General Information

Figure 1 shows a truss bridge that is used by motorcycles, bicycles and pedestrians.

Truss bridge.
Steel truss bridge over a creek.
Main span ≅ 10 m
Type Underslung truss bridge
Truss material Steel
Truss height ≅ 0.3 m
Deck width ≅ 1.2 m

Truss Geometry

Figure 2 shows a side view of the main span.

Truss bridge.
Side view of a steel truss bridge.

The truss is made of rectangular hollow sections, the height h ≅ 0.3 m, and the distance between the verticals b ≅ 1 m. The diagonals are connected to the verticals, and the inclination α ≅ 9°.

  • How efficient is the truss geometry?
    Would there be a structural safety or serviceability problem without the diagonals?
  • Cross-Frame

    Figure 3 shows a bottom view of the bridge.

    Truss bridge.
    Steel truss bridge viewed from below

    The deck is made of timber boards; they are connected to the trusses' upper chords and a stringer, which is connected to a cross-frame that consists of five members: two horizontals (1 and 2) and three verticals (3 to 5). The horizontals (1 and 2) are connected to the trusses' verticals and bottom chords. Figure 4 shows a bottom view of a cross-frame to truss connection.

    Cross-frame to truss connection.
    Structural connection of a steel truss bridge

    The horizontals (1 and 2) and the truss are connected by welding; the former does not touch the latter.

  • What are the structural problems with the above-shown weld connection?
    What is the purpose of members 2, 3, 4, and 5?
  • Alternative Variant

    Figure 5 shows a schematic three-dimensional view of the used bridge and a beam bridge variant with I-section girders.

    Truss bridge and beam bridge.
    Three-dimensional drawings of a truss bridge and a beam bridge.

    The truss is continuous, while the beam bridge model consists of three simply supported beams. The deck and the stringers are equal on both bridges, while cross-beams are installed in the beam bridge instead of cross-frames.

  • What are some possible reasons for choosing the truss bridge?