What is a Vierendeel truss?
A Vierendeel truss is a girder consisting of a top chord, a bottom chord and vertical posts in between, without diagonals. In Dutch it is called a vierendeelligger. It looks like a ladder on its side. Because there are no diagonals, the connections between the chords and posts must be rigid (moment-resisting). The girder is named after the Belgian engineer Arthur Vierendeel, who developed the system at the end of the 19th century.
Difference from a conventional truss
In an ordinary truss the members form triangles. The members are then loaded mainly in tension and compression, and the joints can in principle be pinned. A Vierendeel truss has rectangular openings. The load is carried because the chords and posts work in bending, with rigid joints at the heart of the structure.
The consequences:
- For the same span and load, a Vierendeel truss is heavier and less material-efficient than a conventional truss.
- The joints are critical: they must be large and strong, often with tapered corners (haunches).
- The deformation (deflection) is greater than for a comparable conventional truss.
| Conventional truss | Members form triangles and are loaded mainly in tension and compression; joints can in principle be pinned. |
|---|---|
| Vierendeel truss | Rectangular openings; the chords and posts work in bending, with rigid joints at the heart of the structure. |
Why choose a Vierendeel truss?
The great advantage is the clear, rectangular openings. Doors, windows, corridors or services can pass through them. Applications:
- Storey-height girders in buildings, where the openings between the posts serve as windows or passageways.
- Canopies and footbridges, where diagonals would be in the way.
- Bridges: the Vierendeel bridge, widely used especially in Belgium.
- Facades with a regular grid that also contributes structurally.
Tips
- Do not design or alter it yourself: sawing out a post or enlarging an opening in a Vierendeel truss directly affects its load-bearing capacity. Have every alteration calculated by a structural engineer.
- Pay attention to the joints during renovation: cracks or corrosion at the corners are the first thing an inspection looks at.
Related terms
- Girder
- Truss
- Truss bridge
- Castellated beam
- Portal frame
- Buckling
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