A parallel-chord truss turns global bending and shear into pure axial force in the chords and diagonals — a exact method for panel-point loading, and that's why it's the standard hand technique, but it still needs every member checked in the right failure mode.
Every check above runs automatically inside the Structyze Steel Truss module — this particular module is part of the full desktop catalogue rather than the free browser trial, since the trial only carries a curated flagship set. You can still try the free trial modules right now to see the same calculation style in action on RCC Beam, Column, Slab and a handful of others.
The Example We'll Use
- Span 16 m, depth 1.6 m, 8 panels
- Panel point load (service) 20 kN
- Chord: area 2500 mm², r = 35 mm, effective length 2 m
- Diagonal: area 2200 mm², r = 28 mm, effective length 2.5 m
- Material ASTM A992/A572 Grade 50, Fy = 345 MPa
Working Through It
The panel-point load converts to an equivalent factored UDL of 12 kN/m, giving global Mu = 384 kN·m and Vu = 96 kN at mid-span. Dividing by the truss depth gives the chord force directly: 384/1.6 = 240 kN. The diagonal force follows from the shear and its angle from horizontal (38.66° here): 96/sin(38.66°) ≈ 153.7 kN.
The bottom chord in tension checks cleanly against φAgFy (utilisation 0.309). Both the top chord and the diagonal are checked in compression via AISC 360 Chapter E3's flexural buckling formula — each at its own KL/r, since the diagonal's shorter radius of gyration and longer effective length push its slenderness to 89.3 against the chord's 57.1.
What Governs, and Why
The diagonal's compression check governs at utilisation 0.403, narrowly ahead of the top chord (0.393) and well ahead of the bottom chord's tension check (0.309). This is the normal pattern for a truss with a modest depth-to-span ratio (0.10 here) — the diagonal's steeper slenderness eats into its margin faster than the chords'.
Where Structyze Takes Over
Every check above runs automatically inside the Structyze Steel Truss module — this particular module is part of the full desktop catalogue rather than the free browser trial, since the trial only carries a curated flagship set. You can still try the free trial modules right now to see the same calculation style in action on RCC Beam, Column, Slab and a handful of others.
For Steel Truss and the rest of the full catalogue — 80+ components across RCC, Steel, Composite, Timber, Masonry and more, across 20+ design codes — buy the full Structyze desktop app or see everything it does on the Software page.
Quick FAQ
Why check only one diagonal and one chord panel?
The governing (maximum-force) chord panel and a representative diagonal are enough to establish whether the truss passes overall — panels nearer the supports carry less force and pass with more room. A non-uniformly-sized truss needs every distinct member checked.
What about the joints themselves?
Chord and diagonal member checks say nothing about the gusset plate connecting them at each panel point — that's a separate check (bolt/weld group, plate tension, block shear), covered by its own connection module.
Final Thoughts
Converting truss bending and shear into member axial force is quick by hand once you have the geometry — the real work is checking every distinct member size against its own slenderness and buckling class.