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Vibrations on a bridge are not normal? I'm asking because I've been in standstil traffic (in my car) on the Lisbon "golden gate" type bridge and that thing was

Vibrations on a bridge are not normal? I'm asking because I've been in standstil traffic (in my car) on the Lisbon "golden gate" type bridge and that thing was freaking bouncing up and down from traffic on other lanes.

dscottboggs 2y ago
Bridges do move some normally, yes. It may depend on the type of bridge though? Certainly suspension bridges do.
- tiagod 2y ago
  It's a suspension bridge. And a solid one :) Takes 6 lanes of traffic and whole trains on the bottom.
  - throwaway211 2y ago
    Trains cross bridges easily as they're either balanced with each half on each side, or half on and half on ground. And other time's just between these stable points. Furthermore, trains run on tracks which reduces chance of turning acceleration.
    - bobthepanda 2y ago
      Yes and no. Railways work well in the center of bridges. One bridge that violates this principle is the Manhattan Bridge; it was built before we had fancy engineering simulations or much experience with railway suspension bridges at all, and so the lower deck is a pair of railway tracks on either side of a roadway. This unusual design is very stressful on the bridge and has resulted in expensive rehabilitation programs.
    - buildbot 2y ago
      Unless it’s a floating bridge…
      - throwaway211 2y ago
        The thing about floating bridges is they don't need to span a waterway. The just need to link the part where getting onto the bridge then the bridge itself move to the exit section. Floating bridges also don't necessarily need to have fixed points to load and unload. With suitable stabilisation and propulsion, they should be able to move to any number of loading and unloading points. We could have a floating bridge per train, vehicle, or any unit or set of users.
      - bobthepanda 2y ago
        there will be a rail link across a floating bridge in seattle opening in 2025. it was supposed to open earlier, but the contractor messed up the concrete pour and is fixing it at their own cost. but that doesn't have much to do with the fundamentals of the floating bridge itself.
        deleted 2y ago
        [deleted]
tiagod 2y ago
Interestingly, the 25 of April Bridge in Lisbon was made by the American Bridge Company, same as the Bay Bridge, but not the Golden Gate. And yes, it's normal. That bridge is very well maintained (there's a whole team there working daily, afaik, and I've witnessed many interventions in the past).
- rob74 2y ago
  Now that you mention it, the diagonal braces on the piers (no idea how they're actually called) look very similar to the Bay Bridge. But to the casual observer, the number of piers and the color look more like the Golden Gate bridge, plus that's by far the better known one, so I'm not surprised it got this nickname...
  - tiagod 2y ago
    I agree, and it's a very common misconception among locals that it's related to the Golden Gate bridge
BurningFrog 2y ago
Depends on the bridge type, I guess. But it's true that big structures are often designed to move as a way to deal with forces. It's much better than something firm that doesn't move until it snaps.

dscottboggs 2y ago

Bridges do move some normally, yes. It may depend on the type of bridge though? Certainly suspension bridges do.

tiagod 2y ago
It's a suspension bridge. And a solid one :) Takes 6 lanes of traffic and whole trains on the bottom.
- throwaway211 2y ago
  Trains cross bridges easily as they're either balanced with each half on each side, or half on and half on ground. And other time's just between these stable points. Furthermore, trains run on tracks which reduces chance of turning acceleration.
  - bobthepanda 2y ago
    Yes and no. Railways work well in the center of bridges. One bridge that violates this principle is the Manhattan Bridge; it was built before we had fancy engineering simulations or much experience with railway suspension bridges at all, and so the lower deck is a pair of railway tracks on either side of a roadway. This unusual design is very stressful on the bridge and has resulted in expensive rehabilitation programs.
  - buildbot 2y ago
    Unless it’s a floating bridge…
    - throwaway211 2y ago
      The thing about floating bridges is they don't need to span a waterway. The just need to link the part where getting onto the bridge then the bridge itself move to the exit section. Floating bridges also don't necessarily need to have fixed points to load and unload. With suitable stabilisation and propulsion, they should be able to move to any number of loading and unloading points. We could have a floating bridge per train, vehicle, or any unit or set of users.
    - bobthepanda 2y ago
      there will be a rail link across a floating bridge in seattle opening in 2025. it was supposed to open earlier, but the contractor messed up the concrete pour and is fixing it at their own cost. but that doesn't have much to do with the fundamentals of the floating bridge itself.
      - deleted 2y ago
        [deleted]

tiagod 2y ago

Interestingly, the 25 of April Bridge in Lisbon was made by the American Bridge Company, same as the Bay Bridge, but not the Golden Gate. And yes, it's normal. That bridge is very well maintained (there's a whole team there working daily, afaik, and I've witnessed many interventions in the past).

rob74 2y ago
Now that you mention it, the diagonal braces on the piers (no idea how they're actually called) look very similar to the Bay Bridge. But to the casual observer, the number of piers and the color look more like the Golden Gate bridge, plus that's by far the better known one, so I'm not surprised it got this nickname...
- tiagod 2y ago
  I agree, and it's a very common misconception among locals that it's related to the Golden Gate bridge

BurningFrog 2y ago

Depends on the bridge type, I guess. But it's true that big structures are often designed to move as a way to deal with forces. It's much better than something firm that doesn't move until it snaps.