load transfer

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isolator
Posts: 20
Joined: Tue Apr 02, 2013 12:35 am

load transfer

Post by 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
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Re: load transfer

Post by 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
Posts: 20
Joined: Tue Apr 02, 2013 12:35 am

Re: load transfer

Post by isolator »

Thanks for you reply!
shenxian
Posts: 25
Joined: Tue Aug 14, 2012 5:52 pm
Location: Shijiazhuang tiedao University

Re: load transfer

Post by shenxian »

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

Post by 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
Posts: 25
Joined: Tue Aug 14, 2012 5:52 pm
Location: Shijiazhuang tiedao University

Re: load transfer

Post by shenxian »

thanks for you reply,fmk.
isolator
Posts: 20
Joined: Tue Apr 02, 2013 12:35 am

Re: load transfer

Post by 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
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Re: load transfer

Post by 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
Posts: 20
Joined: Tue Apr 02, 2013 12:35 am

Re: load transfer

Post by 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
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Re: load transfer

Post by 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
}
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