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M
MB_124864925-Regular Member
5-Regular Member
December 3, 2024
Solved

Curve fitting - Creep Coefficient

  • December 3, 2024
  • 2 replies
  • 3884 views

I am trying to perform curve fitting using mathcad 13 to determine the best coefficients, "alpha" and "beta," that can approximate the equation of the three-parameter model (red line) to the creep equation according to Eurocode 2 (blue line).

 

MB_12486492_0-1733262357814.png

 



I cannot change the expression of the parameters in the three-parameter model equation. At this point, I have already tried using functions like "genfit."

MB_12486492_0-1733262553295.png        MB_12486492_1-1733262607485.png

However, the parameters I am finding are less accurate than those obtained using the trial-and-error method.

MB_12486492_2-1733263018399.png

I would greatly appreciate any help or suggestions you can provide.

Best answer by Werner_E

I am not sure but it may be hat you got confused about the time units?

 

Anyway, I just used your vectors X and Y and the function type you provided.
It looks to me that you had provided bad guess values.

But the function type seems not suit the data very well.

There may be other function types better suited. Some examples see below

Werner_E_0-1733284853205.png

 

 

2 replies

W
Werner_E25-Diamond IAnswer
25-Diamond I
December 4, 2024

I am not sure but it may be hat you got confused about the time units?

 

Anyway, I just used your vectors X and Y and the function type you provided.
It looks to me that you had provided bad guess values.

But the function type seems not suit the data very well.

There may be other function types better suited. Some examples see below

Werner_E_0-1733284853205.png

 

 

M
MB_124864925-Regular MemberAuthor
5-Regular Member
December 4, 2024

Thank you very much for your attention, Mr. Werner.

 

I have reviewed your solution; however, I am unable to open the file in my version of Mathcad (version 13.0).

 

MB_12486492_0-1733316099322.png  

 

Would it be possible to convert the file to a compatible format?

 

I appreciate your assistance.

W
Werner_E25-Diamond I
25-Diamond I
December 4, 2024

Would it be possible to convert the file to a compatible format?

Sure! Fortunately we are using real Mathcad here and not Prime. So its possible to save back in an older version format without problems.

Attached is the file in MC13 format but he pictures in my last post already showed it all, nothing hidden 😉

 

In future question please state which version of the software you are using.

L
LucMeekes23-Emerald IV
23-Emerald IV
December 4, 2024

Bom dia,

I fail to see the point of curve fitting. Following your sheet I find:

LucMeekes_0-1733348471545.png

that define:

LucMeekes_1-1733348490428.png

and:

LucMeekes_2-1733348510792.png

that define:

LucMeekes_3-1733348530077.png

to finally define:

LucMeekes_4-1733348546215.png

So the function you are trying to approximate is actually

LucMeekes_5-1733348597014.png

With the values:

LucMeekes_6-1733348639704.png

this plots as:

LucMeekes_8-1733348707437.png

So the shape of your function is determined with only four parameters.

Why settle for less accurate results in two or three parameters?

 

Success!
Luc

 

M
MB_124864925-Regular MemberAuthor
5-Regular Member
December 6, 2024

Hi Mr. Luc Meeks,

 

I truly appreciate your attention to my question and your opinion.

 

Indeed, the creep coefficient depends on many factors, such as the age of the concrete at the time of load application, curing conditions, environmental factors like relative humidity, the level of applied stress, the duration and history of loading, the dimensions of the concrete elements, the material composition, and other factors.

 

I am attempting to simplify this by using an equation that depends on the modulus of elasticity and the viscosity modulus of the concrete.  While it may not achieve 100% precision, will provide a good level of accuracy.

 

I am attaching an article containing parts of my research, where the next step involves refining this curve as accurately as possible using a programming routine.

 

Any criticism, considerations, or suggestions are always welcome.

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