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Posts tagged: analysis-modelling

7 posts tagged with “analysis-modelling”.

  1. Zero Mass Participation in ETABS: Why Your Modal Results Are Wrong and Where to Look

    The UX and UY columns read zero, sometimes with a period that makes no sense. The model ran, nothing crashed, and the dynamics are completely wrong. It's rarely mysterious: the table itself tells you which of four causes you've got.

    5 min read

  2. ETABS "Structure Is Unstable or Ill-Conditioned": What It Means and How to Fix It in Minutes

    The analysis stops, the log fills with capital letters, and the instinct is to click around the model hoping to spot it. That can eat an afternoon. The warning is far more informative than it looks, and there's a sequence that finds the cause in minutes.

    6 min read

  3. P-Delta Won't Run in ETABS: What's Actually Wrong and How to Fix It

    The model runs perfectly. You switch on P-Delta and everything stops. P-Delta almost never fails on its own: the model has a real problem linear analysis was tolerating, and the iteration is the first thing honest enough to refuse.

    5 min read

  4. Diaphragm Assignment in ETABS: The Mistake That Quietly Drops Your Seismic Mass

    Miss a diaphragm on a floor, or assign it to the wrong thing, and nothing complains. The model runs, the seismic loads generate, the results look complete. Part of the building's mass has quietly stopped participating, and the accidental torsion on that floor has disappeared.

    5 min read

  5. Stiffness Modifiers in ETABS: Why One Uniform Value Corrupts Your Load Path

    Pick one number, often 0.35, and apply it to everything. It feels consistent. It's actually one of the quieter ways to get a load path wrong, because the point of cracked-section modifiers is that different elements crack differently.

    5 min read

  6. "The Software Said So" Was Never an Engineering Justification

    The model gave a number, the number went in the report, and nobody asked whether it was right. That was a problem before AI. It's a bigger one now.

    5 min read

  7. The Shear Modifier Everyone Forgets: f12 on Walls in ETABS

    Most engineers diligently crack their walls for bending and leave the shear stiffness at full value. For squat walls, spandrels, and basement walls, that single oversight quietly distorts the entire lateral distribution.

    6 min read