Is there any option to constraint in only one direction (i.e I want restrict the movement of the body in - Z direction and not in + Z direction)
I tried with simply supported contraint option but it is restricting in the both the direction (- Z and +Z directions)
A traditional CGAP is really a simple bilinear node to node spring. When the gap has no separation, the "closed" stiffness is used. When there is a separation, the open stiffness is used. The closed stiffness is typically defined several orders of magnitude larger than the joint material. The open stiffness is typically very low - just large enough to prevent numerical problems.
In SOLs 106 & 129, this is an iterative process. The gap status is checked at every iteration and for gaps that switch from open to closed, the open stiffness is replaced with the closed stiffness for the next iteration. For gaps that have tensile forces, the closed stiffness is replaced with the open stiffness.
For all other solution sequences, the gap status is only evaluated at the beginning of the solution. Closed gaps retain the closed stiffness throughout the entire solution. Open gaps retain the open stiffness.
2D or 3D "linear" contact can be defined in a static subcase in a SOL 103 run. The converged contact stiffness at the end of this static subcase can be included in a modal subcase in SOL 103. The parts are essentially "glued" toghether with the contact stiffness for the normal mode calculation.