limit lenght for a nonlinear beam column element

[aizen]

Hi everyone


There are limits for the lenght of the nonlinear beam column element?

Is it possible to use a element with section diameter of 400mm and a heigth of 100mm?


I have tried to use "local" element as zerolength fiber element to simulate a particular behaviour of one section (section without height) but the analysis do not run.


Can I use nonlinearbeamcolumn element very short without to have wrong results ?


Thanks

[fmk]

there is no limit on length .. however, for short beams the response is not governed by flexure but shear .. so using the element would be a poor modeling choice .. you could try aggregating a section with a material to represent the shear response, but there will be no shear-moment interaction in such a section.

[aizen]

Dear fmk

Thanks for the help.

My problem is particular.

I have to simulate a concentrated damage at the base of a r.c. column. The damage is concentrated at one section.
This section has rebars less resistent than ones of the upper portion of the element (in this section some connections have been placed, the rebars of the anchorages are weaker than the longitudinal bars used in the upper part of the element ).

I have applied a horizontal cyclic load at the top of the column. The section less resistent at the base of the element, has greater demands (trend of moment for the particular load patter) and being less resistant, it will be deformed more (greater rotations).

The fiber model has been built using one element at the base (short element 0.1m - 0.2m) and one element (long element 1.5m) for the upper part of the column.

The base section is "like a hinge" and so the upper part of the model must rotate as a rigid body and so there are minor deformations of the longitudinal rebars of the upper sections.

So I want to simulate a fiber section at the base where deformations of the longitudinal rebars concentrate. I want simulate that deformations of the longitudinal bar at the base section are greater than ones of the section of the upper element.

So is it correct using a such short element at the base?

Why does not a zerolenght fiber element work in this case?

If i use a zerolenght fiber element in this case (section at the base less resistent of the upper section) the analysis does not run correctly and stops at first (after a few short cycles)

thanks

aizen

[aizen]

Dear all

Can someone help me?

I thank FMk for his help but my problem for now it is not the shear deformation that I have to consider later.

I am not sure about the type of element implemented in noninearbeamcolumn element and so I have not reference about the limits geometrical in the use of this element (ration between diameter of the fiber section and the height of the element)


My problem is simple.

I have to model one r.c. column with a particular base section where deformation are concentrated.

At the base I have greater rotation concentrated (hinge at the base).

I have to apply a vertical load and a cyclic horizzontal displacements history at the top of the column

In my first test I have used one nonlinearbeamcolumn element with fiber section for the column and one zerolenght fiber section element (steel and concrete unconfined and confined). The model does not run.


In my second test I have used a nonlinearbeamcolumn element for the column and a nonlinear beam column element very short (500mm diametr of section and 50mm height of the element) with only two integration section at the base.

In my third test I have used a nonlinear beam column element for the column and two short nonlinearbeamcolumn element with only two integration section for element.

The third case shows a better distribution of the deformations


The model runs but I have a doubt about the reliability and accuracy of the results.


Thanks

Aizen

[aizen]

Can someone help me?

[fmk]

if you are going to startbreaking up the column into individual elements use the dispBeamColumn instead of the forceBeamColumn(nonlinearBeramColumn)

[aizen]

Dear FMK

thank you a lot.

thanks for your kind answers.

I will try to use this element.

is it possible to have a reference of the author of this element (author of the theory and the author of the implementation in opensees) to study carefully the use and the geometrical limits?

thanks

aizen