What are those bridges?

1) Beam Bridge
A beam bridge is a rigid, horizontal structure that rests on two end supports, and carries traffic loads by acting structurally as a beam. It is a direct descendant of the log bridge, now more normally made from shallow steel.

2) Arch Bridge
An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side.

3) Cantilever Bridge
A cantilever bridge is a bridge built using cantilevers: structures that project horizontally into space, supported on only one end. For small footbridges, the cantilevers may be simple beams; however, large cantilever bridges designed to handle road or rail traffic use trusses built from structural steel, or box girders built from prestressed concrete.

4) Suspensron Bridge (串錯字牙,應該系"suspension bridge"懸橋/吊橋)
A suspension bridge is a type of bridge that has been created since ancient times as early as 100 AD. Simple suspension bridges, for use by pedestrians and livestock, are still constructed, based upon the ancient Inca rope bridge.

如果吾明既話,可以上:
http://en.wikipedia.org/wiki/Beam_bridge
http://en.wikipedia.org/wiki/Arch_bridge
http://en.wikipedia.org/wiki/Cantilever_Bridge
http://en.wikipedia.org/wiki/Suspension_bridge