Temperature change effects on the mode shapes

[montazar]

Hi everyone

I am working on modeling a bridge in ABAQUS and I am interested in investigating effects of temperature change on the period of different bridge's vibration modes. Since I am new to the ABAQUS, I don't know what type of analysis should be used for that purpose. Any comments are welcomed.

Thanks a lot in advance for your help

Montazar

 

[Drej]

Structures at elevated temperature will typically reduce the modulus of the material and thus shift the eigenvaues down in the frequency spectrum. You can assess this effect by simply changing the modulus to reflect the modulus of the material at the temperature of interest. I would think that the temperature change would have to be fairly large to have a major affect on the modulus and hence the modes of the structure, and would expect practically that this wouldn't be a major issue. Probably.


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[montazar]

Thank you very much Drej

You are right but since the structure is constrained the change in temperature induces additional forces in the members which may change the period of bridge.
Anyway, forgetting about the modulus changes and supposing the temperature changes in the range 0 to +60 degrees do you have any idea about doing the analysis. I want to track the change of vibration mode periods along a typical day supposing I have the graph of the weather temperature change for 24 hours.

thanks
Montazar

 

[Drej]

This is not something that is straightforward to assess. But you can do a pre-stressed modal analysis to assess the bounds. First of all perform a steady state thermal stress analysis accounting for the temperature change and then use the results of this as the initial conditions for the eigenvalue analysis.


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[burningDiesel]

eigenvalue analysis is always a linear pertubation step. So at step 1 preload your structure (by temperature & constraints), at step 2 perform the eigenvalue analysis.
(This is the same as Drej said, only "use the results of this as the initial conditions" is a bit cryptic, you can just make a new step in abaqus)

 

[montazar]

Thanks a lot sdebock for sharing the information

But I think that only gives me the response at the final step, I mean I can't track the change in modes period as the temperature changes. I need to come up with graphs with horizontal axis to be temperature and the vertical one mode period. what you are saying only gives me the value of mode period at the final stage and the evolution of mode shape period cant be recorded.

Thanks again for your help

u of Alberta
Montazar