load transfer

[isolator]

I have two questions.
First,when defining gravity load,the superstructure and the pier's dead weight are defined,the load that the superstructure transfer to pier is defined or not?OS can transfer load automatically?
Second,does the modal analysis add gravity analysis?

[fmk]

not quite sure what you are asking in the first part. if you are saying that you have added element or nodal loads to the superstructure and are the loads transmitted to the piers, the answer is yes if you have performed a static analysis. you should see this if you look at element forces or reactions after the analysis.

in your second question: OpenSees does not do "modal analysis". it will determine the eigen values or will allow you to perform a full transient analysis. if you perform the transient analysis after the gravity analysis and do not remove the gravity loads, then yes of course the loads are included. just make sure they are made constant afte the end of the gravity.
see the examples:

http://opensees.berkeley.edu/wiki/index ... e_Analysis

[isolator]

Thanks for you reply!

[shenxian]

Hi. fmk .I have a question.
Whether or not opensees can do "modal analysis " ? Can you sayit in detail.

[fmk]

sorry, but i have 2 answers for you.

no. there is no built-in command to do 'modal transient analysis'. There is no 'analysis ModalTransient', only 'analysis Transient'. This latter transient analysis performs the analysis in the numerically correct way (especially for nonlinear models). we don't leave out any modes nor do we combine the results in approximate ways.

and yes. if you want to do modal analysis you can to do it in the scripts using the eigenvalues and mode shapes determined from issuing the 'eigen' command. here is an example:

http://opensees.berkeley.edu/community/ ... 1396#p1396

[shenxian]

thanks for you reply,fmk.

[isolator]

hello,fmk!
when i output the eigenvalues,LRB bearing is a bi-linear material,i want to use the post-stiffness to obtain the eigenvalues,how can i achieve
it? i use "element elastomericBearing" to simulate the bearing.

[fmk]

if you want the eigenvalues for the latter (and the rest of the model is elastic), just do a run with an elastic material with the stifness you want.
otherwise, as you can issue an eigen command at every step in the analysis if you want, do multiple eiegen analysis,.

[isolator]

thanks for your reply!may i do this in this way:i use "uniaxialMaterial Elastic" command to give the post-stiffness value ,then i use "element zeroLength" instead of "element elastomericBearing",add the material to the zeroLength element.is it right?
"as you can issue an eigen command at every step in the analysis if you want, do multiple eiegen analysis" What is the meaning of this?

[fmk]

the latter is simple, obtain and write the eigenvalues at every step:

set count 0
while {$count < $numStep} {
analyze 1 $dt
set eigenvalues [eigen $numMode]
set time[getTime]
puts $eigenFile "$time $eigenvalues"
incr count 1
}