General Information

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

Truss Bridge.
Steel truss bridge over a river
Main span ≅ 45 m
Type Through-truss bridge
Truss material Steel
Truss height ≅ 3 m
Deck width ≅ 3 m

Connections Failures

Figure 2 shows a schematic lateral view of the bridge.

Lateral view.
Schematic lateral view of a steel truss bridge

The vertical alignment consists of one horizontal and two inclined sectors. The continuous through-truss is supported by two abutments, two pile bents, and two cantilever piers. Figure 3 shows the connection between the truss and bent cap 1.

Truss to bent cap 1 connection.
Filed connection between bottom chord and bent cap

The bottom chord is partially embedded in the bent cap, and a crack under the bottom chord region is noticeable. Figure 4 shows the connection between the truss and bent cap 2.

Truss to bent cap 2 connection.
Filed connection between bottom chord and bent cap

Bent cap 2 is shorter than bent cap 1 (h1 > h2), and the bottom chord is connected to a steel bearing, which is detached from the bent cap. Figure 5 shows the connections between the truss and the pier caps.

Truss to pier caps 1 and 2 connections.
Connection between bottom chord and pier caps

The bottom chords are partially embedded in the pier caps, and no cracks are observable.

  • What are some possible causes for the crack and the detached steel bearing?
  • Truss Members

    Figure 6 shows a side view of a truss sector.

    Truss.
    Truss members of a steel truss bridge

    The arrangement of the web members consists of zig-zag diagonals and verticals. The upper and bottom chords are made of H-sections, the verticals are made of circular hollow sections, and the diagonals are made of built-up sections, as shown in figure 7.

    Diagonal.
    Truss diagonal made of a built-up section

    The build-up section consists of two side-by-side placed U-sections that are joined by intermittent welding.

  • What are some possible structural and/or constructive reasons for the used truss members sections?