Analyze the given truss structure using the stiffness method. Clearly state the steps and (matrix) equations used in the problem-solving process.
a) Label the degrees of freedom (both free and restrained DOFs) of the structure.
b) Determine the stiffness matrix of each element in the local and global coordinates.
c) Assemble the structure stiffness matrix Kff considering free DOFs, then write the complete equilibrium equations Kff Uf = Pf and solve for the unknown displacement vector Uf.
d) Calculate the basic deformation and force of each truss element.
e) Calculate the reactions of the structure and check the global (structure level) equilibrium.