How does Autopipe calculate the Pressure Extension & Pressure Thrust forces?
Autopipe calculates the pressure thrust based on cap pressure force – poissons effect i.e using inside diameter for the poissons term. This term is at the analysis level acting on the inside diameter and not a code compliance hoop stress term which uses outside diameter. • Pressure thrust reaction at anchor. Rpressure = p.Ai – v.p.Di/2t x As where Ai is the internal pipe area and As is the X-area of the pipe, t is the wall thickness. • Pressure extension Ext = (p.Ai/As/Elong – v.p.Ri/t/Ehoop)*tangent length Note: Autopipe does not report the cap internal pressure load at an anchor unless it is unbalance thrust across a flexible joint with the pressure analysis option checked when performing a static analysis. Note: The program calculates displacements then back-calculates forces and moments from the stiffness matrix equations which many times can be difficult to manually re-produce.
