1. The problem statement, all variables and given/known data Can somebody please explain me: What does it mean that Longitudinal Stiffness (EA) is equal to infinity? What does it change if for some members of a structure "EA = infinity", and for other members "EA = finite number". 2. Relevant equations I know that we use longitudinal stiffnes to calculate displacement, by Maxwell - Mohr Formula: fi = sum of integrals [N*Ń/EA dS], but what meaning has the infinity or precise value of Longitudinal Stiffness?