← Verification — Linear (Frames & Trusses)
V2.1 — Symmetric two-bar (A-frame) truss
ExactDescription
A symmetric two-bar (A-frame) pin-jointed truss under a vertical apex load — member forces and apex deflection.
Reference
Method of joints and virtual work (closed form): F = P/(2 sinθ), δ = PLm/(2EA sin²θ).
Model
Two axial (pin-ended) truss members meeting at a shared apex node, each pinned to its own ground support, under a vertical load applied at the apex. Truss members carry axial force only, no bending.
| Apex load, P | 20 kip |
| Half span | 120 in |
| Height | 90 in |
| Member length, Lm | 150 in |
| Elastic modulus, E | 29,000 ksi |
| Member area, A | 5 in² |
Comparison
| Quantity | Reference | vfopro | % diff | Status |
|---|---|---|---|---|
| Apex vertical deflection (in) | -0.0287 | -0.0287 | -0.00% | Exact |
| Apex lateral deflection (in) | 0 | 0 | n/a | Exact |
| Left member axial force (kip, +tension) | -16.67 | -16.67 | +0.00% | Exact |
| Right member axial force (kip, +tension) | -16.67 | -16.67 | +0.00% | Exact |
| Left support vertical reaction (kip) | 10 | 10 | 0.00% | Exact |
| Right support vertical reaction (kip) | 10 | 10 | 0.00% | Exact |
| Left support horizontal reaction (kip) | 13.33 | 13.33 | -0.00% | Exact |
| Right support horizontal reaction (kip) | -13.33 | -13.33 | -0.00% | Exact |
Conclusion
Every reported quantity matched the closed-form value to at least 6 significant figures.
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Last updated September 22, 2026 · applies to vfopro 20260922.0.0 or later