Some related info here:
According to the wikipedia entry:
David McCullough’s The Great Bridge is a terrific book about the designers, builders, financiers and the difficult and dangerous process of building the Brooklyn Bridge, BTW. Well worth a look.
Actually, this is an interesting point: what would it take to bring the bridge down?
Seems to me that if you drove a truck loaded with C4 onto the bridge and set it off, most of the blast effect would be dissipated around the various structural elements and except for some melted asphalt, there would be minimal damage.
So a huge thermite bomb? Maybe a nuke? Godzilla???
You can probably blast holes the deck with impunity and not bring down the bridge. To really cause some damage you have to make the towers collapse or destroy the anchorages.
Yes, of course; that would be the logical way of doing it.
I was thinking along the lines of the experience of Bomber Command during WWII.
They discovered that just bombing a German factory did little damage outside putting holes in the roof and walls. The internal production facilities were relatively unaffected.
However, they eventually discovered that heat effects distorted and damaged the machinery. These effects were what put the facility out of production.
Consequently, they started to mix their bomb loads: a little high explosive and a lot of thermite, phosphorus, or other heat generators.
So, in the case of the bridge, I would assume an explosive on the deck would have its blast effect directed upwards and outwards, and thereby be dissipated.
The heat effect would be small and of very short duration; certainly not long enough to damage the cables.
I would imagine that the underlying concrete deck would be unaffected; think of concrete sub pens at St. Nazaire. They are still standing despite all the efforts of Bomber Command.
So assuming you wanted to do it the dumb way and park a truck on the deck etc, you would need something that generates a lot of heat for a long time. This would weaken, and possibly melt, the cables.
I’m not saying this thread should be closed, but doesn’t all this talk about how to blow up a vital transportation link give you the willies after 9/11?
Or are we just discussing the conspiracy theories before it happens?
Well, the product of the thread so far has been to place the Brooklyn Bridge on my list of places not to depend on When The Revolution Comes.
Of course, I’m in Norway, so I’ve already checked that box.
As it turns out, The Revolution will require vast quantities of ludefisk. So watch your back.
If a shore-to-shore cable had to be replaced, what would it take to prop up the bridge from underneath while the replacement was being made?
Of course, this is a very valid point. However, that boat has long since sailed.
There are numerous movies and novels that have dealt with this issue, both in the generalities and the specifics. Some of them were referred to in the post noted above and which triggered this line of thought. So it is not exactly a new topic.
Also, while the world’s terrorists may be evil, they are not stupid. So any discussion we have about the topic here is, without a doubt, old news to those who will do us harm.
Not only that, but I have no doubt that they have prepared plans for terrorist acts we haven’t even thought of yet. Prior to the event, how many of us could even have imagined flying a commercial airliner into an office building?
Unfortunately, that is the world we live in.
As far as refurbishing the bridge goes, the OP mentioned that the bridge was built to be four times as strong as it needed to be (designed six times as strong, but in the fine tradition of contractors, sub-standard materials were used). So, in theory, wouldn’t that mean you could remove half of the cables and the bridge would still be able to support its weight?
Granted, since there’s probably not a way to remove half the cables without taking them all from one side, you might need some temporary supports under the bridge, but I’m sure they’d find a way to make it work if it was worth it to them.
Perhaps the best way would be to construct temporary towers and anchor blocks right by the sides of the bridge and then transfer the load of the deck onto the cables suspended on the new towers. Once the weight is being bore by those you could remove the old cable and install a new one.
The cables on the middle of the towers are more complicated, I suppose you could make a hole in the decking and place temporary towers on each side of the tower (along the length of the bridge.
Still a heck of a lot of work though.
I don’t know that you’d need temporary towers. Here’s a good picture of one of the towers. String a new temporary cable over the top of the tower[sup]*[/sup]. The tower would have to bear the weight of that new cable, but it wouldn’t be carrying any of the load from the bridge deck, yet. As you hang new suspenders, the load would transfer from the old cable to the new, temporary one. The tower would only ever have to carry the extra weight of the cable itself. (Still rather a lot, I know.)
