How to model a manway in a side of a large diameter pipe?
Bentley AutoPIPE like most other stress programs uses 1-D finite elements which use simple Beam element center-line based theory, also known as the stiffness or displacement method, to mathematically model the piping system in three dimensional space. The system is formulated into a set of linear equations, describing the system characteristics at each degree of freedom (DOF). However, AutoPIPE differs from other applications because each point (e.g., piping, soil, beam, etc.) in an AutoPIPE modeled system has six (6) degrees of freedom. The exact formulation of these equations and their solution depends on the type of loading being investigated.
With that said, AutoPIPE can provide an approximation to model a large irregular shaped opening in a pipe run. Suggested approach:
1. Model opening as a single node point.
2. Insert point load to consider weight of cover / lid.
3. Calculate SIF (use App D or other to calculate an SIF to approximate the hole).
4. Insert SIF at node point.
Again this is an approximation. For more accuracy, suggest to performing analysis using a full FEA application.