rcchs Reinforced concrete circular hollow section

[Antrox]

Hello,
I was looking the rcch section but I didn't understand how the software sets the section dimensions.
I see that you can setting the outer diameter and the inner diameter of the section.
But how much is the thickness of the steel? Has this section one inner steel skin or is it a double skinned?

My problem is the modelling a micropile, I could use this section if it's possible to change the thickness of the steel (but i have to put a null or very small value in the outer steel).
Thanks in advance

Alessandro

[fbianchi]

Hi Alessandro,
in this section, as in all the reinforced concrete sections, you can define the reinforcement bars in two different ways (as it is stated in the Help System):
1- by editing the reinforcement pattern;
2- by entering the respective area and sectional coordinates (the latter being defined in the local coordinate system of the section).
I think that in your case you have to opt for the latter, because you only need to define the bar's coordinates.
Federica

[fbianchi]

Hi Alessandro,
maybe I misunderstood your question (I imagined that you want to change the reinforcement pattern). On the other hand, if you need a composite circular section (in order to define a steel jacket) the only one available is the "ccs", in which you can assign the steel thickness directly (but it is not a hollow section...), otherwise you can use the rcchs by assigning a steel material to the cover and by changing the R/C cover thickness as you like in the Project Settings (Project Settings -> Elements).
Federica

[Antrox]

Thank you for your advice.
Now I'm using a rccs section with reinforcement bars in place of the interior steel jacket.
I see that if I use this section with an elastic frame, the stiffness doesn't account for the bars (ok, no problem). So I try to use a Force based inelastic frame with the default value of fiber and integration sections.
There something strange because the stiffness in the FB element is too small. I calculated it by means of a eigenvalue analysis.
I.e.if I use a section with no bar, the stiffness in the FB element is less than the elastic element with the same section. I was expecting a same result instead the natural period of the fiber element is higher than of elastic frame.
Do you know why?
Thanks

[seismosoft]

Dear Alessandro,

Apologies for the delay in addressing this issue.

We confess not to fully understand the problem you are experiencing, which we thus were not able to reproduce.

Perhaps you will want to send us the files in question, so that we look into it?

Thanks,

Seismosoft Support

[Antrox]

It's not necessary the file, I'll try to explain me better:
I made these 2 attempts:
SECTION: rccs section with no bars
FRAME: 1)Force based inelastic frame
2) ELastic element
Force based inelastic frame comes out more flexible than the elastic element.
I checked it with a modal analysis (one time with elastic element and one time with force based inelastic frame)
Why?
Thanks