Reinforcement area

[audryszazx]

Hello,

I know there is no single answer to this question, but I'll try here... I try to model one slab with 6 different types of mesh. Slab dimensions is 2m x 10 m. With linear supports at the end and one nodal support in the middle of slab. I take 6 types of mesh:

1. 2m;

2. 1m; 

3. 0,5m;

4. 0,25m;

5. 0,1m;

6. 0,05m;

Everytime I take smaller mesh size I get bigger reinforcement area in nodal support. I know that smaller mesh size shows better results, but it takes longer to calculate. 

My questions is:

1. How do you think, what is the best mesh size? What mesh size do you choose for calculating slabs?

2. If i take mesh 0,25m and reinforce top layers (X direction) with 12 cm^2/m (ø16, 200mm), do I make a big mistake because it requires 21,7 cm^2/m (ø18, 200 mm) with 0,1 m mesh? 

I have bigger model with concrete slabs and walls, and if I take 0,2 m mesh, i get very big reinforcement area, but if i take 0,25 m mesh, it looks quite good. So i do not know what mesh size is good enough to continue slab reinforcements. Thanks for helping. I will add RSA 2011 file as example.

[Krzysztof_Wasik]

Hi @audryszazx 

I would recommend the following.

• Using advanced support properties defining support  (column) shape
• Defining mesh size about 1/3 of support size (edge length or diameter)
• Usinr reducing forces above columns and walls while reinforcement calculation.

Refer to video

[audryszazx]

Hello,

yes I do that in my main model.

But I still get bigger reinforcement in these red zones, when I use smaller mesh size.

So if my walls width is 250 mm, I should take slab mesh size about 80 mm? Now my mesh is 250 mm

Columns are 400x400.

[Krzysztof_Wasik]

Hi @audryszazx 

I would use mesh size near walls equal to half of wall width. Over supports I would use mesh size about 150 mm. Concentrations are caused by numerical effect for Finite Element method (singularity in concentrated supports or under concentrated nodal forces) in those regions calculated forces incerases while mesh size reducing.

[audryszazx]

So all slab mesh is 0,15, and at the wall 0,125?

And what about this question:

2. If i take mesh 0,25m and reinforce top layers (X direction) with 12 cm^2/m (ø16, 200mm), do I make a big mistake because it requires 21,7 cm^2/m (ø18, 200 mm) with 0,1 m mesh? 

[Krzysztof_Wasik]

Hi @audryszazx 

I would suggest 

wall /slab connection region about 0.125 m (in slab and wall)

column region 0,150 in slab (but it can be 0.125 as well)

In other slab /walls region (in distance from supports) mesh can have bigger size (0.500).

[cerveiramatheus]

You also can handle this with a non-linear plastic analysis concept.