Modelling a wide cap beam in Robot

[Anonymous]

Hey guys

I have difficulties modelling a wide cap beam with the dimensions of 4m*12m (in the plan) and varying thickness from 0.6m (on the edges) to 1.5m (in the middle part). 4 girders sit on the cap beam from each side. The cap beam is supported by a 4m*4m concrete box column. due to large dimensions it has to be subdivided to few elements or possibly a shell element to represent its actual behavior. 

I attached a hand sketch of the cap beam. please give me an idea what to do ?

Thanks

[Rafacascudo]

columm - bar with rigid links on top

slabs - shell with variable thickness

Something like this

You can enter the missing slab( or top of columm) part as a load on columm top node 

model attached Robot 2018

[Anonymous]

Thanks Rafael

But in fact the top surface of slap should be perfectly flat and horizontal. Also is it possible to define non-prismatic shells in 3D frame mode since this option is only available in shell mode, and when I switch to shell mode to define something and switch back to 3D frame I get errors during the analysis.

Regards

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

As I already started my picture  Just to illustrate the way it was done by @Rafacascudo (thank you) and in case you want to model have the middle part of the cap as well 

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.

[Rafacascudo]

the slab top surface not being horizontal is just a detail . You can be sure the the correct slab stiffness will be perfctly represented even though its geometry is not according to real life.

You can only define slabs/walls (as structural members) in a shell structure type model !!

You cannot go back to frame 3d type expecting the shell objects will appear there like magic 

[Anonymous]

Thank you Artur. It was very helpful.

[Rafacascudo]

Life is hard ...

[Anonymous]

life really sucks, I don't know why the hell I chose engineering and why the structural engineering MSc 10 years after my BSc...?!?!

I should blame dad lol

[Artur.Kosakowski]

Hi @Rafacascudo

With all the help you provide it is actually pretty easy 

I really do appreciate it.  Thank you.

[Anonymous]

I was just wondering if there is anyway to make the section independent from points coordinate or create it using relative dimensions ?

I tried your way and it perfectly worked in Plate mode, but once I copy it to another 3D frame file the shape gets distorted. and If I define the slabs in a 3D frame file, the top surface is drawn with a slope by default. 

Maybe there is way to draw it in plate mode and merge the segments and make a solid object ?!?!?

[Rafacascudo]

"Shell"structure type = "3d frame" structure + shell objects (slabs, walls).
You will NEVER get a perfect geometry for this model. Slab face can be horizontal if you model an inclined panel as Artur suggested in his sketch. But your thicknesses (65cm,150cm) will not be vertical.

If you really need a 100% perfect geometry model , use Solid structure type.
But then your life will really become hard 🙂