 The biggest difference is the distance they can cross in a single span.  A modern arch can safely span up to 800 or 1,000 feet.  While a suspension bridge is capable of spanning up to 7,000 feet.

 Compression  tension

 The load at the top of the key stone makes each stone on the arch of the bridge press on the one next to it. This happens until the push is applied to the end supports or abutments, which are enbedded in the ground.  The ground around the abutments is squeezed and pushes back on the abutments.  For every action there is an equal and opposite reaction. The ground which pushes back on the abutments creates a resistance which is passed from stone to stone, until it is eventually pushing on the key stone which is supporting the load.

 Arches are fascinating in that they are a truly natural form of bridge. It is the shape of the structure that gives it its strength. An arch bridge doesn't need additional supports or cables. Ancient Romans built arch bridges are still standing today.  These bridges are real testaments to the natural effectiveness of an arch as a bridge structure.

 A suspension bridge suspends the roadway from huge main cables, which extend from one end of the bridge to the other. These cables rest on top of high towers and have to be securely anchored into the bank at either end of the bridge.  The towers enable the main cables to be draped over long distances. Most of the weight or load of the bridge is transferred by the cables to the anchorage systems.  These are imbedded in either solid rock or huge concrete blocks. Inside the anchorages, the cables are spread over a large area to evenly distribute the load and to prevent the cables from breaking free.

 Pro: Long distance  Torsion (rotational or twisting force) All suspension bridges have deck-stiffening trusses which, as in the case of beam bridges, effectively eliminate the effects of torsion; but in suspension bridges of extreme length, the deck truss alone is not enough. Wind-tunnel tests are generally conducted on models to determine the bridge's resistance to torsional movements.

 Cable stayed suspension bridge  Bridges whose deck is supported at several points by stays and rests on one or more towers

 Clifton suspension bridge at Bristol, UK

 It is a vibration in something caused by an external force that is in harmony with the natural vibration of the original thing  It can be fatal to a bridge.  Resonant vibrations will travel through a bridge in the form of waves.  In order to mitigate the resonance effect in a bridge, it is important to build dampeners into the bridge design in order to interrupt the resonant waves.  If a bridge has, for example, a solid roadway, then a resonant wave can easily travel the length of the bridge. If a bridge roadway is made up of different sections that have overlapping plates, then the movement of one section is transferred to another via the plates, which, since they are overlapping, create a certain amount of friction.  The trick is to create enough friction to change the frequency of the resonant wave. Changing the frequency prevents the wave from building.

 the bridge structure  points of the instant bridge  Drawing of the instant bridge