I've created little macro to compare the stress-strain relationship for different concrete models. The results for some models are not what I expected.
- Effective Height Reduction Factor doesn't work and Rec model looks like linear:
- Results for Par model are completely incorrect:
- If Exponent not equal to 2 and strain at the top is bigger then Strain Ultimate Limit, StrainToStress method return -1.#IND in Pow model (for strain bigger then the Strain Ultimate Limit). If Exponent equal to 2 (default value), results seems to be true:
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Roman Zhelezniak
Robot Evangelist & Passionate Civil Structural Engineer
Short resume after installing SP4:
Rec model - added warning message:
Par model - results are seems to be true:
Pow model - results should be close to Par model, now strain-stress relationship looks like:
Warning message has been added:
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Roman Zhelezniak
Robot Evangelist & Passionate Civil Structural Engineer
Dear Rafal, what you can say about Pow model?
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Roman Zhelezniak
Robot Evangelist & Passionate Civil Structural Engineer
I think that this part is missing (according to Eurocode 2 EN 1992-1-1:2004 p. 3.1.5 eq.3.14):
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Roman Zhelezniak
Robot Evangelist & Passionate Civil Structural Engineer
After installation of the Robot 2015 two different versions of rcuapi.dll were found.
Vesrsion 27.3.0.5135 by path:
c:\Program Files\Autodesk\Autodesk Robot Structural Analysis Professional 2015\RESC\RC\rcuapi.DLL
c:\Program Files\Autodesk\Autodesk Robot Structural Analysis Professional 2015\RESC\rcuapi.DLL
This version of rcuapi.dll can be succesfully registered and added as reference in VBA.
Vesrsion 28.0.1.5354 by path:
c:\Program Files\Autodesk\Autodesk Robot Structural Analysis Professional 2015\System\Exe\rcuapi.DLL
This version of rcuapi.dll after registration gives an error in VBA :
P.S. Is it possible to share what was modified/added in rcuapi.dll in the current version?
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Roman Zhelezniak
Robot Evangelist & Passionate Civil Structural Engineer
Ok, I found the reason of error from the previous post - Excel should be x64. But Spreadsheet Calculator works only with x32 Excel. I don't know how we can use those features simultaneously.
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Roman Zhelezniak
Robot Evangelist & Passionate Civil Structural Engineer
Results for the Par model became strange during the increasing of the design strenght:
30 MPa:
40 MPa:
70 MPa:
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Roman Zhelezniak
Robot Evangelist & Passionate Civil Structural Engineer
After the installation of SP2 for Robot 2015 results looks like:
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Roman Zhelezniak
Robot Evangelist & Passionate Civil Structural Engineer
Diagram is correct.
Your data is out of range data (regarding table 3.1) which should be used in formula 3.14
For your data : point in red circle becomes point in yellow one and then algorithm returns 0 as strain becasue strain is greater than eps_cu1
Let's return to concrete models.
Model Pow (from the help - Exponential relationship for non-linear structural analysis - Eurocode 2 EN 1992-1-1:2004 p. 3.1.5 eq.3.14. Atypical) is completly incorrect.
I've created own concrete model NonLin based on the above equation.
Function NonLinStress(eps_c, f_ck, E_cm, eps_c1, eps_cu1) 'Function describes stress-strain relation for structural analysis (EC2 f.3.14) 'eps_c - compressive strain in the concrete 'eps_c1 - strain at peak stress according to Table 3.1 'eps_cu1 - nominal ultimate strain 'f_ck - Characteristic compressive cylinder strength of concrete at 28 days 'E_cm - secant modulus of elasticity of concrete (according to Table 3.1 ???) eta = eps_c / eps_c1 f_cm = f_ck + 8 'mean value of concrete cylinder compressive strength [MPa] k = 1.1 * E_cm * eps_c1 / f_cm If eps_c = 0 Or eps_c < 0 Then NonLinStress = 0 If 0 < eps_c <= eps_cu1 Then NonLinStress = f_cm * ((k * eta - eta * eta) / (1 + (k - 2) * eta)) If eps_c > eps_cu1 Then NonLinStress = 0 NonLinStress = Round(NonLinStress, 2) End Function
Please find below comparison of results:
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Roman Zhelezniak
Robot Evangelist & Passionate Civil Structural Engineer
Hi @rsousa_ ,
The new version of this great dll was implemented in Robot 2021.
I hope @okapawal and @gwizdzm can give us more information.
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Roman Zhelezniak
Robot Evangelist & Passionate Civil Structural Engineer
Thank you @Romanich .
I don't have that version 😢. I'm digging this dll in visual studio (dll 64 bits and 32 bits office... ). It is super, but those errors are a mess... and it was phenomenal if you could set 2 types of steel for prestressing sections...
More information would be awesome.
kind regards
It seems that the BiLinear Rectangular concrete model does not work properly:
Expected results are shown in green:
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Roman Zhelezniak
Robot Evangelist & Passionate Civil Structural Engineer