Flat Slab with thickened concrete at column locations

[Anonymous]

Hello!

I have a simple question with regards to Slab design:

Please refer to the image below:

The above image is a cross section of a concrete floor slab that will be thickened at column locations as shown by the red lines. The whole structure will be concrete including the columns.

My question is how should I model this structure in Robot?

[Rafacascudo · Accepted solution]

If you need the slabs (thin and thick) to leveled at the top ,then you will need to use rigid links  to connect panel nodes from both ,since they will need to be modelled at different levels

[Anonymous]

Hello again Rafacascudo!

If you don't mind me asking, could you show me a short video as to how you would go about using it? I gave a shot at it however I'm unsure how to use the rigid link tool. Also, how would that level the top of the concrete floor as shown in my drawing?

[Rafacascudo · Accepted solution]

Something like this

[Artur.Kosakowski]

If you may assume that in-plane forces can be neglected you can simply define all panels at the same level and make the ones over the columns thicker. 

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.

[Anonymous]

So to summarize:

You create 2 slabs of 2 different thickness with the same finished elevation and then connect them together using the rigid links option. Looks straightforward to me 

I have one simple question: The "range radius" option. How did you decide on that value and how does it affect the model? 

Also when I throw in concrete columns underneath the thickened portion, is there anything extra I should consider with regards to the Robot model (i.e. special conditions like the rigid link option for the above slab) or just model them normally?

[Anonymous]

In addition to my above question, does the connection vector matter in terms of its direction (i.e. going from top panel to bottom panel or bottom panel to top panel)? And how about any linear releases? Would I have to use them for a slab like this with columns?

[Rafacascudo]

Range - It´s well explained here http://help.autodesk.com/view/RSAPRO/2016/ENU/?guid=GUID-88C4C842-5D90-4E85-8F8C-D47D6E474E29

Thickened slab and columns - You have several modelling options . It depends on your "enginneer" evaluation. If slab is too thick compared to the thinner slab , you can model it as a rigid block using "panel calculation model" .

  If you model it as a regular shell , and is getting slab moment spikes on column top ,you can use " reduction of forces above columns and walls" (  http://help.autodesk.com/view/RSAPRO/2016/ENU/?guid=GUID-E4E8BE33-DCD2-4343-824C-447A1AB5ECA0 ) , or use rigid links to simulate the column perimeter.

 Vector - I would do from the thicker slab nodes to the thinner slab nodes , but I can´t see any difference on the results doing the inverse way.

[Anonymous]

Thank you very much 

I can do some reading on it to get a much better knowledge on it.

[ville.kantelinen]

Hello,

I need to design a floor slab supported by piles, basically a column slab. I have made several models and got different results from them.

- There are "drop-downs" cast over columns (= piles). The slab and these drop downs are cast over piles as a single monolithic structure without seams.

- It's essential that cracks in the slab must be absolutely limited to 0,3mm maximum.

Here are two different models I have made for comparison.

The first one has drop downs modelled only there, where h = 800mm. I was fine with the results.

The second one has drop downs also over single columns, where h = 600mm. The required reinforcement goes up drastically with the drop down at the vicinity of singe columns, where slab is 350mm (slab where h=600 has significantly larger "d" value, so reinforcement doesn't build up there).

Obviously with the drop down there is more rigidity over the column, which takes more bending.  What makes me worried is that with the second model there is over x1,5 times more reinforcement at the top of the single columns and just a little bit less at the bottom at the sagging area of slab. I have "reduction of forces above columns" activated in both cases. Is it so, that with the drop downs, the "reduction" -functionality doesn't affect the larger panel at the end of rigid links? 

I need to find the most economic reinforcement, as there are lots and lots of these slabs coming up. I'm looking to build the most "realistic" model as possible, as I need to limit the cracking at 0,3mm max everywhere in slab. I'd like to hear from more experienced Robot users and designers how would you model this kind of slab? Which of these models results do you think would better represent the reality? 

[Anonymous]

can somebody please enlighten me with this, i have attached a picture of my trial drawing in robot im just wondering why the column on top ended up with bigger section & bigger diameter of bars eventhough the column below has much higher axial load than the column on top.

thanks in advance.