Hello CEE, What a treat, the CEE channel is on fire (pun intended) this weekend, thank you so much for the weekend videos that are shared so far. Pardon my ignorance, I am still unclear with regard to the idea behind what we are actually doing when we say that we are “Designing for fire” - What are we doing in simple terms? - Are we simply creating a “load combination with dead load and a reduced live load”? - Comparing to earthquake (seismic) design, the earthquake parameters resolve to lateral forces that are applied directly to a structure. Do the fire analysis parameters resolve to some form of “equivalent forces” that are applied to the structure? OR - OR, do fire analysis parameters work in more or less the same way as say buckling and torsional buckling parameters which instead results in reduced effective lengths and reduced critical stresses in a member that would reduce the stresses at which a member would be considered to be passed? - Or both (load combination, and reduced member resistance properties) is the resulting effects of checking or of designing a member for fire? How is temperature load case in a structure related to or influence the “Designing for fire” ? will a fire combination automatically include a “temperature load case” if there is a temperature load case that is defined in a structure? Thank you for this short video, it helps to explore these infrequently explored areas of structural design. I have enjoyed the video and I am looking forward to the next CEE videos Regards, DK
Hi there Engr. DK ^_^ Happy you liked the video. As far as I know, both approaches exist. On the one hand, fire is dealt with as a "reduction in the load carrying capacity" of structural elements, as an increase in temperature usually has an adverse effect on the yielding of steel and crushing of concrete as well as other negative effects like spalling of concrete, so one point of understanding is that it is a reduction of the capacity with time. In my humble opinion - however - and that is what the Editor correctly mentioned, I still wanted to say that there might be a need to define temperature loads on the structure. The fire combination was done according to the load, I was personally surprised that it considered the live load reduced - at first -. But upon further thought it made sense as people would tend to evacuate the building, with exception to some few poor souls and the furniture that is not going to be evacuated. So, as far as I know, the Eurocode's approach (general) is to define a temperature curve and calculate: E,d,fi = factor * E,d where E,d is the design load level, which is reduced to account for fi = fire. Here is a quick - but not extensive - reference to check: eurocodes.jrc.ec.europa.eu/sites/default/files/2022-06/02-CALGARO-EC-FireDesign-WS.pdf Of course, this leaves the question of temperature load still to be asked. We know that for an indeterminate structure, loads due to temperature will have an effect on the internal loads of members. Now since the EC has so many National Annex, I wanted to give a disclaimer in the video that maybe (I am not really sure), one national annex would require to apply a certain temperature change on certain elements to check for failures. That was the reason why. Ok, so what are we doing (what is happening in this specific video?) We are creating Fire load combinations, which are basically load combinations generated from your original load cases such as dead and live. We then define what kind of fire we are expecting the element to endure, and the duration and all the parameters necessary. This would come into play when calculating a "reduced resistance". Note that: the resistance here is a function of time, and that is the reason why one input is "the time of fire" in the parameters, as robot will calculate the resistance at that time and compare it with the loads. You are right if you think now that: well if I say 30 mins, then the structure is safe only for 30 mins, and may collapse after that. Yes, you are right, and that is a decision to be taken in accordance to code. A one story structure has more relaxed evacuation times than say: a high rise building. Then we switch on the fire design in the configuration of the design GUI in robot. Hope this explanation made more sense. Regards, CEE
Dear Prof. C E E, Thank you very much for your sharing. one suggestion if you can separate VDO for steel warehouse design member parameter in to AISC code it's really good ❤ .
I am really happy you liked it. I think this would be a good idea, I will see if I can somehow cover it quickly, If I cannot, well, you have all the necessary tools to deal with it Still, stay tuned for more content. Regards, CEE
Hello, What are your thoughts about calculating ULS for C-profiles in Robot (especially lateral buckling)? Some people say that Robot calculates it incorrectly and therefore Mcr value is also incorrect. What is your approach for such case?
Hi there, As far as I know, Cold-Formed C channels are not covered in American codes at RSA at the moment, as the AISC is covering hot rolled sections. For the Hor rolled C-Channels, I have to personally investigate it. I will definitely check it out and get back to you with that regard. Regards, CEE
Dear CEE thank you very much for this video, i have a question, can you use time-temperature parametric curves for “realistic” fire approach as EC1? Again this channel is going to be where everybody goes to learn how to deal with RSAP and structures!
Hi there Engr. Candea, Happy you like those videos ^_^. If I understood your question, by realistic fire you mean the "temperature curve" that can be selected in robot. If that was the question, it is unfortunate to say that I have not been able to find a way to input those curves manually. I am going to send an email to the RSA team just to make sure I am not missing anything. Still, stay tuned for more content. Regards, CEE
Hello CEE,
What a treat, the CEE channel is on fire (pun intended) this weekend, thank you so much for the weekend videos that are shared so far.
