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IS IT POSSIBLE TO DESIGN A 100MM SLAB, if the required depth is 130mm as per L/D ratio??

 
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renju mathew
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PostPosted: Fri Mar 01, 2019 10:31 am    Post subject: IS IT POSSIBLE TO DESIGN A 100MM SLAB, if the required depth is 130mm as per L/D ratio?? Reply with quote

Dear all,

Is it possible to redesign a 130mm TWO WAY SLAB , as 100mm.?

is there any provision for increasing the steel, instead of depth for satisfying the deflection limits?

Thanks in advance.
Renju Mathew
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es_jayakumar
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PostPosted: Fri Mar 01, 2019 2:28 pm    Post subject: Reply with quote

You have to be beware of over-reinforced section then. You may try by trial and error. May utilize the attached work sheet for this.

E S Jayakumar



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mjnasar
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PostPosted: Sun Mar 03, 2019 8:10 am    Post subject: Reply with quote

Eng. Renju Mathew

As the slab moment capacity is more than required,

we can reduce the deflections by camber And

Camber can be provided equal to immediate DL deflection

Regards
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Dr. N. Subramanian
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PostPosted: Tue Mar 05, 2019 4:36 pm    Post subject: Reply with quote

Dear Er.Renju Mathew,

Depth is directly related to the deflection. May be by using doubly reinforced section or over reinforced section you may satisfy the strength but can't satisfy deflection criterion. Moreover over-reinforcement us not a good design option.

Clambering is done in metal sections and not in concrete.

Best wishes
NS


mjnasar wrote:
Eng. Renju Mathew

As the slab moment capacity is more than required,

we can reduce the deflections by camber And

Camber can be provided equal to immediate DL deflection

Regards
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rojanmathewtsy
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PostPosted: Tue Mar 05, 2019 6:30 pm    Post subject: Re: IS IT POSSIBLE TO DESIGN A 100MM SLAB, if the required depth is 130mm as per L/D ratio?? Reply with quote

renju mathew wrote:
Dear all,

Is it possible to redesign a 130mm TWO WAY SLAB , as 100mm.?

is there any provision for increasing the steel, instead of depth for satisfying the deflection limits?

Thanks in advance.
Renju Mathew


You can introduce concealed beams in your slab do that the span may g et reduced and hence it may pass in deflection criteria.
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sunilgoyal
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PostPosted: Wed Mar 06, 2019 3:45 am    Post subject: Reply with quote

Your question is incomplete.
Panel Size?
Edge Condition?
Concrete Grade?
Steel Grade?
Support condition (Wall/Beam)?
Some of the Solutions:
1. Try to detail reinforcement at edges to make them fixed.
2. Reduced steel grade
3. Reduced tension steel and increased compression steel
4. Increase concrete grade
5. Initial cambering.
6. Concealed beams are just stiffening beams provided belowpoint or line load. Not going to help much in deflection control.
7. FEM based design will help you to predict the deflectionproperly.
8. Don't forget to take effect of shrinkage and creep inanalysis, as you are trying to minimize the thickness.
9. Make all attempts to reduce the shrinkage and creep of concrete(low w/c ratio, low cement content, minimize fines, proper curing etc.)
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venkatasalamkl
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PostPosted: Thu Mar 07, 2019 2:40 pm    Post subject: Reply with quote

Hi Er.Renju Mathew,

By adding more compression steel long term deflection can be reduced.

Also, If you had applied stiffness modifiers to slabs as per codal provisions, remove those stiffness modifiers and perform non-linear static analysis in CSI-SAFE(or any other software which has this tool).
Nonlinear static analysis will take care of stiffness modifiers(You need not assign any modifiers specifically).

In addition to above points, Adding more top steel at column junction and reducing bottom steel in adjacent spans will reduce short term deflection (Basically here moment redistribution will be happening and please note this can be captured only in nonlinear static analysis)

The following question is for Dr.N.Subramanian,

Sir
, In your response above you have quoted that cambering can be done for metal sections and not for concrete. Can you please clarify why cambering cannot be done for concrete sections. Because, I have seen in few US projects where Cambering is done for concrete slabs also.(Especilally Flat Slab). Can you please give some insight on this. Are there any specific reasons for not following this in India.
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