Wanderlust World Wanderlust World A truss bridge uses a triangulated framework of straight members (usually steel or timber) to carry loads. The triangle is the only rigid polygon—trusses turn bending forces into pure tension and compression, allowing long spans with less material.
| Type | Pattern | Best For | Famous Examples |
|---|---|---|---|
| Pratt | Diagonals slope down toward center (↘); verticals in compression, diagonals in tension | Medium-long spans (50–150 m); railways, highways | Governor's Bridge (MD), countless railroad bridges |
| Howe | Diagonals slope up toward center (↗); verticals in tension, diagonals in compression | Timber trusses; shorter spans | Historic covered bridges |
| Warren | Equilateral triangles (no verticals); alternating compression/tension | Long spans (100–250 m); material-efficient | Sydney Harbour Bridge (arch-truss), I-35W Bridge (MN) |
| Warren with Verticals | Warren + verticals at panel points | Reduces buckling in long compression members | Many modern highway bridges |
| K-Truss | Two diagonals per panel forming "K"; shorter unbraced lengths | Heavy loads, very long spans (200+ m) | Ikitsuki Bridge (Japan), some railroad bridges |
| Baltimore / Pennsylvania (Petit) | Pratt/Warren with subdivided panels (sub-struts/ties) | Very long spans, heavy railroad loads | Hell Gate Bridge (NY), many major RR bridges |
| Vierendeel | Rectangular frames (rigid joints, no diagonals); moment-resisting | Where diagonals obstruct clearance (architectural) | Gladesville Bridge (Sydney), some building frames |
| Bowstring / Tied-Arch | Arch + tie girder; thrust contained | Long spans, aesthetic | Fort Pitt Bridge (Pittsburgh) |
Steel trusses now often hybridized: truss arches, cable-stayed trusses, truss-stiffened suspension bridges. Composites (FRP) emerging for pedestrian spans. The triangle remains the structural DNA.