Discrepancy in Ixx value in composite section for construction stage and how does midas calculates notional size of a section? 

Question:

1. I am using the Composite Section for Construction Stage. When I check the composite stiffness values from this tab I notice that the Ixx (torsion) is not correctly calculated for the composite section. I compare this to the value directly from Section Data results. See screenshots below. 

This is quite a difference and affects results a lot. Can you please explain the difference as I believe the correct value is the Section Data but this is not what the analysis uses. 

Figure above from Composite Section for Construction Stage


Figure above from Section Data

2. Secondly since there is this limitation how does it apply to the notional size of member 'h'. The values of h suggest they are for each part 1 and 2 independently. How does the software then calculate 'h' of the composite section? Before composite the girder part 1 has entire perimeter exposed however once composite part 1 and 2 combined there is now an internal void which changes the calculation for perimeter and hence 'h'.
Thanks

Answer:


1. The screenshot was taken from the online help manual. refer the online manual shown below which has question 1. Click here for the link to the question.



2.  Yes, the notional size is calculated/entered as part wise independently. 
As the different parts of the composite has different age, therefore, the separate notional size for each part is calculated to obtain creep and shrinkage.
Further, the general practice is that, for part 1, h is manually calculated and entered as per enclosed section as the for most of it's service life it remains enclosed.
The midas will auto-calculate the h value of each section independently without considering it enclosed section. So, for enclosed section part, we need to update the value of h manually.




REQUESTION:(Q3)
Secondly since there is this limitation how does it apply to the notional size of member 'h'. The values of h suggest they are for each part 1 and 2 independently. How does the software then calculate 'h' of the composite section? Before composite the girder part 1 has entire perimeter exposed however once composite part 1 and 2 combined there is now an internal void which changes the calculation for perimeter and hence 'h'. 







Answer 3
Actually, currently it is limitation of the software.

So, workaround for this is giving the section stiffness scale factor as shown below. Enter the appropriate section stiffness scale factor for Ixx only.


Hope this helps and kindly let me know if further assistance is required.
Creation date: 6/8/2021 2:12 PM      Updated: 5/3/2023 5:49 PM
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