Slab vs beam (deflections and cracks)

[Jummybear]

We are trying to find out how correctly Robot calculates deflections and cracks for slab with provided reinforcement. I didnt find ant verefication manuals on this theme in document named "Verification Manual EU codes". For beams its ok and slabs only punching is ferifed. I have made a simple test: 2 models, first one is slab model 1x6x0,25m, meshed and reinforced correctly and finally verifed for deflection and cracks. And a beam with the same section parameters, same reinforcement, verifed in rc modul for deflection and cracks also.

Slab model gives me bigger deflections and crack widths...

1. 1x6x0,25m with bottom reinf. 12-100. Slab model: defl. ~ 27mm, crack ~ 0,22mm. Beam model: defl. ~ 20mm, crack ~ 0,18mm

2. 1x6x0,25m with bottom reinf. 16-200. Slab model: defl. ~ 30mm, crack ~ 0,26mm. Beam model: defl. ~ 21mm, crack ~ 0,24mm

3. 1x6x0,25m with bottom reinf. 16-100. Slab model: defl. ~ 19mm, crack ~ 0,10mm. Beam model: defl. ~ 15mm, crack ~ 0,08mm

Any comments?

[Artur.Kosakowski]

First of all check if you have exactly the same values of bending moments and cover (arm of forces) for the beam and the slab. You may also want to check the results obtained with the stiffnees update method.

See also: http://forums.autodesk.com/t5/Robot-Structural-Analysis/elastic-and-nonelastic-slab-deflection-verif...

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Jummybear]

I cant find a mistake or the problem issue. I will upload 2 files: one witj slab model and another with beam. Parameters are the same: reinforcement 12-100, cover 25mm, concrete C30/37.

Now i get for slab model defl 25,8mm, crack width 0,19mm and vs beam model deflection 16,8mm and crack wodth 0,16mm. Bending moments are similar: 67kNm for ULS and 50kNm for SLS. Concrete strength (C30/37) and cover (25mm) should be the same also.

PS Results for slab are also done with stiffness update method.

PPS I can take the cracks difference of 20% between two models, but for deflection its about 50%...

[Artur.Kosakowski]

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.