# the global stiffness of two 4x4 matrices of truss

2 views (last 30 days)
Commented: Mohammad on 22 Sep 2023
How do I make a code to assemble these two 4x4 matrices to get the 6x6 global stiffness matric as shown?
clear all;
clc;
K1=[1 1 -1 -1;
1 1 -1 -1;
-1 -1 1 1;
-1 -1 1 1];
K2=[1 -1 -1 1;
-1 1 1 -1;
-1 1 1 -1;
1 -1 -1 1];
%here are the two matrices

Fifteen12 on 21 Sep 2023
Edited: Fifteen12 on 21 Sep 2023
To add the matrices together, just arrange them by indices.
% Dummy values for k1 and k2
k1 = ones(4,4);
k2 = ones(4,4) * 2;
% Calculate stiffness matrix
K = zeros(6,6);
K(1:4, 1:4) = k1;
K(3:6, 3:6) = K(3:6,3:6) + k2
K = 6×6
1 1 1 1 0 0 1 1 1 1 0 0 1 1 3 3 2 2 1 1 3 3 2 2 0 0 2 2 2 2 0 0 2 2 2 2
You can make this more robust by using variables instead of hard coding the indices, but this minimal example shows the concept. Good luck with your finite elements!
thanks mate

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