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Browncoat40 t1_iy71gt9 wrote

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.

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GalFisk t1_iy7zveu wrote

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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Rugfiend t1_iy896vi wrote

I grew up in Dundee - the Tay Bridge is about 1.5 miles long and sloped. We used to cycle across just so we could freewheel all the way back!

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SYLOH t1_iy71y9s wrote

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.

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breckenridgeback t1_iy7hz2f wrote

> It's mainly because most features are relatively level.

If you're building a bridge you are by nature probably not dealing with level terrain.

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SYLOH t1_iy7i27f wrote

The sides of what you're bridging probably are.

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breckenridgeback t1_iy7jb8x wrote

Often, but not at all always unless you intentionally build it that way.

The Golden Gate Bridge, for example, extends from a hill on the northern end of San Francisco (elevation a little over 200 feet) to rugged high hills/low mountains on the southern end of Marin County (which top out at 800-1000 feet). To make it level, it has to target a specific spot on the Marin coastline, then go through a tunnel.

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SYLOH t1_iy7kiyd wrote

Maybe a bridge constructed in the 1930s had such limitations.
But modern suspension bridges often are built tall enough for ships to pass under, with ramps that get that high on either end. They don't really care if the height change on the ramp has to be small or large on one or both ends.

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As_TheHoursPass t1_iy78ocw wrote

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.

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