Beam Bridge Basics
- Gina Hagler
- Apr 9
- 1 min read
Updated: Apr 15
If you live in an urban area, you likely travel over or beneath them every day. If you live in a rural area, you likely drive on them to cross rivers or gulleys. What am I talking about? The ubiquitous beam bridge: As rudimentary as a log across a stream. So, how do they work?
Beam Bridge
Think of a log across a river. Both ends sit atop the bank on either side and are supported by those banks.
To cross the water, you walk on the log. The log must be thick enough to hold your weight. If not, it will break as you move across it.
The weight of the log holds the “beam” in place on the banks that support it when there’s no one crossing.
The weight of the log plus the weight of the load - whatever is crossing - must be supported by the banks supporting it on either end.
If the dead load (no one on it) or the live load (with someone crossing) is too heavy for the banks supporting the log, the banks will collapse, and the bridge will go down with them.
In this simple example, it is the weight of the log itself that holds the log in place on the supporting river banks. On an overpass with the vibrations caused by traffic, it takes a bit more engineering to keep the beam and supports in integrity and working.
However, the concept is the same.
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