Hi,
from: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/6191/ram-concept-load-history-calc-options-tn
the first screen shot of the Cal Options noted that ECR fields are only applicable to ACi209R-92. So does it means if I am using AS3600-2018, I do not need to change ECR fields? If this is the case why having different ECR\creep factor value under AS3600-2018, I get slightly different deflection value (less than 1-2mm)? I was expecting identical Sustained Load plan.
Thanks
There were 2 changes made to the load history deflection analysis in v8.2 that could produced different results with the ACI 209R-92 model:
1) RAM Concept uses the Eurocode 2 tension stiffening model for all implemented models. That tension stiffening utilizes a Beta parameter, which Eurocode 2 states should be taken as 1 for short-term loading and 0.5 for long-term loading (see Clause 7.4.3). In previous versions, Beta = 1 was used. In the current version, Beta = 0.5 is used. See the section titled "Load History Tension Stiffening Model" in the release notes linked below for more discussion on why that change was made.
2) Adjustments for early-age concrete strength are now accounted for by the program. This change can affect both creep calculations and the modulus of rupture (cracking). See the section titled "Load History Calculations - Strength Adjustments for Time of Loading ACI209R-92 Creep/Shrinkage Model" in the release notes for more discussion on this change.
https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/52277/ram-concept-connect-edition-v8-update-2-release-notes
Hi Karl,
I am confused why is it that first screen shot from https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/6191/ram-concept-load-history-calc-options-tn :
is saying the ECR fields "Used Only for ACI209-92....", yet if I used AS3600-2018 for Creep/Shrinkage model , and if i input different Creep factor under ECR fields, I would get different answer when I looked at the Sustained Load deflection plot?
If you have AS 3600-2018 selected for the creep and shrinkage model, then the values in the ECR field should have no effect (assuming that the selected design code also was not changed). If you are seeing a change in deflections when changing those values with the AS 3600-2018 model selected, please share your model using the Secure File Upload so we can review. Please post the file name here after is uploaded.
hi Karl,
I've uploaded the file.
I would like to correct myself, I can only see less than 1mm different (I may have adjusted other variables when I saw 1-2mm different).
This is a preemptive comment: I don't think Bentley should gray out ECR fields when user not selecting ACI for Creep/Shrinkage model.
We are still reviewing this. However, we have confirmed that difference does not result from different creep coefficients or shrinkage strains. When comparing the results between the models, there are a few cross section that show slightly different results, but the creep coefficients and shrinkage values for those sections are exactly the same.
This points to a convergence issue with the iterative load history analysis as the cause of the difference. We will need more time to review the models to understand where and why the results for the few cross sections are diverging.
We cannot gray out the ECR box when the other creep/shrinkage model are selected, because the ECR value is calculated during the main calculations and has uses outside the load history analysis.