General Information

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

Suspension bridge.
Wooden suspension bridge over a river.
Type Single-span suspension bridge
Main span ≅ 90 m
Deck width ≅ 2 m
Deck width to main span ratio ≅ 1:45
Pylon Reinforced concrete (H-shaped)
Girder Timber transverse beam

Hanger Rods

The hangers are made of steel rods, as shown in figure 2.

Hanger rod.
Steel hanger rod of a wooden suspension bridge
  • What are some possible reasons for using hanger rods instead of hanger cables?

    • Figure 3 shows a hanger rod top region.

    Hanger rod 1.
    Hanger rod top with a not-closed hook

    The rod top is not-closed hook shaped; the white arrow represents an axial force F. Figure 4 shows a further hanger rod top region.

    Hanger rod 2.
    Hanger rod top with a closed hook

    The rod top is closed hook shaped.

  • Does hanger rod 1 behave like hanger rod 2 when subjected to an axial force F?

    • Hanger Rod to Timber Girder Connection

    Figure 5 shows a schematic partial cross-section of the bridge.

    Cross-section.
    Cross section of a wooden suspension bridge.

    Hanger rod and timber girder are connected by an additional rod, washer, and nut. Figure 6 shows a hanger rod to two side-by-side placed timber girders connection viewed from above.

    Hanger rod to timber girders connection 1.
    Connection between hanger rods and timber girder using additional rods

    The timber girders are marked by the numbers 1 and 2. Additional rods 1 and 2 are differently shaped.

  • Does the support of girder 1 behave like the support of girder 2?

    • Figure 7 shows a further connection.

    Hanger rod to timber girders connection 2.
    Connection between hanger rods and timber girder using additional rods
  • How much load can be transferred from additional rod 1 to the hanger rod?

    • Figure 8 shows a connection viewed from below.

    Hanger rod to timber girders connection.
    Connection between hanger rods and timber girder using washers and nuts
  • What are the main problems?

    • Timber Condition

    Figure 9 shows a main span sector viewed from below.

    Main span.
    Girder connection of a wooden suspension bridge

    Vegetation growing on the two timber girders is noticeable.

  • How does the timber condition affect the mechanical parameters of the girders?

    • Hanger Rod to Timber Girder Connection Failures

    Figure 10 shows a main span sector viewed from below.

    Main span.
    Wooden suspension bridge with two failed connections between hanger rods and timber girder

    Due to the connection failures, girders A1 and B1 are not supporting the stringers.

  • What are some possible failure reasons?
    Are those failures affecting the safety of the bridge?

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