Would one please advise how to model the foundation in SAP2000 for the follwing underground station:

The station has a 2m thick base slab with side walls and tensile anchors (underneath the slab between side walls) to resist floatation. The base slab sits directly on hard rock.

Questions:
1. Should I model the hard rock as springs (say per meter run) for downward loads or simply put a hinge each at the side walls?

2. Should I include the tensile anchors as pin supports for upward water pressure?

The tensile anchors are designed, by me, globally, i.e. the total anchor resistance is greater (with safety factor)than the total uplifting pressure on the whole base slab.

My understanding is that with such a global appraoch, an individual anchor is allowed to yield (i.e. reach its ultimate stress, the flat region). As individual anchors are allowed to yield, the anchors should not be modelled as pins in SAP2000. Without internal pins, the base slab has longger span and therefore thicker (2m) slab is required.

If anchors are to be modelled in SAP2000, I (think) have to model it as a tensile spring with an upper limit at its yielding capacity. This seems troblesome and non-linear to me.

Please comment. Thanks.