i have modeled the RC beam with simply supported BC and used concrete smeared cracking to account for the nonlinearities in concrete, i have got the frequency value for the case of beam under its own weight only, i want to add loads to it to get values of frequencies for cases.
i have used a static general step to define the added load, knowing that this step is before the frequency step, but the results of frequency are just the same!
i'm still just a beginner on ABAQUS, can you guys help?
is it possible to change the material properties and a way of model solution ?
i think the load or frequency you want to add to your model not connected with your solution...
can you change it ?
which of model solution you choose ? what is the concrete cracking model ?
hello dear friend
i can help you. it is easy to model the RC structures
you can find your answer in youtube and books and papers.
but the same results appears from many reasons. check the interactions, loads, boundary condition if they are ok after that you should check your model?
did you Verify your model ?
you should modeled your own work based on reliable paper...
First of all thank you for answering :)
Yeah i have verified the value of the frequency that i have got from my model compared with a value from a paper work, but this model was under beam self weight only, the problem is when i add the load, the frequency should change according to the change in beam stiffness that is caused by cracks in concrete, noting i have used concrete smeared cracking in the material section to accout for these cracks.
The load i add was used in a general static step before the frequency step, because it is static, and this would consider it as a base for the next step(frequency).
Do you think that there is a problem in connecting these steps? or you think there's a problem in the "concrete smeared cracking" model, it should consider stiffness change according to addition of load, right?
is it possible to change the material properties and a way of model solution ?
i think the load or frequency you want to add to your model not connected with your solution...
can you change it ?
which of model solution you choose ? what is the concrete cracking model ?
hi
how did you apply self weight?
which frequency you are interested (free vibration or forced vibration)
hello friends, thank you for your responses :)
absolutely Arash, my load step which is "General static" is not connected with the frequency step, i can't define the load in the frequency step, it has to be in a different step before.
in literature, what causes the frequency to change is the change in concrete stiffness because of the cracks, i have modeled the concrete plasticity as smeared cracking model in ABAQUS which uses the plastic strain vs compressive stress diagram , failure ratios and tension stiffening , do you think these properties are enough to model the change in concrete stiffness with the cracks? my question here is ,could the problem be in the material definition?
Raafat, i have applied the load as a pressure and as a point load on the beam using a static general step, this step is used as a base step for the frequency step, i'm interested in both free vibration and forced vibration by moving load , but i'm interested in the free vibration at this stage.
Regards
i think but not sure that your model frequency is high so the frequency load you apply to your model is very little in comparing with your model natural frequency.
increase your frequency and compare your model...
or
before you do the past order I recommend to you. at first find your natural frequency of your model.
if you know it the frequency load you apply to your model is appear and you know how much you want to apply...
if it wont give you answer
send your model to my email address to investigate what did you do . . .
Best Regards
hi
regarding to your question about concrete model that can consider cracking, yes there is another model provided by abaqus called concrete damage plasticity (CDP) which needs definition of stress-strain table for compressive behavior and the corresponding damage table and similar tables are needed for tensile behavior. Also it needs some parameter which should be calibrated with experiment results of your considered RC beam. if you need excel sheet to generate these tables for any ultimate concrete strength, please let me know and I will send you on your researchgate mail.
regarding to frequency, I noticed that you have received good advice from Mr Arash that need you to try it frist
good luck
thank you both for your answers.
Mr Raafat, i have tried using the CDP model! it really works, i discovered it's better to use for dynamic loads! didn't know this
anyway, could you send me that excel sheet that would help me to generate the CDP tables? i really need it
Regards
hi Yasmeen
i wil send you what i have so far although i am working with another stress strain curve and when i finished i will send it to you too. just give me two more dayes cause i am a little bit busy with corrections
best regards
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