Question No :1 ( Load Cases)

Presently we are doing modification job on the offshore platform.Adding water line on the existing bridge.The bridge having structural displacement of +/- 225.

The line and bridge goes from along the z- direction as per Caesar Axis.

We are using the following loads cases for the bridge piping.
W= Weight Content.
P1= Max Design pressure.
T1= Max Design Temperature.
D1, D2= Structural Displacements.
D1 D2
Dx 0 0
Dy 0 0
Dz -225 225
Rx 0 0
Ry 0 0
Rz 0 0

Case No LOAD CASE TYPE COMBINATION METHODE

L1 W+P1 SUS
L2 W+P1+T1 OPE
L3 W+P1+T1+D1 OPE
L4 W+P1+T1+D2 OPE
L5 L2-L1 EXP ALG
L6 L3-L2 EXP ALG
L7 L4-L2 EXP ALG
L8 L3-L1 EXP ALG
L9 L4-L1 EXP ALG

The above loads cases are required enough.
Or Required to add occasional load cases also listed below.
L10 L3-L1 OCC ALG
L11 L4-L1 OCC ALG
L12 L10+L1 OCC SCALAR
L13 L11+L1 OCC SCALAR

Question No 2 (Displacement direction)

Refer to attached fig some supports are taken from fixed end side and some supports taken from sliding end and also some supports on the bridge. We are considered that all supports move in one direction.
D1 D2
Dx 0 0
Dy 0 0
Dz -225 225
Rx 0 0
Ry 0 0
Rz 0 0

Its required to consider case like bridge moving apart means, some supports move on one direction and other supports move in opposite direction.
D1 D2
Dx 0 0
Dy 0 0
Dz -225 225
Rx 0 0
Ry 0 0
Rz 0 0

D1 D2
Dx 0 0
Dy 0 0
Dz 225 -225
Rx 0 0
Ry 0 0
Rz 0 0
Regards,

akula

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.

As quoted by DJ Paul axial displacements should not create problem.

The load cases you have mentioned (L10, L11, L12, L13) has been considered as expansion stresses. You shall not consider it also as a occational case. Furthur as you have mentioned the displacemention form +225 to -225 the worst expansion stress range also needed to be considerd which is T1+D1+D2 (Consider as a non linear case).