Verification › V.01 Trusses
V.01.13D Space Truss: Axial Forces
All 90 values STAAD.Pro prints matchOpen in the app and solveNo sign-up needed: it runs in your browser.
Problem
Find the support reactions and member forces of a space truss carrying a horizontal load at its apex.
Reference
- Beer, F. P. and Johnston, E. R., Vector Mechanics for Engineers: Statics, 4th ed., McGraw-Hill, p. 216, Problem 6.20.
- STAAD.Pro verification problem "Truss 04: Axial Forces on 3D Space Model"; its input file is used unedited.
Model
- Joints 1 (1, 0, 0.6), 2 (1, 0, −0.6), 3 (−0.8, 0, 0), 4 (0, 1.5, 0) m
- Truss members 1-4, 2-4, 3-4, 1-2, 2-3, 3-1; AX 0.001 m², E 2 × 10¹¹ N/m²
- Joints 1 and 2 free in Z only; joint 3 free in X only
- 2700 N in +Z at joint 4
Comparison
| Member | Hand calc. | Textbook | STAAD.Pro | Sutranet | Difference |
|---|---|---|---|---|---|
| 1 (1-4), compression | 4275 | 4275 | 4275.00 | 4275.0000 | none |
| 2 (2-4), tension | 4275 | 4275 | 4275.00 | 4275.0000 | none |
| 3 (3-4) | 0 | 0 | 0.00 | 0.0000 | none |
| 4 (1-2) | 0 | 0 | 0.00 | 0.0000 | none |
| 5 (2-3), compression | 4269.07 | 4270 | 4269.07 | 4269.0748 | none |
| 6 (3-1), tension | 4269.07 | 4270 | 4269.07 | 4269.0748 | none |
| Reaction | Hand calc. | Textbook | STAAD.Pro | Sutranet | Difference |
|---|---|---|---|---|---|
| Joint 1, FX | 1800 | 1800 | 1800.00 | 1800.0000 | none |
| Joint 1, FY | 3375 | 3375 | 3375.00 | 3375.0000 | none |
| Joint 2, FX | −1800 | 1800 | −1800.00 | −1800.0000 | none |
| Joint 2, FY | −3375 | 3375 | −3375.00 | −3375.0000 | none |
| Joint 3, FZ | −2700 | 2700 | −2700.00 | −2700.0000 | none |
- The truss is statically determinate, so joint equilibrium gives the exact answer: the legs carry 2700 × 1.9 / 1.2 = 4275 N and the base members 2250 × √3.6 = 4269.07 N. The textbook rounds the latter to 4270.
- Every reaction and member end force STAAD.Pro prints (90 values, including the zero shears and moments of the truss members) matches to the last printed digit.
Reproduce in Sutranet CAD
- Open the project in the app (no sign-up needed), or download the file and open it with 📂 Import Job JSON in the File group.
- Run Analysis (Static) on load case 1 with P-Delta Analysis unticked.
The app works in SI units; results in kip and inch are converted (1 kip = 4.448 kN, 1 kip-in = 0.1130 kN·m, 1 in = 25.4 mm).
Automated test: staad_space_truss.rs, run on every change.
Run your own models the same way
Create free accountFree account: build frames, trusses and towers, import STAAD .std files, and run IS 800 and AISC design checks in your browser.