Question 1.
Ans
Regarding the displacement of the bridge,you r telling in +/- Z direction movement i.e. +/- 225.
1. checkout lateral direction displacements.As your Z direction is in axial direction of pipe/bridge.
2. Axial directiion movement will not affect much as loop will be provided for its makeup.
3. By putting Rx/Ry/Rz = 0 the supporting will not allow rotation,check this.......is rotation restriction
is specified by the client at the supporting?
4. Yes occoational cases need to be added, but that must be
a) (ope+wind/seismic) for load checks and
b) pure wind/seismic for load checks if required otherwise not to be checked.
c) pure wind/seismic + sus for stress checks.

we have seen in occational cases the system sometimes fails in stresses
or loads at guides are more,So better to include them

Question 2.
Ans
Regarding the displacement with and apart.
I must say if one portion is fixed and other is sliding
in cases:
a) fixed portion will be having
D1 D2
Dx 0 0
Dy 0 0
Dz -225 225
rx)
ry) to be free
rz)
And extrapolate the displacement from fixed end to sliding end corresponding to the supporting distances.

put these extrapolated displacements at corresponding supports and analyse the system.

And what I find in our project there is difference in displacements of brizge and plateform becouse of
this extrapolatation.
So if you r doing the analysis of platform and bridge simultanously u have to put extrapolated displacements
at the bridge supports and primary displacements (Dz +/- 225) at the platform supports.