The bridge that collapsed last night was 57 years old, and I now understand that there has been talk of replacing it. This thread is not about that particular bridge.
How does one go about replacing a bridge over a major road?
[ul][li]Build a new bridge next to it, and use the old bridge until the new one is done? But that would result in an offset to the freeway. [/li][li]Build a temporary bridge next to the old bridge, replace the old bridge, and then tear down the temporary bridge? That seems wasteful, as the temporary bridge would have to be strong enough to handle the loads until the new bridge is finished. You get one bridge for the price of two. At least you wouldn’t wind up with a jog in the road.[/li][li]Depending on the type of bridge, build new bridges on either side of the old bridge, using the old bridge until they’re done; then open up the ‘outrigger’ lanes and replace the old bridge with a new one that conforms with and is ‘blended into’ the ‘outriggers’? That makes for more lanes, but they might not be needed.[/li][*]Choose an end and build half of it, then build the other half? No, wait… That wouldn’t work. [/ul]
There’s a major thoroughfare in my neighborhood that crosses a creek, and that bridge is scheduled to be replaced soon. During construction, traffic that normally takes the highway north or south will be shunted to a detour that crosses the creek slightly upstream or downstream. Similarly, the hiker-biker trail that crosses the highway at that creek will be rerouted to cross the highway slightly north of the intersection.
It depends.
Can the road be closed while the old bridge is demolished and rebuilt?
Is there space next to it to build a permanent bridge?
Can one side of the bridge be rebuilt at a time?
Is the span short enough so a temporary bridge can be built.
Temporary bridges just need to last just long enough, so it’s not double the cost, some use heavy timbers or stock pieces of steel that can be reused, etc.
The bridge that collapsed last night was 57 years old, and I now understand that there has been talk of replacing it. This thread is not about that particular bridge.
How does one go about replacing a bridge over a major road?
[ul][li]Build a new bridge next to it, and use the old bridge until the new one is done? But that would result in an offset to the freeway. [/li][li]Build a temporary bridge next to the old bridge, replace the old bridge, and then tear down the temporary bridge? That seems wasteful, as the temporary bridge would have to be strong enough to handle the loads until the new bridge is finished. You get one bridge for the price of two. At least you wouldn’t wind up with a jog in the road.[/li][li]Depending on the type of bridge, build new bridges on either side of the old bridge, using the old bridge until they’re done; then open up the ‘outrigger’ lanes and replace the old bridge with a new one that conforms with and is ‘blended into’ the ‘outriggers’? That makes for more lanes, but they might not be needed.[/li][li]Choose an end and build half of it, then build the other half? No, wait… That wouldn’t work. [/ul][/li][/QUOTE]
All of those techinques can be used at one time or another, it depends on the situation.
There was a major freeway widening project in my area about a decade ago, and all the bridges crossing it had to be replaced. Mostly they used the first technique, which means that all the bridges now in use have a slight curve to them as they cross the freeway.
The Oakland-San Francisco Bay Bridge is doing the first option right now (well, only half of it; the bit between Treasure Island and Oakland). They’ll presumably have to change the curve of the road just before the bridge, but given that this project has take years, I don’t think closing the original bridge was an option.
They’re replacing the Tappan Zee Bridge right now. They’re going with Option 1. The new bridge will be built parallel, and the highway will be moved slightly for the new approaches.
They are replacing a bridge in Portland now, and they are going with a 5th option - actually shifting the current bridge over a bit then building the new one in the original position. The engineering needed is pretty cool. Here’s a time lapse video of the move.
On my commute into work, they are rebuilding the Central Ave. bridge over I-55 in Chicago. They are not using any of the above options.
It was originally 4 lanes, 2 lanes each going north and south. They forced it to one lane in each direction, on what had been the south-bound lanes, and rebuilt half of the bridge, including the exit and entrance ramps on that side. Then they moved traffic to the side they finished and tore down the other half of the bridge.
All this time I-55, a major artery in to and out of Chicago, kept 3 lanes of traffic running during rush hour - though they had some lane closures during off-peak hours and weekends. They did reduce the size of lanes through there and lowered the speed limit 10 mph as well.
It’s been very interesting to watch on a daily basis. I actually hope for traffic through there just so I can see what progress has been made. Oddly enough, that is usually one of the fastest stretches of my commute.
I concur that the roughly 5 replacement bridges I’m familiar with are offsets.
Look at it this way, when the offset bridge eventually needs to be replaced, they can build the new one in the original’s place!
I’m also familiar with a case of a new bridge built alongside the old one simply because of the need for more lanes. About a decade later, they demolished the old one.
This one depends on the condition of those pilings. They could replace the bridge sections pretty quickly if the supports are still good. Since those are likely to have deriorated over time that’s probably not a long term solution, but they could make temporary repairs to the current structure and start a new bridge next to it.
Another option, which was carried out in Rogue River, Oregon (near where I grew up), is to build a new bridge right next to the old one, tear the old bridge down, and then move the new bridge into place.
I wish I could find a cite but I am having trouble at the time. It seems impossible but I swear that’s what I remember. If anyone could substantiate my claim, I’d appreciate it!
This is what most frequently happens here. Let’s say the old bridge had 2 lanes in each direction (4 total). They build another bridge right beside it with 4 lanes total. They then move traffic to the new bridge and rebuild the old bridge. They then have two bridges (in the same location so functioning as one) one for each direction of traffic with twice as many lanes.
There’s a bridge not far from my house that is sort of in the process of being replaced. They went with option 2 - they built a “temporary” bridge next to the old one, with the promise of tearing down and replacing the old one. But it’s been something like four or five years now since the “temporary” bridge opened, and the old one is still there, untouched. Budgets got all screwed up when Hurricane Irene wiped out several dozen bridges in the area that had to be rebuilt more urgently.
A bridge on one of my local streets was an old single structure construction. When they tore it down and replaced it, they just closed the road.
Many do the “build a new bridge next to the old one, then rebuild the old one, and have two bridges running side by side, making double traffic lanes in each direction”.
When Houston closed the Baytown tunnel they replaced it with a bridge, and redirected the road to match. That’s fairly common.
Do the “shunt traffic over, rebuild 1 side, then shunt traffic other way, rebuild the other side” technique. Especially allowing widening.
Hadn’t heard of moving a bridge over before. Interesting.
Sometimes the answer is, shut it down and have everyone take a different route.
We had a major interstate bridge collapse in Minnesota 6 years ago, right in downtown Minneapolis, crossing the Mississipi river (so limited side streets).
A collapse is different than a planned replacement, because using the old bridge just isn’t an option. Here, they rerouted all of the traffic to a couple of other highways/limited access roads. They actually upped the number of lanes on the detour roads, by narrowing the lanes and the shoulders and just painting in an additional lane. Additional bus routes were added to help move people.
The other thing they did was throw a whole bunch of money at it. Construction was completed a year later, 3 months ahead of schedule. The construction company got about a 10% early completion bonus, although I’ve heard that a lot of that went to paying overtime.
On a bunch of interstate bridges in higher traffic areas, there are already two separate bridges, one for each direction - they build crossovers and split the bridge for one direction into a bridge for both directions, rebuild the empty bridge, then cross all traffic onto the new bridge, and rebuild the other one.
A quick fix is to get a ferry setup. That’s assuming the state highway dept has any they can spare. Ferrys can’t handle the volume that a bridge can. But they can help while a bridge is rebuilt.
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