# I am unsure why my MATLAB code is causing errors and not matching hand calculations?

3 vues (au cours des 30 derniers jours)
Alex Soles le 14 Mar 2023
Commenté : Andreas Goser le 14 Mar 2023
Hand calculation is:
(125*25^3/12+125*25*(52.7-12.5))^2 + (15*160^3/12+15*160*(80+25-52.7))^2
ans = 2.7599e+13
= 16897581.42 or 1.69x10^7mm^4
MATLAB code error
% Dimensions of T-beam
T1 = 125; % Width of flange
T2 = 25; % Width of web
T3 = 160; % Thickness of flange
T4 = 15; % Height of web
T5 = 40; % Distance to K
% Compute the area and first moment of area for each rectangular section
A1 = T1*T2;
y1 = T2/2;
AM1 = A1*y1;
A2 = T3*T4;
y2 = T3/2;
AM2 = A2*y2+T2;
% Compute the total area and first moment of area
A = A1 + A2;
AM = AM1 + AM2;
% Compute the centroid location in the x & y direction
y_bar = ((A1*(y1))+(A2*((y2)+T2)))/((A1)+(A2));
x_bar = T1/2;
% Moment of Inertia
Ixx=((T1*T2^3)/12)+(A1*(y_bar-y1))^2+((T4*T3^3)/12)+(A2*(y2+T2-y_bar))^2;
fprintf('The Moment of Inertia is %s mm^4.\n',Ixx);
The Moment of Inertia is 3.153873e+10 mm^4.
Incorrect - should be 16897581 or 1.69x10^7 as per word calc? - Error in the main Moment of inertia code.
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### Réponses (1)

Andreas Goser le 14 Mar 2023
Could it be a need to write ".^2" rather than "^2"?
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Alex Soles le 14 Mar 2023
I have also tryed ".^3" and still have the same answer
Andreas Goser le 14 Mar 2023
Me recommendation is to make the comparison step-by-step so you can see in which calculation the issue occurs. It also helpt to share the full code again once you made an edit.
I just noticed the .^2 vs °2 as this can happen with beginnners. Also ./ vs. / is a frequent issue.

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