All,

Can anyone provide a comment on how the soil spring stiffness values are calculated for bends and nodes near bends when the Peng model is used for buried pipe analysis?

I have found varied success in validating Caesar's calculation by hand using the equations in the user's guide. It seems that nodes immediately up and down stream from elbows do not follow the consistent Fy = Ftr * 0.5 * (LupstreamofNode + LdownstreamofNode). And as a note I have been using the length of the bend, not the dx dy dz offset values.

Thank you for your time,
Daniel

Remember that, in the input processor, CAESAR II displays all node labels and restraints at the From Node or To Node. Bend nodes are identified at the tangent intersection point (TIP) of the two straight runs forming the bend but this TIP is not on the pipe. Remember, too, that this To Node number (the TIP) will end up as the end of the bend in the analysis and output.
If you recalculate the length into and out of each node with this shift in mind I believe you will match the CAESAR II terms.
I found this to be a rather difficult task. It was made easier when I added additional nodes to my model - these nodes are placed at the beginning and end of each bend. Instead of referencing the TIP in determining the lengths into and out of the bend nodes, use these explicit nodes at each end of the bends.

Thank you Dave.

I found out my problem lied in misunderstanding how the nodes were redistributed after running the buried pipe builder. So my issue was calculating the anchor values not at bend nodes, but for the first node on the tangent piping downstream of the bends. It seems that Caesar breaks the bend in two (which I knew), but it also breaks the downstream portion of the bend into two separate pipes yet pushes the node of that break upstream to the center of the bend. Well, the formula I used that works is: Fy = Ftr * 0.5 [(LupstreamOfNode - 0.5*bendlength)+LdownstreamOfNode)]

Hopefully the formula is more clear than my words...

Thank you again for your time,
Daniel