The+Beam+Bridge

**__ ​ The Beam Bridge __** First of all you need to know about the types of bridges. Let me explain :) and yes you have to read on... The **Beam Bridge**, it is also known and truss bridge, or somtimes the girder. It is the most simplist type of bridge but yet the mst expensive. The beam bridge is the most basic form made by a horizental beam that is supported by each end of the piers. The weight of the beam force goes straight down on the peirs, adding extra pressure this is why the beam itself must be extremely strong so that it wont bend under its own wieght and the weight of the traffic on top.When a load pushes down on the beam, the beam's top edge is pushed together (compression) while the bottom edge is stretched (tension). Oh I almost forgot to explain what compression and tension is... woops :) //Compression// is to press together and //tension// is the act of streching or straining. The farther apart its supports, the weaker a beam bridge gets. As a result, beam bridges rarely span more than 250 feet. This doesn't mean beam bridges aren't used to cross great distances it only means that there may be a series of beam bridges joined together, creating what's known as a "continuous span."

** This is a really good example of compression and tension against the bridge =) **

Pre-stressed concrete is an ideal material for beam bridge construction; the concrete withstands the forces of compression well and the steel rods imbedded within resist the forces of tension. Pre-stressed concrete also tends to be one of the least expensive materials in construction.But yet even the best material can stand the beam bridges biggest issue, its lenth.

Beams **

Beams used in buildings may vary in cross sectional shape. Some may be solid or hollow. The first beam is a box section, the second an I section beam and the third an L section beam. Solid beams are heavier than hollow beams. Beams like the one's below are given a special cross section for strength and rigidity. They may be as strong as the solid beams but are a lot lighter.They could be described as having good strenth to the ratio of weight.

** Images of Beam Bridges: **  **The Longest Bridge in the world:** the world's longest bridge is a continuous span beam bridge. Almost 24 miles long, the Lake Ponchartrain Causeway consists of two, two-lane sections that run parallel to one another. The Southbound Lane, completed in 1956, is made up of 2243 separate spans, while the Northbound Lane, completed in 1969, is pieced together from 1500 longer spans. Seven cross-over lanes connect the two main sections and function as pull-over bays in emergencies. Although impressive, the Lake Ponchartrain Causeway bridge underscores the drawback of continuous spans: they are not well suited for locations that require unobstructed clearance below.

**Thats sooo long .... AWESOME :):)**