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# Bilinear restraints to model seabed- reasonable values?

## Bilinear restraints to model seabed- reasonable values?

(OP)
I am remodelling a subsea tie-in spool analysis performed by another company. The original design was performed in Autopipe and I am using Caesar. The original values for soil vertical stiffness were as follows, and input into Autopipe:
K1 = 0.02 N/mm/mm
K2= 0.014 N/mm/mm
Fy = 5000 N/m

In Caesar I am modelling the soil vertical stiffness using bilinear restraints which have the same inputs however units are N/cm and N. Am I correct in multiplying the values above by the length of the element? The stiffness seems to be far too low resulting in large vertical displacements. The values I end up with are (with element length just over a metre):

K1 = 20.4 N/mm
K2= 14.0 N/mm
Fy = 5300 N

### RE: Bilinear restraints to model seabed- reasonable values?

Yes you would have to multiply by the length of pipe associated with a particular restraint.  This would usually be 1/2 of the pipe length on each side of the restraint.

Richard Ay

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