# Documents: Bridge and Cantilever Bridge Essay

Submitted By tonyaantipova
Words: 1232
Pages: 5

Cantilever Bridge
Describe the bridge and how it distributes the forces acting on it. Including an explanation of what makes this type different then beam bridge.
A cantilever bridge could be said to be a variation on the basic beam bridge. The roadway of the bridge is held in place by cantilevers, which are long structures, or arms, projecting out into the water, but which are anchored on only one end. A diving board is a good example of a cantilever: although anchored on only one end, it can support a lot of weight.
In a cantilever bridge, there are the outer beams, the cantilevers, and the central beam. The outer beams are attached firmly to shore, while the cantilevers are then attached to these outer beams. The cantilevers projecting out from the outer beams, or supporting piers on the opposite shores, are then joined by a central beam.
The Forth Railway Bridge in Scotland and the Quebec Bridge in Canada are both famous examples of cantilever bridges.
Labeled illustration identifying the distribution of forces.

Advantages of cantilevers -Building out from each end enables construction to be done with little disruption to navigation below. The span can be greater than that of a simple beam, because a beam can be added to the cantilever arms. Cantilever bridges are very common over roads. Because the beam is resting simply on the arms, thermal expansion and ground movement are fairly simple to sustain. Cantilever arms are very rigid, because of their depth.
Disadvantages of cantilevers - Like beams, they maintain their shape by the opposition of large tensile and compressive forces, as well as shear, and are therefore relatively massive. Truss construction is used in the larger examples to reduce the weight.
When would you use this type of bridge?
You would use this type of bridge where is open water
What are some example of this type of bridge?
Suspended Span Cantilever Bridge, Balanced Cantilever Bridge
Arch Bridges
Describe the bridge and how it distributes the forces acting on it. Including an explanation of what makes this type different then beam bridge.
Arch bridges are one of the oldest types of bridges and have been aroundd for thousands of years. Arch bridges have great natural strength.
They were originally built of stone or brick but these days are built of reinforced concrete or steel. The introduction of these new materials allow arch bridges to be longer with lower spans.
Instead of pushing straight down, the load of an arch bridge is carried outward along the curve of the arch to the supports at each end. The weight is transferred to the supports at either end.
These supports, called the abutments, carry the load and keep the ends of the bridge from spreading out.
Labeled illustration identifying the distribution of forces.