Rigid diaphragm-Master Joint-Slave Joint

Hi! I was trying to create a rigid diaphragm, i need it to create a master joint and link it with all my floor. 

It's not the first time, when i use spring element the model get crazy and the element look without link with the model like in the photo and problems occurs with modal analysis (lot of rigid body modes)
 
how can i do this? how can i obtain a central master joint linked with my model? 

In the second photo you can see the element i want use like spring with infinite stiffness, in this picture are disable and in fact the modal analysis works! but if I enable the spring element that element start to move like in the first picture. 

My main goal is: Obtain a central joint for each storey where i can apply Horizontal Resultant Force.