Standard Temperature Drop on Freezer Building 1

[Lily_Linton]

I have read a post about 2000kN tensile load on a temperature drop in warehouse. Thread was copied below for reference

https://www.eng-tips.com/viewthread.cfm?qid=341960...

Could anyone tell me how low does a temperature drop to consider this as part of the analysis?


Thanks!

 

[klaus.]

well ...basically tension load due to temperature is proportional to stiffness
so if you have a stiff element and this element is rigid fix at both sides rather high tension load can occur under temperature fall ...you can easily calculate by hand

 

[Lily_Linton]

Thanks klaus

I usually design for hotter temperature and added that as a load. Now if we're doing a freezer building although there's insulation, I wonder if 20 degrees Fahrenheit low needs to be part of the analysis or we can just follow the normal analysis

 

[ukbridge]

It depends on the support conditions - as Klaus said basically if you don't allow the member to expand/contract freely (i.e. rigidly fixed both sides) the force becomes "locked in".

To demonstrate this try setting up a frame model with extremely stiff columns and negligible beam stiffness and apply the temperature load. Conversely try the opposite and you'll find the tensile load will be far less.

For the temperature, it depends on whatever the client specifies i.e. what the temperature of the room will actually be + the usual safety factors. Other factors to think about is what temperature the beams will be when the steelworks erected i.e. reference temperature. After all you're really only interested in temperature difference not the actual temperature.

I'm not sure what you mean by the "normal analysis".

gl

 

[Lily_Linton]

Sorry for the confusion

What I mean about normal analysis is using the basic in loading, you know, wind, seismic, sdls,live loads, that sort, ignoring the temperature as part of the load. I'm in a tropical country so temperature was not that big thing in my department except if we are designing in middle east where we usually added 30degrees Celsius as part of our load.

Some oldies told me that we can ignore that temperature in analysis since it's higher than -50degrees but I want to know a different opinion about it

 

[ukbridge]

No worries, happy to help.

To be blunt, I would get the idea of a basic analysis out of your head - each non-trivial structure is its own characteristics and challenges. This especially applies to novel situations like this one you might be unfamiliar with.

To answer your questions:

1. No I dont think you should ignore the temperature by inspection. Heres why:

a) The structure is installed when the temperature is, say 25 degreesC given that its a hot country (Also known as the reference temperature).

b) The minimum design temperature of the structure in the freezer might be say, -20degreesC
(The client should help you define this temperature or by doing a bit of research). Common sense dictates we're not interested in expansion because we're in a freezer...

c) You calculate the temperature difference using T0 - Tmin (theres a bit more to it than that, but thats the general idea). Hence dT = 25 -(-20) = 45degrees.

d) You apply the temperature difference to your model and calculate bending moments, shears etc. You should also think about scenarios where the freezer might be turned off etc. If its a pure sway frame i.e. its allowed to flex there will be no locked in stresses, however this might not be the case as discussed in that thread you linked.

Also in a cold environment steel is much more brittle, and you should choose an appropriate subgrade with sufficient toughness.
Again thats something I'd be thinking about as an engineer that might not necessarily come from a code of practice.

2. I need more information but on first glance I would disagree with what they say about ignoring temperature since its higher than -50degrees. Again it all comes to context - ask them why..

As I explained earlier temperature effects (or rather the effects due to the temperature difference) depend on the actual structure, and how the beam/column/whatever is articulated. If you show me a sketch of what you're proposing I might be able to give you something a bit more concrete.

My (nagging) advice if you want to get better at structural engineering, get used to looking things at a first principles level.

Basically:

1. You have a structure you're designing.
2. You design it to the relevant design code in your country. The code should tell you how to calculate wind, seismic, temperature loads appropriate to your region.
3. You take into account the specifics - in this case the steelwork is in a (very) cold environment. Temperature is going to be different than that for an office or a bridge say. Exactly how much is up for you to find out (I'm not a freezers man admittedly, and if it'll have much of an effect depends on how the structure is articulated. This is what the code won't tell you and how we make our money at the end of the day!

If you have any more general questions, I'm happy to help.

best of luck