Temperature load in STAAD (Thermal load of steel )

Question

Dear Engineers, 
 Im analysing a steel structure where I have to apply thermal load. below are the datas. 
 
 Max. Temp 45 deg Celsius 
 Min.Temp -35 deg Celsius 
 Site Average maximum temperature : 36&deg;C 
 Site Average minimum temperature : -22&deg;C 
 
 In STAAD we have below 3 things in the input cell. How to calculate this from the above input. 
 Temperature Change for Axial Elongation 
 Temperature Differential from Top to Bottom 
 Temperature Differential from side to side

DSANJU · Answer

You have to know three temperatures : 
 
1) the stress-free temperature, which is the temperature that the beam was at when it was constructed or installed. Call it A. 
 
2) The temperature of the top fiber (the fiber that is farthest along the positive direction of the local Y axis). Call it B. 
 
3) The temperature of the bottom fiber (the fiber that is farthest along the negative direction of the local Y axis). Call it C.

When you specify the temperature load, the command is

member-list TEMPERATURE f1 f2 
 
where 
 
f1 = (B+C)/2 - A 
 
f2 = B-C

Rajat · Answer

You can also refer the following post where the same is discussed:- 
 http://communities.bentley.com/products/structural/structural_analysis___design/f/5932/t/86174 
 Thank you.

Rajat · Answer

Since the stress is caused on the structure by a change in temperature, knowing the maximum and minimum temperatures alone is not enough. You need to know the average temperature at which the structure was built, which is called the stress free temperature (temperature at which the structure is not undergoing any stress due to the thermal condition). The change in temperature from that stress-free temperature is what the program needs to know. 
 
 As you say, the entire beam undergoes a temperature change. There are 3 points where that is measured - top fiber, centroid, and bottom fiber. That increase causes two effects - axial elongation/contraction, and bending. The axial elongation/contraction is handled thru the term f1 in our earlier answer. The bending effect is handled using f2.

Kris Sathia · Answer

f1 as +18 in one load case, and, -62 in another load case, is correct. 
 
Do not take the average of Max and Min.

Kris Sathia · Answer

We are not aware of any mistake in STAAD when it comes to temperature load analysis. It has been used on hundreds of models by practicing engineers for the past 15-20 years, and our developers have reviewed it in detail on several occasions over the years. There are also a number of validation examples that it has been checked against. 
 
Temperature loads produce very high stresses. If you don't want the members to experience such stresses, your connections could be designed as slip joints which will enable expansion or contraction of the members and relieve the thermal stresses. You could model such connections in the analysis by releasing FX at one end of such members. 
 
I will have a look at your latest models as soon as I can find some time.