Best Practices: Pretensioning Setup for Rectangular Membrane/shell Structures

[FEAnalyst]

@Broamb

My revised understanding:

1. Step 1: Gravity + Wind Load (establish baseline loading state)
2. Step 2: Add pretensioning with Nlgeom ON (should reduce displacement from Step 1)

Isn’t pretensioning supposed to happen before operational conditions such as wind load ? The loading sequence should correspond to real life situation.

@Broamb

Is Nlgeom absolutely critical for thin membrane pretensioning effectiveness?

Nlgeom has to be enabled to get accurate results when there are large strains/displacements, preloads or structural instabilities (buckling). This is nicely explained here: Flow Chart: Do I need nonlinear geometry? - Enterfea and here: Geometrically nonlinear analysis - how does it work? - Enterfea

@Broamb

Should pretensioning forces be applied as incremental in Step 2, or as total values?

This is explained in point 2 here: Understanding multistep analyses

@Broamb

Current issue: With elastic material and thin geometry, I suspect the membrane isn’t developing sufficient membrane action to benefit from pretensioning - it’s behaving more like a flexible plate in bending.

Keep in mind that PrePoMax and CalculiX have both shell elements and membrane elements. The latter have no bending stiffness.