Creating a global stiffness matrix

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Rohit Raut
Rohit Raut on 9 Apr 2021
Commented: Yukthi S on 19 Apr 2024
I want to write a program to generate a 'global stiffness matrix of a 1 dimensional 2 noded n number of elements where the input will be coordinates of the nodes, area of cross section and Youngs modulus. I have written the following code but it has some errors. Please let me know how to proceed.
clc
clear
disp('Global Stiffness Matrix for a 2 noded 1-D element')
n=input('Enter the number of elements: ');
A=input('Enter the cross-sectional area of the element in mm^2: ');
E=input('Enter the Youngs Modulus of the element in N/mm^2: ');
for i=1:n
x(i)=input('Enter x coordinate');
y(i)=input('Enter y coordinate');
end
k=[1 -1;-1 1];
for i=1:n
k(i)=((A*E)/L(i))*k;
end
Kg=zeros(n+1);
for i=1:n
Kg(i:i+1,i:i+1)=Kg(i:i+1,i:i+1)+k(i);
end
disp('The global stiffness matrix is:')
Kg
  1 Comment
Yukthi S
Yukthi S on 19 Apr 2024
I see that you did not define "L" in the code. Assuming that "L" is the length of elements,I modifed the code. You can try it.
clc;
clear;
disp('Global Stiffness Matrix for a 2 noded 1-D element');
n = input('Enter the number of elements: ');
A = input('Enter the cross-sectional area of the element in mm^2: ');
E = input('Enter the Youngs Modulus of the element in N/mm^2: ');
% Initialize arrays for node coordinates
x = zeros(1, n+1); % Assuming linear elements, n+1 nodes
% Input node coordinates
for i = 1:n+1
x(i) = input(['Enter x coordinate of node ', num2str(i), ': ']);
end
% Initialize global stiffness matrix
Kg = zeros(n+1);
% Element stiffness matrix calculation and assembly into global matrix
for i = 1:n
% Length of the element
L = abs(x(i+1) - x(i));
% Local stiffness matrix for the current element
k_local = (A*E/L)*[1 -1; -1 1];
% Assembly into global stiffness matrix
Kg(i:i+1, i:i+1) = Kg(i:i+1, i:i+1) + k_local;
end
disp('The global stiffness matrix is:');
disp(Kg)

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