Running Analyses & Load Cases

The load cases

Case	Loads applied	Code check
DRY	Steel weight only (empty pipe)	Deflection review
SUS — Sustained	Weight + fluid + pressure + point loads	SL ≤ Sh (B31.3 Eq. 15)
EXP — Expansion	Thermal displacement stress range	SE ≤ SA (Eq. 17), SA = f(1.25·Sc + 0.25·Sh) or the liberal form
OPE — Operating	Everything combined (weight + fluid + pressure + thermal)	Operating position, support loads, SL & SE reported
OCC-WIND	Operating + wind (ASCE 7 or AS 1170.2)	SL + S_occ ≤ 1.33·Sh
OCC-SEIS	Operating + static-equivalent seismic	as above

For models with friction or one-way supports, the EXP range is computed the code-consistent way — as the difference between the operating and sustained solutions (the classical L1 − L2), including hot and cold excursions when T_min is set below install.

Run Analysis vs. Run All Cases

• Run Analysis solves the single case selected in the Load Case dropdown.
• Run All Cases (n) ▶▶ solves the whole relevant list in one click: SUS, EXP and OPE always, plus OCC-WIND when a wind speed is set and OCC-SEIS when seismic input is configured. When it finishes:
  • the view opens on the governing case (highest stress ratio anywhere), announced in the toast;
  • the Load Case dropdown now switches between the stored results instantly — no re-solving;
  • the All Cases ↔ tab in the results table shows the per-element ratio matrix with the governing case highlighted;
  • the PDF report gains the All-Load-Cases Envelope page.

What happens during a solve

1. Geometry expansion — bends become arcs, tees get weld-point nodes, flanges become rigid stubs, buried pipe is subdivided. Errors here abort with an exact message (same as Check Model).
2. Nonlinear solution — one-way supports, gaps and friction are iterated with an elastic stick-slip friction model until every restraint's state is stable (details in the Technical Reference). The solve is deterministic — the same model always gives the same answer.
3. Code stress evaluation — per element, against its own specification.

Warnings and errors you may see

• "Tee at node N was SKIPPED…" — the node doesn't have exactly 3 connected elements; it was treated as a plain intersection with no tee SIF. Fix the connectivity if a real tee.
• "Nonlinear solver did not fully converge…" — results are the best-settled state; review friction coefficients and gaps at the named supports.
• "Support at node N kept alternating…" — an on/off support at its physical limit was frozen engaged; check its gap.
• "Model appears unstable or under-constrained" — a rigid-body motion is unrestrained (missing anchor/guides) — the solver refuses rather than print garbage.
• "Analysis server is waking up…" — free-tier hosting cold start; it proceeds automatically within a minute.

Modal analysis

Settings → Modal Analysis → Run Modal Analysis extracts natural frequencies and mass-participation factors (consistent-mass eigenvalue solution). The viewer's Modal Analysis pill animates each mode shape with adjustable exaggeration; the table lists frequencies and participation per direction. Aim for cumulative participation ≥ 90 % in each direction when using results for response-spectrum work.

Wind & seismic input (Settings, Pro)

• Wind — ASCE 7 (speed, exposure B/C/D, angle) or AS 1170.2 (V_R, terrain category, M_d, M_t). Load varies with elevation and projected pipe diameter (coating included).
• Seismic — GENERIC (a horizontal g-factor + direction) or AS 1170.4 (kp, Z, site class, ac, rc). Valve actuator masses generate eccentric torsion; snubbers lock.

Occasional cases superpose the increment on the converged operating state with the operating contact/friction state frozen — the standard treatment.