How to record totol acceleration?

[kwaklab]

I can't find option to record total acceleration. In other way to get total acceleration, I sumed relative and ground acceleration. But it is much different to theoretical value.

Could you tell me how to get total acceleration..

[silvia]

what type of input did you specify?

i do believe that the output may already be in absolute-acceleration terms.

[kwaklab]

What is the definition of absolute acceleration? Is it mean equally total acceleration which mean sum of relative accleration and ground accleration?
I applied earthquake load by using uniformexcitation pattern. After comparing with theoritical solution, opensees recorded relative acceleration, velocity and displacement. So I want to know how to get total acceleration not relative one. As I mentioned previously, to get total acceleration, I sumed relative accleration and ground accleration. But, as you know, because numerical evaluation ( ex. linear acceleration method, average acceleration method...) involve period elongation, I can't get total acceleration.

[silvia]

you should check this using a cantilever column with elastic stiffness and a mass.
try three stiffness cases, very very small stiffness, medium stiffness, and rigid stiffness.
are you inputting acceleration or displacement at the base?

[fmk]

you can do a multi-support exciatation instead of a uniform suppport .. in multisupport
the movements are absolute, just apply the same ground motion DISPLACEMENt to all
the support nodes .. relasing fixity in dirn of motion.

[kwaklab]

As I said, I used uniformexcitation pattern. And as your recommandation, I check two extreme cases.
When I applied very small mass, accleration recorded by opensees was very small. And when very large mass, it is almost same as ground acceleration except sign. I think that If it is total acceleration, it should be almost same as ground accleration when I applied very small mass and almost zero when I applied very large mass. But if it is relative acceleration, it is understandable.
I am a little confused. Could you answer after checking these two cases?

[arbarbosa]

An ideia is for you to check the acceleration at the nodes that are fixed. I tried with example 5.1 and I get zero acceleration at the base of the columns. So I too believe that the acceleration is the relative acceleration.

[silvia]

i said stiffness (large/small), not mass.