relation between steel bar/concrete amounts

Replies to This Discussion

Permalink Reply by Rafael Pastrana on April 15, 2015 at 2:49pm

Hi Patricia,

I think there is no such a "direct way" to just get of getting the steel rebar percentage in a concrete structure straight ahead from Karamba. 

As far as I know, Karamba is a finite element method piece of software which can for sure give you the internal forces (axial, bending moment, shears) by performing a 1st or 2nd order analysis, and is able through one of its core algorithms (OptCrosSec),  to design steel structures according to the Eurocode 3. 

Unfortunately, there is no support for reinforced concrete "as is". What you could do is to take this internal forces for all of your members, and then design outside of Karamba (say manually or by a spreadsheet), the elements you need to design. 

I´m pretty sure there are plenty of graphs and charts out there to get steel rebar percentages according to your concrete elements´dimensions and internal forces.

Hope this helps :) Best,

Rafael

Permalink Reply by Aryan Shahabian on April 17, 2015 at 10:48am

Dear Rafael,

I have a more or less similar question. I'm making a rough model of a reinforced concrete structure of a high-rise building. I won't go into details and calculations and positions of steel bars.  I only need to see if the structure I'm designing is stable in conceptual stage. In such rough models, can I use concrete material properties instead of RC? If yes, would the size of maximum displacement as well as size of elements (thickness of shells) be similar to RC?

Best,

Aryan

Permalink Reply by Rafael Pastrana on April 17, 2015 at 3:28pm

Hi Aryan,

I think that deflection-wise it could be okay to assume concrete properties for having a first glimpse into the deformation of your structural system in such a conceptual stage. 

Theoretically speaking, I believe one of the ways of having a more accurate deformation simulation is by calculating equivalent cross-sections (say, how much extra concrete area you would need equalize the EI contribution of the reinforcement steel, which would make your concrete cross-section "biggerl), but then again that would be affected by crackings in concrete which would tend to reduce the effective concrete area in the end... Then, it becomes quite tricky and perhaps it would require far more depth than what you may need...

For the elements sizing, if this is to control deflections and deformations via making your elements´cross-sections bigger or thicker, then this should be fine.

There are a few rules of thumb as well which could help you a bit to size your structure (i.e. an appropiate depth for a concrete could be around span/10 or span/12). 

Hope this helps :) 

Rafael

Permalink Reply by Aryan Shahabian on April 17, 2015 at 4:53pm

Thank you Rafael! That's helpful.