Dear All,

I am working on an offshore-fixed platform project. I received the following load case set for Transportation condition from my Client,

L1------WNC-------------SUS-----------STRESS,DISPLACEMENTS,LOADS
L2------D1+U1-----------OCC-----------STRESS,DISPLACEMENTS, LOADS
L3------D2+U2-----------OCC-----------STRESS,DISPLACEMENTS, LOADS
L4------D3+U3-----------OCC-----------STRESS,DISPLACEMENTS, LOADS
L5------WNC+U1+U2+U3----SUS-----------STRESS,DISPLACEMENTS, LOADS
L6------L1+L2+L3+L4-----OCC-----------STRESS
L7------L1+L2+L3-L4-----OCC-----------STRESS
L8------L1+L2-L3+L4-----OCC-----------STRESS
L9------L1+L2-L3-L4-----OCC-----------STRESS
L10-----L1-L2+L3+L4-----OCC-----------STRESS
L11-----L1-L2+L3-L4-----OCC-----------STRESS
L12-----L1-L2-L3+L4-----OCC-----------STRESS
L13-----L1-L2-L3-L4-----OCC-----------STRESS

Where,
WNC -----------Pipe weight, Insulation weight,rigid weight.
D1,D2,D3-------Deck deflection during Transportation.
U1,U2,U3-------Barge Accelerations during transportation.

My Observations on the load cases are,
1. We are not supposed to combine Displacement and Acceleration to calculate stress as it is done in L6
to L13 (Code Used is ASME B31.3, No use of Appendix P is being done).
2. It is not correct to consider only D and U (without WNC) for checking loads and displacements
(As done in L2 to L4), as it is not a real case.
3. L5 must be Occasional case.

Please give in your opinion on my observations.

Thanks in Advance,
Vikas

Due to the fact that D and U occurs simultaneously (OCC Case), I believe the combinations L6 upto L13 are correct. Displacements & G-load occurs at the same instance on the barge moving and subjective to wave loads.

Regarding L2 upto L4, this is only done to get the combined effect of displacements and g-load so that it can be used in L6 upto L13 combinations. Obviously the stress values for L6 to L13 will be greater than L2 to L4 so I believe they are intermediate OCC loadcase intended for final (L6 to L13) loadcase (combination) consideration.

L5 cannot be considered as OCC. It represents standing-still load on barge (SUS Condition) while introducing D corresponds to a moving barge which is an OCC condition.

I hope this helps.

Rgrds,
Salz

Thanks A lot for reply Mr. Salz,

for Point-1
I agree that "D" and "U" have to be taken together but My concern is that "U" is primary and "D" is secondary stress which have different allowable limits and I think that they have to be checked separately. Is it not so?

for Point-2
I agree with you. If L2 to L4 were only intermediate loadcases, I would not have had a problem, but the client has asked to check loads also for L2-L4. I think that that the loads have to be checked for Real or Operating cases. What I mean is, "WNC" has to considered along with "D" and "U" (in L2, L3 and L4)in order to check Loads. Please correct me if i am wrong.

for Point-3
Ok, I got it. I think that I have seen this in one of the posts of Anindya Bhattacharya Sir also.


Thank you once again.
hoping for a quick reply.
Vikas

I request you all for your valuable suggestions.
Can anyone of Mr. Anindya, Mr. Dave and Mr. Richard, kindly help me out.
Regards,
Vikas

Can anybody please put some light on this topic?

1. I have my doubts D+U OCC
2. D+U for loads will give you the net effect of these loads that will be forwarded to structural department.
3. Only for 1day return period acceleration (but will not be of big importance)