In Thursday’s new X-Men: Apocalypse trailer, people with symmetrical faces wax urgent about the end of the world. Because no doomsday scenario worth its salt would pass up smashing urban infrastructure, we get to see yet another suspension bridge demolished (a betentacled explosion at the 01:27 mark). Hollywood loves to break bridges, but it almost always gets the devastation wrong, as New York structural engineer Alex Weinberg points out. Does the new X-Men redeem the civil engineering implausibility that is Magneto’s bridge-lift at X-Men 3’s end?
Suspension bridges are the structural redshirts of the kaiju/disaster/superhero triumvirate that dominates blockbuster Hollywood. As it goes with the Star Trek scrubs, if you see one, there’s a good chance it won’t make it to the credits. (See: Cloverfield, Godzilla, The Dark Knight Rises.) What better way to couple epic destruction with strategic supply-line cutting? It might make for good movie magic — but that doesn’t mean the physics of it also make sense.
Here’s why none of those scenes could actually happen:
Cables between towers literally suspend (as their name suggests) the bridges above water, and terminate in points called “anchorages”. As weight pulls downward on the cable, the tower-anchor combo makes the system surprisingly resilient for how light it can be. Though the cables of the Tacoma Narrows Bridge didn’t give out in its 1940 collapse, destruction in the center also caused damage on the butt end — you can see the tension relax in the back and smash down on cars. (PBS has an experiment involving textbooks and twine, if you want simulate this at home.)
But when cables are severed, the end result is pretty much what you get at, say, a ribbon-cutting ceremony — which is to say the whole shebang comes crashing down. Total collapse, notably, doesn’t happen in X-Men 3, when Magneto extrudes the Golden Gate Bridge from its anchor points and the stretch of road remains intact.
Does X-Men: Apocalypse fare better? It’s not quite clear. As Weinberg tells Inverse, “Unfortunately there just isn’t enough for me to judge either way. Clearly, some kind of supernatural upward thrust damages the Manhattan Bridge.”
We can see a cut through the road deck, but the combination of smoke, water vapor, and magic obscure the main cables.
“So those crucial structural elements may very well still be intact,” he says. If they’re not, well, the whole road ought to fail, catastrophically.
Suspension bridges might die all the time in Hollywood, but the least we can do is give them the dignity of physics.
For more on the cinematic destruction of suspension bridges, check out Weinberg’s post on Hackaday.