How to create a combination that meets the requirements of EN1340 12.3.4-2, Tau 4, Press and Moments for Sustain +Resultant moments from Thermal expansion using AutoPIPE?
Would this be correct?
AutoPIPE supports the use of equation 12.3.4-2 of EN13480 using sustained margin calculations. This is explained in the ‘Use min. sustained margin’ help page. This page is linked at the bottom of the ‘Thermal Expansion Stress Range’ page for EN13480 (Reference Information>Code Compliance Calculations>EURO EN 13480 (2017)>Thermal Expansion Stress Range (EN13480 – 2017)).
The sustain margin calculations should meet the requirements of the equation for thermal loads as stated in the help page:
Here, the equation 12.3.4-2 is followed when sustain margin is used to calculate thermal allowable stresses. Rearranging the equation highlighted above, and substituting the SL variable with the sustained stress, we get the following:
Rearranging, we would get equation 12.3.4-2 as follows:
Using the sustained margin, there should be no need to manually recreate equation 12.3.4-2 with user defined combinations since the sustained loading has already been taken into account when reporting the thermal allowable stress.
If users still want to add the sustained and thermal stresses in a single combination, they will need to face several limitations such as manually entering the thermal allowable stress for each combination. If this is required, the following steps would help:
Create a user defined combination with the combination method set to ‘Sum’ and category set to ‘Expan’. Add the required nested sustained and thermal combinations at the stress level to this combination as follows: This combination should give the correct calculated stress according to equation 12.3.4-2.
The correct allowable stress would need to be set up manually by the user. The steps to do so are as follows:
- Since adding the sustain margin gives a different thermal allowable than the required (ff + fa) allowable given in equation 12.3.4-2, users would need to disable sustain margin from being added. This can be done by setting the ‘Sustain margin [Y/N/E]’ field in the result model options to ‘N’.
- Users would need to manually add the thermal and sustained allowable stress values (ff + fa) for the material used, and assign them to the user defined ‘SUS + EXPANSION’ combination through the ‘Allowable Stress’ column in the load combination dialog:
The steps given above correctly calculate the stress and allowable stress values required by equation 12.3.4-2. The allowable stress value, however, would change depending on the temperature and material used. Hence, if users have different materials being used in the same model, they will need to define new combinations for each material used with the correct thermal allowable (ff + fa) value assigned to the combination as follows:
En13480 Piping calculations