various temperature in shell element
various temperature in shell element
(OP)
Why the temperature are same in heat transfer analysis for depth of shell element? The integration point in slab was defined 5, Then I should have 5 different temperature.





RE: various temperature in shell element
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RE: various temperature in shell element
I have slab with fire in below level (not top). Then I defined heat flux in load from below surface.
with steady state I got no temperature variation but when I changed to transient it gave me different temperature.
But now question is I defined 20C for predefined in initial step. my steps is until 4860 second. In middle depth of slab I see temperature changes from 20C in 0 sec. and decreases to 18C and after that goes up. I think that the temperature should not be decreases !!!
I defined concrete with 2400 kg/m3 , specific heat: 900 and conv. 1.6 in SI
RE: various temperature in shell element
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RE: various temperature in shell element
1. I do not know, for 4 hours fire that temperature is varied by time, should I use STEADY STATE or TRANSIENT?
2. When I use STEADY STATE, the temperature in depth of concrete (250mm) is the same for all integration nodes (NT11,NT12,NT13,NT14,NT15)
3. Can I use shell element for 250mm concrete slab? I think YES
RE: various temperature in shell element
It's always wise to verify your answers by other means. Try a 1D model with lots of nodes through the thickness and compare the results with your shell model. Personally I wouldn't believe results of a transient thermal analysis from a shell model, but that's up to you.
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RE: various temperature in shell element
I think I should use steady state. Then why I have the same temperature in depth of shell element.
I defined 5 integration point in 250mm slab with shell element.I use surface heat flux in bottom surface of slab as a load.
In bindary condition I use a table with temperature variation from 20C to 1200C during 4860 sec. and NT11 is realease for temperature.
RE: various temperature in shell element
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RE: various temperature in shell element
My temperature must be varied with time from 20C to 1200C between 0 sec to 4860 sec.
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As I understand in your email: I must have transient (not steady state) because temperature is vary. OK?
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Temperature is from below of slab.
for heat flux (in load):
I put magnitude: 1 and amplitude: the default Instan... correct?
should I use bottom surface or top & bot.?
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RE: various temperature in shell element
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RE: various temperature in shell element
Heat flux is from top surface (Magnitude:1 Amplitude: Instantaneous)
But I see for NT14 and NT15 the temperature goes down and after goes up. NT11 shows correctly but NT14, NT15 not.
I attached my file (SLAB-HEAT TRANSFER model)
Thank you in advance
RE: various temperature in shell element
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RE: various temperature in shell element
The second model is for heat transfer (not first model)
My problem is for heat transfer model (second one).After it will be solved, I think the static model will be OK.
Please see the second model with name of SLAB-HEAT TRANSFER model.
Thanks again
RE: various temperature in shell element
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RE: various temperature in shell element
I changed 11 integration point instead of 5 points and now it is correct.
I checked the temperature output with hand calculation and SAFIR software and it is approximately OK.
Thanks again
RE: various temperature in shell element
I am trying to model something very similar to your discussion on various temp. in shell element for a research project. I looked at your slab model and I have a question regarding the rebar. As you know, you can not use rebar in heat transfer analysis. I see that you neglected it in this part of the model. However, you used it for the structural part. I am not sure how the model understands the degradation of the steel due to heat. Also, when I try to run the structural part of your model, I come up with an error that reads:
The number of temperature points 10 for beam or shell section found on the output database is larger than in the current model. This number must match between models.
Can you explain this error and how to avoid it?
Thank you so much for your help!