I am trying to write the correct parameters for the hyperbolic gap material.
but the units are different from the opensees manual. my question is should I follow opensees units as I should put the stiffness values or follow the navigator and put the modulus of elasticity?
The units that you need to use when defining any material (not only the Hyperbolic Gap material) depend on how you will be using the uniaxial material. If you are using it to model a force vs. displacement relationship you will need to use units of [Force] and [Length]. On the other hand if you are using it to model a stress-strain relationship you will need to use units of [Force/Length^2] and [Length/Length]