In the manual it says that according to ACI average final creep factor is 3.35 which is different for AS3600 where creep for F'c 40 MPa 200 thick slab in temperate environment is 2.23. The difference is quite high and approach to calculate deflections according these 2 standards would be different.
Which approach is taken in the software in order to account for long term deflections according to AS3600?
You may find the following web page helpful:
http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/6191.ram-concept-load-history-calc-options-tn.aspx
The ACI 209 creep model is used to account for creep for all design codes, including AS3600. ACI 209 assumes that the initial loading is applied at 7 days. AS 3600 assumes a different time for initial load application, so the creep factor must be adjusted for an initial loading time of 7 days when that design code is selected.
You are correct that using the AS3600 adjusted creep factors may be significantly different than the suggested creep factors in ACI 209. Also, RAM Concept may be using slightly different values at times other than the ultimate creep due to using a curve from a different creep model. However, RAM Concept is ultimately using input values that are required by AS3600 and those values should be input into the program.
Answer Verified By: VBWGE
Thanks
Thanks for the guidance.
However can you please elaborate on your final paragraph? How should Australian designers go about adjusting the Creep Coefficient & Shrinkage Strain?
Does ACI use something similar to AS3600's Theoretical Thickness (th)?
AS3600 assumes initial loading @ 28 days, how can this be accounted for in the creep coefficient?
I'm paraphrasing something from the Ram Concept development manager, but this seems to fit your situation:
Question: "Could you please confirm what we would be using as the value for Creep Factor in the Calc Options menu input. We design to AS3600. Should we use the Basic Creep Co-efficient from Table 3.1.8.2 of AS3600 or should we use the Final Creep Co-efficient (after 30years) value from Table 3.1.8.3."
Answer: RAM Concept works out the fraction of creep that occurs in any time period, and also modifies the input creep factor for time of application of loading (in the AS code, the “maturity coefficient”). However, all other effects are meant to be factored into the input creep factor. That would indicate that the values from Table 3.1.8.3 should be used – however, note that those values are for concrete loaded at 28 days, and ACI 209 which RAM Concept uses is based upon loading at 7 days. Therefore, all creep values input into RAM Concept should always be for initial loading time at 7 days.
Thus, the values should be taken from Table 3.1.8.3, but then multiplied by the k3 modifier of 1.75/1.1 = 1.59.
One other recommendation we’ve made to people is to pick the time of interest they are attempting to calculate, and calculate the final creep coefficient including all effects at that time. Then, using the ACI 209 models back calculate the effective equivalent ACI 209 creep coefficient and input that into Concept. That approach will give an answer –at that instant in time – very close to that as if the AS 3600 creep model was actually implemented in Concept.
Thanks for clearing a few things up Seth.
How would you recommend we go about taking into account the hypothetical thickness?
Better yet, are there plans to implement a code specific (As3600) creep model for use in Concept?