How to define the stiffness (K) of celas2 element

Hello everybody,

i guess it is easy to solve but i can't define the stiffness of a celas2-element. I created 1D --> springs --> celas2, Chose 2 nodes, Chose dof (3), Chose property, but still i don't know how to apply the stiffness (K).

It tried with PARAM --> ELASSTIF, but it doesn't work.

Thank you in advance

Greets,

Fatih Uysal