Member Displacements

These in turn can be extracted by the same location vectors into the member end displacements in global axes. For any member, the i-th term of member end displacements is equal to:

$$u[i] = u_{s}[loc[i]]$$ (3.14)

These elements are augmented to the member displacement vector in global axes $\mathbf{u_s}$. In order to calculate member forces, we need to change those displacements into the local member axes. We do this using the contragredience equations, 3.7:

$$e = \mathbf{B^T} \cdot \mathbf{u}$$ (3.15)