PIPS Spec Pipe Friction Global Reduction

[swearingen]

In PIP STC01015, Structural Design Criteria, Section 4.1.7.7, there is a table that shows reductions due to pipe friction as the number of pipes increases. The reason for this is clearly explained in the section, and is only applied to the beam that the pipes sit directly on.

Just below that, in Section 4.1.7.8, there is a further 50% reduction for global design (i.e., members outside of the direct supporting beam). A few of us here have been discussing why this may be the case, but we have yet to come up with any ideas. Is there anyone here that may know?

Thanks in advance...


-5^2 = -25 ;-)

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[AskTooMuch]

From anchor point of pipes, friction starts in opposite directions. For global analysis they should cancel each other.

 

[swearingen]

AskTooMuch, yes, that makes sense and is taken care of in 4.1.7.7. It's the additional knock-down factor that I'm curious about.


-5^2 = -25 ;-)

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[AskTooMuch]

I need to read the latest PIP when I get the chance but my guess you did not understand what I meant.

In 4.1.7.7, I think it meant different pipes have could have friction running on opposite directions so it's reduced.

In Section 4.1.7.8 where it's reduced further during global analysis, it is because, say you have 1 pipe (East West direction) that has anchor point, from left of anchor point, friction goes to east direction, from right of anchor point, friction goes to west direction. So they cancel each other globally.
If you will look at older design guides of some EPC they only consider 5% or 10% even 0% of friction loads going to brace bay and foundation because they assumed to cancel globally.