What Do You Know About The Origin Of A Bridge?

In the early civilization of mankind, wherever man lived and there were streams or rivers in his way, he must have searched for ways to be able to cross over. Probably nature herself provided man with his first bridge when a tree fell across a stream. Man could easily copy that and sooner he started to make tree-trunk bridges before some prehistoric engineer thought of piling up stones in the middle of a stream and laying logs from the pile to the shores. This made a simple beam or girder with one crude pier. It was but a step to build up several of these piers in a board and connecting them with logs or slabs of stone. When two logs were laid side by side and crosspieces were laid over them as a flooring, the result was a wooden girder bridge.  These types are still built across small streams in country districts. Stronger girder bridges are now built with iron or steel beams and the strongest have steel trusses.

Any bridge has two main parts- the superstructure or the span part of the bridge and the substructure or the piers and foundations it rests upon. Foundation smight be solid for if they settle or are washed away by water current, the entire bridge may collapse. Now a days engineers more often than not go down to bedrock for the foundation and this often means a massive amount of digging. As an example for the Transbay bridge between San Francisco and Oakland the engineers went down to 70 meters below water.