Beam / slab interaction

[mathias_peron]

Hi everyone, I'm running an experiment to understand what's the best way to model the beam-slab interaction.

I've read very interesting topics on the forum that partly answered my questions. But I still need enlightening.

A - RC SLAB / RC BEAM

As adviced in the Autodesk university HAndout, a good method to model a beam supporting a slab is to increase its moment of inertia to make it match the corresponding T-beam inertia (see bellow).

However, I'm not totaly conviced because:

1- It is geometrically incorrect. The position of the axis of the beam doesn't match the slab

 -> leads to incorrect stiffness

2- There is overlapping of concrete

 -> overestimation of stiffness.

My question is: Wouldn't it be more accurate to increase the moment of inertiaof the beam to match a corresponding rectangular beam bellow the slab (new inertia = (bh^3/12)+(bh)d²) ? In doing so, we can still choose to design the beam as a rectangular or a T, and with a correct geometry (see bellow).

B - RC SLAB / STEEL BEAM

I tried to use the rigid links to model the interaction between a concrete slab supported on the flange of steel I beams. I couldn't understand why the moment in the beams is so low. Can someone explain me?

Have a nice day,

Mathias.

[Artur.Kosakowski]

HI @Anonymous

The point is to increase it IY by the factor of IY for T shape for middle or L shape for edge beams / IY rectangular shape rather than just any e.g. 2 for all beams regardless of their shapes and sizes.

Check the model I attached to my previous post.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

Dear Artur
I can't find the model.
Can you please sent it to me through my email: vntibaziyaremye@gmail.com

[Romanich]

Hi @Anonymous,

You may find this topic also useful:

https://forums.autodesk.com/t5/robot-structural-analysis-forum/api-macro-creation-of-quasi-t-amp-l-rc-beams/td-p/5485265

[Anonymous]

Hello Mr. @Artur.Kosakowski 

when I'm increasing the Iy of beam it wouldn't be equal when I'm expressing the As with equivalent Ac using n and not expressing the place of the analysis axis of beam & when I want to analysis for a cracked section shouldn't the value off I(inertia) be reduced by reduction factor.