Robot Structural Analysis • Smart-Book
Diagrams Window (NTM) — Detailed Explanation
This dialog controls how Robot shows internal forces, moments, reactions, and deformation diagrams on your model. (Visual only — it does not change calculations.)
1) What this window is for
The Diagrams window lets you choose which result diagrams to display and how they are scaled. You use it to quickly check force flow, bending moment shape, shear, and sometimes soil reactions for foundations.
Important: Changing settings here changes only the display (diagram size & view),
not the analysis/design results.
2) Left menu (result categories)
| Menu | Meaning |
|---|---|
| NTM | Normal force, Torsion, Moment diagrams (most used for beams/frames) |
| Deformation | Displacements (deflection/translation/rotation) |
| Stresses | Stress results (depends on element type) |
| Reactions | Support reactions at restraints |
| Reinforcement | RC reinforcement results (after RC design module) |
| Parameters | Extra diagram settings |
3) Diagram scale for 1 cm (key setting)
The boxes under “Diagram scale for 1 (cm)” define the numeric value represented by 1 cm of diagram length on screen.
Example: Mx Moment = 0.10 (kN·m) Example
- If Mx = 0.10, then 1 cm on screen equals 0.10 kN·m.
- If your real moment is 10 kN·m, diagram length ≈ 10 / 0.10 = 100 cm (very large).
- So, smaller scale numbers make diagrams look bigger; larger numbers make them smaller.
4) Force diagrams (Fx, Fy, Fz)
Fx Force (kN)
Axial force along the member local axis (often used for columns/truss members).
Fy Force (kN)
Shear force in local Y. Very common for beam shear checks (stirrups).
Fz Force (kN)
Shear force in local Z. Used when member orientation makes Z the shear direction.
5) Moment diagrams (Mx, My, Mz)
Mx Moment (kN·m)
Torsion (twisting). Often less critical, but important for edge beams, irregular frames, or eccentric loads.
My Moment (kN·m)
Bending about local Y. Frequently the main bending moment for RC beams (depends on local axes).
Mz Moment (kN·m)
Bending about local Z. Also common—especially when beams are rotated or framing direction changes.
Tip: For RC beam design, the “main” bending moment is whichever axis matches your beam’s strong bending direction.
Always confirm member local axes in Robot.
6) Elastic ground reactions (Ky, Kz)
These appear when you model soil support using an elastic ground (Winkler) model under slabs/footings.
Ky Reaction (kN/m)
Soil reaction component in Y direction (depends on your model axis orientation).
Kz Reaction (kN/m)
Soil reaction component in Z direction (commonly vertical soil pressure for foundation checks).
7) Buttons & options
All / None / Normalize / Diagram size (+ / −) Controls
- All → show all diagram types (forces/moments/reactions selected).
- None → hide all diagrams.
- Normalize → auto-scales diagrams so they fit nicely on screen (fast checking).
- Diagram size + / − → changes diagram visual size/thickness only.
Open a new window / Constant scale Important
- Open a new window → shows diagrams in a separate window (good for screenshots & dual screens).
- Constant scale → keeps the same scale for all members, so you can compare beams correctly.
Engineering rule: Use Constant scale when comparing moments/shears between members.
Use Normalize only for quick viewing, not for comparison.
8) Practical settings (how engineers use it)
| Goal | Turn ON | Recommended |
|---|---|---|
| Beam bending check | My or Mz (main moment) | Constant scale ON, Normalize OFF |
| Beam shear check | Fy or Fz (main shear) | Constant scale ON |
| Load path / axial | Fx | Confirm local axes |
| Foundation soil pressure | Ky / Kz reactions | Check deformation too |
9) Common mistakes (avoid these)
- Using Normalize for design comparison (it can mislead you visually).
- Comparing beams without Constant scale ON.
- Not checking member local axis direction → wrong interpretation of My vs Mz.
- Choosing a bad “1 cm scale” value → diagrams become too small or too huge.