Hello Reza,

I think you should check the material properties again. It means that you should define elasto-plastic or plastic behaviour for concrete and also its reinforcements to have reall behaviour.

Hope this help you.

Best,

Azadeh

Thank you Ms. Amiri ,

I defined concrete02 for concrete, steel02 for reinforcement, and I use forceBeamColumn element which I think that it can capture the non linearity behavior. I checked the material many times, but it seems that I made a mistake somewhere which I could not find sofar.

I once got similar results for beams without compression reinforcements

It is clear that the column's end-section shows a brittle failure like an unconfined concrete end-section.

You must have a confined concrete end-section to get a ductile mode of failure. This can be done first, by applying a cage of dense transverse confinement reinforcements having a ductile steel rebar material, second, by calculating the confinement concrete properties (yield and ultimate deformations , confined concrete stress) and third, by defining the new confined concrete constitutive law which will be an almost elastic perfectly-plastic curve with a large ultimate strain.

I believe that Athanasios is correct. Your results are typical of what one might expect for unconfined concrete. The Mander model (or some other if more appropriate) would be used to determine stress-strain properties of the confined concrete, which is a function of how much transverse reinforcement is present in the section.

Dear Mr. Bakalis and Mr Huff,

I really appreciate it. When you say "end section", do you assume the lumped plasticity? I used the distributed plasticity, and I did not define any hinge.

You are definitely correct about the confinement, but even without confinement, based on my calculation, I should have ductile concrete crushing which I do not.

I even calculated the confinement parameters (f'cc, epsilon_cc). Although the confinement ratio is low, but it does not change that much.

I also added the same amount of reinforcement at top as a compression steel, but not that much change.

I will double check again, in case I did something wrong.

Thank you again.

Whether lumped or distributed plasticity, the material properties - stress vs. strain - for the confined concrete are the critical parameters.

To get a ductile mode of failure, you must define a confined concrete section only at the base of the cantilever column. The (σ-ε) concrete law should describe the confinement properties regardless of how the plasticity is modeled. I think you must examine the properties of your concrete material more carefully. Τhe plastic area should be quite extensive.

Many thanks.

I know that the amount of each parameter is important in stress-strain relationship. I think that the only differences between confined and unconfined model in OpenSees is the amount of stress and strain which I put the confinement parameters based on the Mander Model, and even I tried to put different amounts to see the sensitivity, but it did not change that much.

As you can see here in the above graph, it fails suddenly which I expect a little ductility, and it fails at about 0.22" for a 60" column (0.36% drift). My question now is: this displacement is reasonable, and if it is not where the problem(s) is.

A typical reinforced concrete column section with a shear span 1.5 m shows approximately 0.5% - 1% drift at yield (yield chord rotation) depending mainly on the section height h and the steel rebar yield deformation e,sy. To be exact, a section analysis must be performed. Approximately the curvature at yield for a column section is given by the following equation: φy=2.05*e,sy/h. From this value, the chord rotation at yield is calculated by the equation θy=φy*Lv/3, where Lv is the cantilever height, taking into account the bending deformations only.