shell connections by using springs

Hi everyone, 

For my master thesis I'm making a parametric design of a concrete tube in tube tower. 

The goal is to use precast concrete elements. But at the moment I'm struggling with making the connections between the elements. I have the feeling that all my different shell elements are rigid connected. With the help of springs I tried to give in this example the corner connections of the outer tube different values, but it doesn't matter how low or high i set the spring stiffness, the displacement doesn't change were I expected it to change a little bit when the connection between the elements gets weaker. 

Hope some one can help me with this!