General Information

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

Truss bridge.
Wooden truss bridge over a river.
Main span ≅ 10 m
Type Underslung truss bridge
Truss material Timber
Truss height ≅ 1 m
Deck width ≅ 1.5 m

Efficient Span Range

Figure 2 shows a schematic lateral view of the bridge.

Lateral view.
Schematic drawing of a wooden truss bridge.

A shore span s ≅ 5 m, and a main span m ≅ 10 m. A side view and a schematic partial three-dimensional view of a bridge sector on shore 1 are shown in figures 3 and 4, respectively.

Shore 1.
Shore span and main span of a wooden truss bridge.

A shore span consists of two longitudinal beams and transverse decking; a main span, of two knee-braced trusses, two transverse beams, two longitudinal beams—same cross-section as the shore span beams—and transverse decking.

Three-dimensional view.
Three-dimensional structural drawing of a wooden truss bridge.
  • What are other possible main span variants made of timber?
  • Knee-Braced Trusses

    Figure 5 shows a knee-braced truss sector viewed from above.

    Knee-braced truss.
    Knee braced timber truss sector with gaps.

    Upper and bottom chords consist of two side-by-side placed boards; the verticals and diagonals, of a single board. The truss members are connected by nails and nuts and bolts. Verticals and diagonals are connected to the upper and bottom chords on the external vertical side. A gap in the upper and bottom chords is noticeable. Figure 6 shows a side view of a knee-braced truss sector.

    Knee-braced truss.
     Knee braced timber truss sector.

    Diagonal 1 has two empty holes and the bottom nut and bolt is placed near the edge; diagonal 2 does not have the bottom nut and bolt. Eccentric joints (yellow dashed lines) are noticeable. Figure 7 shows a side view of a knee-braced truss in the mid-span region.

    Knee-braced truss (mid-span region).
    Mid-span region of a timber truss bridge.

    The mid-span vertical is the truss member with the largest cross-section and is also used as a road safety barrier. Figure 8 shows a side view of a knee-braced truss.

    Knee-braced truss.
    Knee braced timber truss.

    Knee braces 1 and 2 are different in size, inclination, and bottom chord connection position. Figure 9 shows a side view of two knee braces in the column region.

    Knee braces.
    Two knee braces in the column region.

    Each knee brace has an empty hole in the column region. Figure 10 shows two further knee braces viewed from the front.

    Knee braces.
    Buckling deformation of two timber knee-braces.

    Buckling deformation is noticeable, especially on the marked brace. Figure 11 shows a knee-braced truss to column connection.

    Knee-braced truss to column connection.
    Connection between knee braced timber truss and column.

    Column and truss chords are connected side-by-side by nuts and bolts. Figure 12 shows a side view of a knee-braced truss.

    Knee-braced truss.
    Irregular diagonal layout of a knee braced timber truss.

    The diagonal layout is asymmetric, and there is a field without diagonal.

  • How efficient are the knee-braced trusses?
    How simple and precisely can the structural behavior of the knee-braced trusses be predicted?
  • Bridge and River Discharge

    Figures 13 and 14 show the bridge during a low and a high river discharge, respectively.

    Low river discharge.
    Timber truss bridge over a river with a low discharge.
    High river discharge.
    Wooden truss bridge over a river with a high discharge.
  • How does a river discharge change structurally affect the bridge?
  • Bridge Over a Period of Time

    Figure 15 shows a bridge sector within a period of about 3 months.

    Bridge over time.
    Time = 0 Time ≅ 3 months
    Wooden truss bridge over a period of time.

    After about 3 months, most timber elements have a different color, and vegetation in the water level region is noticeable.

  • Does the color change affect the mechanical parameters of the timber elements?
    Dose the vegetation affect the durability of the timber elements?