Drop panel effect on reinforcement 1

[Robert-32]

I am wondering why the analysis of flat slab with drop panel is giving nearly the same reinforcement as without drop panel. Thickness of slab is 30 cm and total thickness at drop panel is 45 m. spans are 11 m. columns 70*70 cm.

 

[Celt83]

Assume this is as reported in software? What software is being used?

There are several possibilities:
- Software package options for inter-cross section trimming not set properly
- flat slab steel governed by strength vs slab+drop steel governed by minimum area
- If a bottom reinforcing mat is present with a drop panel this layer of reinforcement will usually be tension steel when doing a strain-compatibility analysis at the column critical section.

Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

 

[KootK]

In a design strip that includes both a drop panel and some non-drop panel slab, there is always a question of whether or not the slab outside the drop panel should be designed using d_drop or d_slab. My money says that your software is using d_slab. That may be a) within your control and b) altogether appropriate.

 

[rapt]

You have not given the drop dimensions other than depth.

Normally drop depth should be considered for the column strip reinforcement if the width of the drop i adequate.I assume with those slab/drop depths the slab is PT.

 

[Robert-32]

Thank you all for your input. The software I use is finite element package. The problem still not solved. There should be a reason why the reinforcement is not dramatically reduced by adding 1/2 the slab depth using drop panels. drop Panel dimension is 3.8*3.8 m, span 11 m.

 

[hokie66]

The drop panel attracts moment...stiffness. Amount of steel required is directly proportional to moment, and inversely proportional to effective depth. Your software may be doing the computations correctly, but you should pull out your trusty paper, pencil, and calculator and check it.

 

[rapt]

Finite Element determines stresses and strains and from that Moments and Shears. It does not determine reinforcing quantities. That is a design add on that has nothing to do with FEM except to use the moments provided.

You would have to ask Masterseries! The drop panel depth should be considered for the column strip reinforcement.

Ask them how good their deflection calculations are for cracking and long term effects as well. As Masterseries does not do PT, this must be an RC slab with an L/d of about 42. A 30cm slab spanning 11m does not work.