One option that the City of Ottawa took to replace an overpass of the city’s main highway was to close the highway for a weekend, tear down the existing overpass and then replace it with essentially a pre-fabbed one. They had to work day and night to do it, but it supposedly ended up being cheaper than the normal option because trying to replace the overpass with the highway open would have taken months and racked up huge labour costs.
I suspect that’s not a technique that is useful for crossing a river, though. The span of the prefabbed bridge is probably quite limited.
I found a youtube video describing the project. The technique is called rapid bridge replacement.
This was more or less what was happening with the Lake Washington floating bridge (I-90) when it sunk.
They built a second bridge next to it, moved traffic from the old bridge to the new bridge, then closed the original down for repairs and renovation. The repairs did not go as planned.
The Skagit River Bridge that collapsed last night was most likely hit by an oversized truck carying a massive drill rig, causing one of the spans to drop into the Skagit. All indications so far are that the rest of the bridge is in good condition, and that the piers are OK too. The State is now in the process of trying to find several Bailey Bridges, and if the first two indications are correct, these could be used as a fast temporary fix until the collapsed span could be replaced. As of right now, they haven’t been successful in the search, but I can’t believe that, on all the Army posts in this country, there aren’t a few Bailey’s stored away. As these are IIRC designed to carry a main battle tank, they should be perfectly OK for a temporary repair.
Buffalo has one of the best methods, for the new Signature Bridge across the Niagara in and out of Canada. If you never are able to decide on either a design or a location, you never have to spend the money.
Moving the customs area to an open area in Canada, then preventing vehicles from leaving the road while they pass into the US would make the need for a new bridge go away, but that would be too easy. They must be waiting for some old guy, like Cuomo, to pass so they can build a bridge and name it for him.
The temporary bridge need not last 80 years. It only has to last while the permanent bridge is constructed. The temporary bridge can be modular such that it can be dismantled and re-used elsewhere. It’s more like one bridge for the price of 1.2.
For a biggie, see the SF-Oakland replacement. This was the bridge which developed the “trap door” during the Loma Prita (1989) quake.
New bridge taking a slightly curved arch and meeting at the end (Treasure Island).
Any method you can think of has been done - it is simply a matter of options.
In the SF-Oakland case, the old bridge was moved 6" north by the quake - untold damage to the entire structure meant it would not be repaired (they thought they could build a new one cheaper. The problems they’re finding may mean they will need to build a third (structural issues with the concrete in the supporting structure).
They replaced a bridge near me recently (North Avenue bridge over the North Branch of the Chicago River near Goose Island). They built a temporary bridge adjacent to and just south of the original bridge, and traffic went in a big bow around the old bridge while they rebuilt it. But I think they incorporated the temporary one into the design of the new one, because when construction was finished it was much wider than it had been. No bends or kinks remained, though.
A little off-topic, but there is a bridge in Richmond, Vermont, currently being rebuilt. The bridge, across the Winooski River, a fairly sizable waterway for that part of the world, has a high arched lattice superstructure. It was very narrow, and in a sane state would have been torn down and replaced.
However, it does has some historic value, so They decided to rebuild it instead. The amazing thing is that they widened it at the same time. The latticework was split, the two halves pulled a dozen or so feet apart, and new steel installed to fill in the gap.
The day they pulled the halves apart, I saw it on the news. Most jaw-dropping thing I’ve seen in a long time.
One of the techniques I have seen on major roads is to begin building a new bridge right alongside the old bridge, adding the width of an extra lane. Then as that lane is finished they close off the lane on the old bridge right next to it, divert the traffic from that lane onto the new bridge, demolish & rebuild that closed lane, and repeat the process until they reach the center of the bridge. Often they do this on both directions at the same time. As a result they end up with a bridge now completed without ever having lost a lane during construction and it now has an extra lane in width, which could be used as a breakdown lane or as an extra lane if the highway is to be widened anytime soon.
Also when the time comes to rebuild the bridge again the extra lane is already in place for construction crews to work with.
Generally this technique is used for smaller bridges such as overpasses for interstates over roads and creeks, not larger spans.
They just recently added a second span to the Tacoma Narrows bridge (“Galloping Gertie”), but I am no aware of any plans to demolish the old span. The mismatched towers side-by-side makes a pretty ugly sight.
That’s not uncommon. You have an existing bridge well within its life that is working well, but traffic has grown and the existing bridge is narrow. Add a new bridge in parallel, route one direction on the old bridge and one direction on the new bridge. Instant doubled lanes. The old bridge isn’t replaced until it reaches end of life.
