Over the last few days here in the UK, the TV schedules have been full of September 11 retrospective programmes. I expect it’s been the same in the US. I watched one yesterday about the design of the towers and the various factors which led to their collapse.
One question has occurred to me since. As there were two identical towers close together, would it have been possible to incorporate “bridges” at different levels between the towers allowing access from one tower to the other? I realise it might not be practicable but if it was, in future similar designs it should perhaps be considered. Obviously an identical event is extremely unlikely to occur again but in the case of a major fire in one tower, a large number of lives could be saved if people could be evacuated to the other tower.
The Petronis (sp?) Towers in KL, Malaysia, the tallest buildings in the world, are built this way. The walkway is about 75 stories up, IIRC.
How many pairs of enormous skyscrapers can you think of that could use such a system? And given that both buildings collapsed, how much of a difference could such bridges have made last September? It’s an interesting idea, sure, but I don’t know how practical.
The WTC Twin Towers weren’t right next to each other. They were sort of cattycorner to one another. The only way to bridge the two would be to go from corner to corner, and I’m not sure if that would be structurally possible. Also, the Towers each had a load-bearing exterior wall. By inserting a bridge-sized hole you might be reducing the load strength of the supporting outer “skin.”
Unlike the Petronas Towers, the WTC buildings were not exactly side-by-side. They were kitty-cornered, sort of diagonal. The placement had something to do with the wind forces they would have created otherwise.
A diagonal bridge between the two towers would have been wholly impractical, especially with 1960’s building technology (the Petronas bridge, built thirty years later, was an engineering miracle in itself!) Somebody did shoot a tightrope across the gap, though.
The WTC towers would sway a fair amount in the wind. Not a flaw but just the way the structure was designed. That would probably make it impossible to attach them with bridges.
Buildings of that size flex a fair deal in response to wind and other forces; if they could both be guaranteed to flex in the same directions at the same times, then it would be relatively easy to bridge them, but of course that wouldn’t happen and the bridge would be subject to twisting and stretching.
Wouldn’t a rope bridge work though?
(same sound the wind made whipping around the towers.)
No, an unprotected bridge would have been a very very bad idea (in case that was a serious suggestion).
Yes and it has been done with a single tightrope as mentioned above.
Sway could be compensated for by building the bridge with one end on rollers . I’m not sure how much the structure would be effected by cutting a hole in the corner (or more likely the side right by the corner).
It would have ruined the look of the towers though since corner to corner bridges are bound to be ugly. But you do make a good point - if nothing else and emergency evacuation. Perhaps a roof retractable bridge can be stored retracted and extended to the next building incase exit through the tower is not possible.
The bridge at the Petronas Towers is located on floors 41 and 42. See the image in the link for an idea of how high that is. The highest occupied floor in Petronas is 88.