I just realized last night I’ve never seen that, even though often times bridges are connecting cliff faces or different bodies of land. So… why? Why do they always seem to start on the same level?
Also please let me know if that’s the wrong tag… mental five year old me wasn’t sure.
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I’m not sure exactly what you mean; curved or sloped?
Either way, keeping a bridge straight and level is simplest. It distributes loads evenly on both sides, allows the builder to use straight and square members (rather than something that’s slightly off), and things like that. They can make bridges with significant slopes and curves; freeway interchanges are a good example. But they are more complicated. And if a bridge needs a slight slope, oftentimes it’s easier to simply fill in dirt on the low side to make it level rather than have a bridge compensate for being less balanced.
It’s mainly because most features are relatively level.
We don’t really have many problems making a ramp.
We build them to connect surface and elevated highways/roads all the time.
Bridges are built to last a very, very long time, and the simpler you make them the longer they will last.
A sloped bridge is going to have an uneven distribution of force. One end will be more affected by its own weight than the other. That’s not good for longevity.
The river bridge that I cross every time I go to or from work is perceptibly sloped. It was the most practical way to buid that particular bridge. Building them level when possible is often easier though.
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