------

Bending:

case1: bending :

top under compression (no reinforcement)

bottom: tension ->  smaller than large reinforcement)

Tension/compression

case 2: small compression - no reinforcement

 case 3 small tension

 top and bottom small reinforcement

Final reinforcement:

top: small reinforcement

bottom: smaller than large reinforcement