Concatenating matrices using headings

New to Mathematica. I want to create and combine K1, K2, and K3 (shown in the first picture below) into the 8×8 matrix shown in the second picture below and keep the heading as shown if possible:

The three K matrices

The final matrix

Elements indicated by the same headings from each K matrix should be added together and placed at the same position in the 8×8 matrix. For example, here we have 3 elements at the position (u1,u1); one from each K matrix. These elements are 0, 0.5, and 1 and each of them is multiplied by the constant outside the matrix. Thus, they should be added together to form element (u1,u1), which is 1.354 in the 8×8 matrix. Similarly, we have one element indicated by (v2,v2), which is 1, in the matrix K1. So, that element should be at the position (v2,v2) in the 8×8 matrix. How do I do that in Mathematica?

I could define each K matrix as an 8×8 matrix with zeros as fillers, but sometimes I need to deal with bigger matrices and it gets tedious.