Bridges
Distributing the force
Look at the triangular pattern on this walkway that spans a distance of 20m. How are the forces distributed along the structure? Look at the animation below.

Forces acting on a triangulated structure result in either compression or tension.

Tensile forces stretch the members of a structure and try to make them longer.

Compression forces squeeze the members along their length and try to make them shorter.

Notice how the load acting on this structure is changed to tensile (red) and compression (yellow) forces in the diagonal and horizontal members
Some bridges have arches. Arches are stable structures that distribute the force, applied to the bridge, outwards as shown on the left.
The roadway on this bridge is connected to an arch via strong metal cables. As a downward force is applied to the road the cables experience tensile forces (red). This produces horizontal and vertical forces on the arch.

The combined mass of the roadway and the vehicle on the bridge is supported by cables anchored to concrete blocks at each end of the bridge.

At each point "A", "B", "C" and "D" draw the direction in which the force is acting and label the force as tensile (pull) or compression (push).
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