Simple Beam Bridge
A simple Beam design with a single span of approximately 6 metres.
A beam or "girder" bridge is the simplest and most inexpensive kind of
In its most basic form, a beam bridge consists of a horizontal beam that
is supported at each end by piers. The weight of the beam pushes
straight down on the piers.
The beam itself must be strong so that it doesn't bend under its own
weight and the added weight of crossing traffic. When a load pushes down
on the beam, the beam's top edge is pushed together (compression) while
the bottom edge is stretched (tension).
Pre-stressed concrete is an ideal material for beam bridge construction;
the concrete withstands the forces of compression well and the steel
rods embedded within resist the forces of tension. Pre-stressed concrete
also tends to be one of the least expensive materials in construction.
But even the best materials can't compensate for the beam bridge's
biggest limitation: its length.
The further apart its supports, the weaker a beam bridge gets. As a
result, beam bridges rarely span more than 80 metres. This doesn't mean
beam bridges aren't used to cross great distances -- it only means that
they must be daisy-chained together, creating what's known in the bridge
world as a "continuous span."