The trickier part might be to create an anchorage for the end of the temporary main cable. There’s incredible tension on those; that’s one of the hidden things that really makes a suspension bridge work.
(When Mythbusters tested the marching-on-a-bridge myth, I felt that was one of their true misses. Adam built a beautiful, free-standing suspension bridge. No anchorages at the ends; really missed the point.)
- Unfortunately, the suspender cables would be hanging straight down, directly through the space where you’d be spinning the new main cable. To make room, have two temporary cables, each offset slightly, so the suspender cables would come down in a ‘V’.
During Desert Storm-I I recall them saying that when they wanted to put a bridge out of commission they need to blow up the anchorages at one end or the other. Putting a hole in the middle of the bridge rendered it useless temporarily but was (relatively) easy to fix. Blasting the ends of the bridge pretty much finished it.
Of course none of those were suspension bridges and a suspension bridge’s anchorage is mighty strong so would take some doing to destroy it but doing so would end the bridge.
I imagine taking a tower down would likewise end it but again those are very strong.
Severing one of the main cables would finish it as well but (surprise) it is also insanely strong. If you were trying to melt it you’d need a fire burning a long time and extremely hot…good luck.
In short yes, there are critical failure points for a suspension bridge but the engineers know them well and those points are engineered to insane strength for that very reason.
Even Godzilla would have to wrestle with one (for example twist a paper napkin real tight then try to pull it apart…not easy so I imagine cables such as these could be used for a tug of war between King Kong and Godzilla with no problems).
You really think that the sort of people who want to cause mass panic haven’t thought about this before? That they might somehow stumble upon this thread and then come to the conclusion that the Brooklyn Bridge would make a good target?
Not at all. I just feel funny discussing the possible ways such a thing could happen.
Let’s talk about other ugly ways to kill people and destroy buildings, why not?
Lots of interesting discussion here, but nobody really addressed the OP question about a catastrophic failure. I believe the answer is No, although I’m trading on 20 year-old material science knowledge that I haven’t used since college.
The steel used for the cables will not suddenly snap due to degradation. In the unlikely event that enough of the cable cross-section were compromised completely through, say, corrosion or impact or some nutter with a saw, the remaining steel in the cables would become stressed beyond its yield point, at which time it would begin to lengthen through plastic deformation. (Side note: don’t forget the factor-of-safety of the design noted by others, making this very unlikely.) This would be clearly noticed as a change in bridge elevation. This is one reason why steel is such a great building material; when you stress it too much, it bends, but doesn’t snap (up to a point, obviously).
This is not in any conceivable way a terrorist issue. It is, however, a daily, real-world concern for every single bridge in the entire world. And the decay of our aging infrastrucutre is simply one of the most important issues in the entire country.
I can’t understand how anyone could advocate not talking about it. it should be front page news daily until we start spending the money to fix the known dangers.
IIRC, when they got around to dismantling the remains of the Tacoma Narrows I bridge, it was discovered there were quite a few snapped strands in the main cables. I don’t recall the percentage.
Also, due to the imbalance of the weight of the side spans versus the now absent main span, the towers were also slightly buckled (outwards).
Considering the thrashing that bridge executed during it’s fatal oscillations (btw, the movie of the collapse only runs 10s of seconds, the gyrations went on for hours in actuality) I am surprised the frayed cables and buckled towers weren’t far more damaged.
Did you know the tower foundations were re-used, and the anchorages were supplemented with more concrete and were reused too?
If I could look into the future, I’d bet that the bridge would fail due to the Manhattan tower falling due to soil liquefaction from the effects of a Brooklyn / Manhattan earthquake.
The Brooklyn Bridge deck needs a good leveling. I doubt it is going to get one, though - that would involve closing one whole side and fixing it. Simply filling in the large dips would add to the static loading on the bridge and wouldn’t be a good idea.