Final answer:
Tension in an arch bridge can be caused by temperature changes, movement, and varying loads, as well as external forces such as wind. Architectural design including voussoirs and keystones also plays a crucial role in maintaining a bridge's integrity against these tension forces.
Step-by-step explanation:
What Can Cause Tension in an Arch Bridge?
One of the fundamental aspects of an arch bridge is its ability to span large areas by resolving forces into compressive stresses, thereby eliminating tensile stresses. These compressive stresses push downward, creating an outward thrust at the base known as thrust. For the bridge to maintain stability and prevent collapse, this thrust must be counteracted by tension through either internal ties or external bracing such as abutments.
Factors causing tension in an arch bridge include:
- Temperature changes: As the bridge materials expand and contract due to temperature variations, it can lead to stress and tension within the structure.
- Motion of objects on the bridge: The dynamic loads from vehicles or pedestrians can cause vibrations and movement that lead to tension.
- Changes in total load: An increase or decrease in the load the bridge carries, such as heavier traffic or accumulated snow, can affect the tension.
In addition to these factors, historical examples like the Tacoma Narrows Bridge collapse in 1940 demonstrate how external forces like wind can induce tension. The bridge started oscillating at its resonant frequency, and when damping decreased, the result was the rupture of support cables and the eventual failure of the structure. A similar outcome can occur due to corrosion, as visualized in Figure 14.1.1, where rusted beams like those on the Nandu River Iron Bridge, compromise the integrity of bridges.
Lastly, the architectural design of arches, using wedge-shaped stones called voussoirs and a central keystone, emphasizes the importance of side support to maintain strength and stability against tension forces.