Hi,

in my latest time history analysis for a piping system subjected to surge, I noticed the "% force added" values in the 'included mass report' for some of the (force-time) spectrums have been presented with negative figures (e.g. -25%). these spectrums are acting on the pipe segments where there is an axial restriction.
I wonder to know how one should interpret that?
I am aware that the axial force spectrum acting on an axially restricted pipe segment may lead to DLF close to one (high system frequency- rigid criteria), I expected to receive highly active forces with a large amount of missing mass but, I did not expect to see negative values!

many thanks in advance,

up

tumbleweed....

What's the force directionality / pipe reaction relative to the axial restraint?

the surge force is acting along the axis of pipe and in that particular segment there is an axial restriction so, the reaction is also in axial direction.

I am shooting from the hip, but it's possible to have a DLF < 1 if the dynamic response is less than the static response.

An axial load on a pipe with an axial restraint could be one of those situations where beam analysis comes to this conclusion, especially if the force component acts on a small time scale - analogous to the Costa Rican Basilisk that can run across water, but not stand on it.