Pardon my ignorance, I am still unclear with regard to the idea behind what we are actually doing when we say that we are “Designing for fire”
- What are we doing in simple terms?
- Are we simply creating a “load combination with dead load and a reduced live load”?
- Comparing to earthquake (seismic) design, the earthquake parameters resolve to lateral forces that are applied directly to
a structure. Do the fire analysis parameters resolve to some form of “equivalent forces” that are applied to the structure?
OR
- OR, do fire analysis parameters work in more or less the same way as say buckling and torsional buckling parameters
which instead results in reduced effective lengths and reduced critical stresses in a member that would reduce the
stresses at which a member would be considered to be passed?
- Or both (load combination, and reduced member resistance properties) is the resulting effects of checking or of
designing a member for fire?
How is temperature load case in a structure related to or influence the “Designing for fire” ? will a fire combination automatically include a “temperature load case” if there is a temperature load case that is defined in a structure?
Thank you for this short video, it helps to explore these infrequently explored areas of structural design.
I have enjoyed the video and I am looking forward to the next CEE videos
Regards, DK
Hi there Engr. DK ^_^
Happy you liked the video.
As far as I know, both approaches exist. On the one hand, fire is dealt with as a "reduction in the load carrying capacity" of structural elements, as an increase in temperature usually has an adverse effect on the yielding of steel and crushing of concrete as well as other negative effects like spalling of concrete, so one point of understanding is that it is a reduction of the capacity with time.
In my humble opinion - however - and that is what the Editor correctly mentioned, I still wanted to say that there might be a need to define temperature loads on the structure. The fire combination was done according to the load, I was personally surprised that it considered the live load reduced - at first -. But upon further thought it made sense as people would tend to evacuate the building, with exception to some few poor souls and the furniture that is not going to be evacuated.
So, as far as I know, the Eurocode's approach (general) is to define a temperature curve and calculate:
E,d,fi = factor * E,d
where E,d is the design load level, which is reduced to account for fi = fire.
Here is a quick - but not extensive - reference to check:
eurocodes.jrc.ec.europa.eu/sites/default/files/2022-06/02-CALGARO-EC-FireDesign-WS.pdf
Of course, this leaves the question of temperature load still to be asked. We know that for an indeterminate structure, loads due to temperature will have an effect on the internal loads of members. Now since the EC has so many National Annex, I wanted to give a disclaimer in the video that maybe (I am not really sure), one national annex would require to apply a certain temperature change on certain elements to check for failures. That was the reason why.
Ok, so what are we doing (what is happening in this specific video?)
We are creating Fire load combinations, which are basically load combinations generated from your original load cases such as dead and live.
We then define what kind of fire we are expecting the element to endure, and the duration and all the parameters necessary. This would come into play when calculating a "reduced resistance". Note that: the resistance here is a function of time, and that is the reason why one input is "the time of fire" in the parameters, as robot will calculate the resistance at that time and compare it with the loads.
You are right if you think now that: well if I say 30 mins, then the structure is safe only for 30 mins, and may collapse after that. Yes, you are right, and that is a decision to be taken in accordance to code. A one story structure has more relaxed evacuation times than say: a high rise building.
Then we switch on the fire design in the configuration of the design GUI in robot.
Hope this explanation made more sense.
Regards,
CEE
@@CivilEngineeringEssentials
The explanation is perfect, thank you and thank you for the reference.
Regards, DK
Dear Prof. C E E, Thank you very much for your sharing. one suggestion if you can separate VDO for steel warehouse design member parameter in to AISC code it's really good ❤ .
I am really happy you liked it.
I think this would be a good idea, I will see if I can somehow cover it quickly,
If I cannot, well, you have all the necessary tools to deal with it
Still, stay tuned for more content.
Regards,
CEE
Hello,
What are your thoughts about calculating ULS for C-profiles in Robot (especially lateral buckling)? Some people say that Robot calculates it incorrectly and therefore Mcr value is also incorrect. What is your approach for such case?
Hi there,
As far as I know, Cold-Formed C channels are not covered in American codes at RSA at the moment, as the AISC is covering hot rolled sections.
For the Hor rolled C-Channels, I have to personally investigate it. I will definitely check it out and get back to you with that regard.
Regards,
CEE
Dear CEE thank you very much for this video, i have a question, can you use time-temperature parametric curves for “realistic” fire approach as EC1? Again this channel is going to be where everybody goes to learn how to deal with RSAP and structures!
Hi there Engr. Candea,
Happy you like those videos ^_^.
If I understood your question, by realistic fire you mean the "temperature curve" that can be selected in robot. If that was the question, it is unfortunate to say that I have not been able to find a way to input those curves manually. I am going to send an email to the RSA team just to make sure I am not missing anything.
Still, stay tuned for more content.
Regards,
CEE