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

Bent Caps 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. The truss-to-bent caps and truss-to-pier caps connections are shown in figures 3 to 5.

Bottom chord 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.

Bottom chord 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.

Bottom chord 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 with verticals. Upper and bottom chords are made of H-profiles, the verticals are made of circular hollow profiles, and the diagonals are made of a built-up section that consists of two side-by-side placed U-profiles that are joined by intermitted welding, as shown in figure 7.

    Diagonal.
    Truss diagonal made of a built-up section
  • What are some possible structural and/or constructive reasons for the used truss members sections?