Question about modeling SDOF structures having its T,Sa &...

[omidgahremani]

How could I model a single degree of freedom structure with only having it's Period, yield acceleration and ductility in opensees.
notice I don't have any section's or node's or element, and all I have is the previously mentioned characteristic's .
P.S : my model's are 2D .

[fmk]

you can't directly .. it would have to be a spring model with some ElasticPP material, you could come up with all properties but the yield point for the material. then you would have to run through different values of yield value to see what the effects are on ductility and yield acceleration for the excitation you have. there are some general rules of thumb for ductility

[omidgahremani]

thank you for your help.
I'm using this model for doing IDA analysis, Does it help in this process ?

[fmk]

lots of people use OpenSees to do IDA's, but they have a model to start with, i.e. for a SDOF elastic-plastic system they already have a mass, a stiffness and yield point. from your original question, you do not have these. maybe you should talk to the person who gave you this to make sure you know what it is they want.

[omidgahremani]

Dear fmk
I considered your answer carefully. I will assume a mass for this model and hence the stiffness can be calculated for it.
the question is can I use the yield acceleration as yield point in spring model with some ElasticPP material that you mentioned before?

[fmk]

you cannot use the yield acceleration as a parameter to define the ElasticPP material, the material knows nothing about the acceleration (all it sees are the strains).

as mentioned in the second post you are just going to have to do a lot of analysis changing the parameters.

[yuanzhenwei]

Have you solve your problem？I am a beginner in opensees，I met the same problem with you. I need to model a single degree of freedom structure for doing IDA analysis,but now I haven't solve the problem , Whether can you give me the code ? We can communicate with each other through the mail , my email is hit-yzw@outlook.com . thank you very much !

[omidgahremani]

yuanzhenwei wrote:
> Have you solve your problem？I am a beginner in opensees，I met the same
> problem with you. I need to model a single degree of freedom structure for
> doing IDA analysis,but now I haven't solve the problem , Whether can you
> give me the code ? We can communicate with each other through the mail ,
> my email is hit-yzw@outlook.com . thank you very much !

Hi,
Use something like this :
___________________________________________
# Model for SDOF system
model BasicBuilder -ndm 3 -ndf 6
#Nodes, restraints, material end element
node 1 0.0 0.0 0.0
node 2 0.0 0.0 0.0 -mass 4.446e+02 0.0 0.0 0.0 0.0 0.0
fix 1 1 1 1 1 1 1
fix 2 0 1 1 1 1 1
# uniaxialMaterial Hysteretic $matTag $s1p $e1p $s2p $e2p <$s3p $e3p> $s1n $e1n $s2n $e2n <$s3n $e3n> $pinchX $pinchY $damage1 $damage2 <$beta>
uniaxialMaterial Hysteretic 1 2.764e+03 2.516e-02 2.764e+03 1.583e-01 8.419e-03 4.700e-01 -2.764e+03 -2.516e-02 -2.764e+03 -1.583e-01 -8.419e-03 -4.700e-01 0.000e+00 0.000e+00 0.000e+00 0.000e+00 8.000e-01
# section Aggregator $secTag $matTag1 $dof1 $matTag2 $dof2 ....... <-section $sectionTag>
section Aggregator 1 1 P
# element zeroLengthSection $eleTag $iNode $jNode $secTag <-orient $x1 $x2 $x3 $yp1 $yp2 $yp3> <-doRayleigh $rFlag>
element zeroLengthSection 1 1 2 1
_____________________________________
best regards,