chrisl

I'm still not even convinced there's a boat there at all. It kind of looks like a bit of wind driven whitecap. I spent some time stepping through that video when it first showed up and didn't see it continue to the left across the screen (I guess since it was the bomb...), since I still haven't seen even minimally convincing evidence that the explosion came from anywhere but above the bridge deck. It was a pretty windy night. The videos of the water show a lot of whitecaps, and a huge amount of the splash got blown back over the bridge, and somehow a lot of people are convinced that the light scattered from the droplets is WP. A) There was a ginormous splash and a strong wind, and water droplets scatter light really well, and b) WP would probably leave some serious marks on the asphalt road surface, if not set it on fire (which would have been kind of awesome).

Hitting the port at Sevastopol would be a big deal, but it's a very legitimate target and the message is more "you've made some poor life choices" than it is an escalation.

Are they saying that the "last two points" that could have taken 30 minutes to traverse but took 6 hours are the ones from Midnight to almost 6 am? I think there's a very simple explanation for that that doesn't require the driver to be connected to any conspiracy.

And if they think it's a truck bomb, the inspections they'll have to do for rail and truck cargo to avoid a second one will be like TSA checkpoints from hell.

I've just been mentally factoring in that it's unlikely to built to anything like the standards I'm used to seeing in SoCal. Probably designed with lower factors of safety than we'd see here, underconstrained against earthquake motion, and then contractors skimping on parts and materials, particularly in spots that don't normally have loads on them but are intended to accommodate conditions that are possible during the bridge's lifetime, but rare enough that it won't just fall on its own. A big bomb on the road deck is one of those conditions that's outside the design space, but maybe would have been partly mitigated by good seismic design.

The twin towers was a much more complicated structural setup and they survived the collisions just fine. The heat of the fire weakened the columns and then too many columns started failing to support the floors above them and it collapsed in a domino effect because even full strength floors couldn't support the mass of floors above them piling up. The Kerch bridge is a much more straightforward structure - it's a lot like a Hot Wheels track, with segments defined by the longitudinal beams and a relatively thin web of steel and asphalt tying them together. Each segment is resting across multiple piers and mostly held in place by gravity with some flexible constraints to keep it from cracking due to thermal expansion/contraction and wind. The two decks don't appear to be really tied together - they rest separately on their piers, which are pretty solid (though susceptible to earthquakes and ice), isolated by the bearings that accommodate the expansion/contraction. So very little of the force that went into the outer deck was transmitted to the inner deck through the structure, and it's just the pressure from the shock wave that did moderate damage to the deck and railing. The catch is that there's probably latent damage to at least the nearest bearings on the inner deck. It got enough force to dent and crease it near the point of explosion, so some of that would have been transmitted. It's now one of those roads that you take in a small car because you to make a trip and have no choice, but if they drive a bunch of heavy trucks loaded with tanks and ammo over it, it could have cracks that propagate and fail catastrophically. Especially since it's in a saltwater environment and suffers things like winter and ice. Water is terrible stuff, especially if it can freeze and thaw (which I'm sure you have more experience than you want with). The rail bridge is also suspect - it took the pressure wave broadside because it wasn't shadowed, so there could be some hidden cracks started (or expanded if they were already there). On top of that it had many hours of burning fuel on the steel in multiple spots. That's going to change the steel properties there, and if they just run trains at full speed over it like nothing happened, they could get a surprise later.

If the explosion was close to the deck of the outer road bridge there wouldn't be much pressure load on the inner one. The pressure from the explosion is gong to be mostly parallel to the deck of the adjacent inner road bridge, and the only things that would get it directly are the railings (which were blown over). The side of the inner road deck would be mostly shadowed by the outer road deck, so it wouldn't see much pressure from the explosion and thus not much force (pressure times exposed area) and not get knocked off its bearings. The outer roadway got whacked like a big rectangular drumhead and probably would have been interesting to watch if you could see it without being close enough to catch shrapnel or the shock wave.

Nice. The long beam mounting doesn't really match what it looks like in the pics, but I imagine whoever did it had to guess and wasn't really building a model to analyze its collapse.

Very tiny ones.

I've been thinking of how to model it at home. Hot wheels tracks are too elastic. Basically it's like laying a long thin piece of sheet metal across some supports (chopsticks?)with the ends weakly constrained in the long direction. Then using a spring loaded center punch to bang it off center between the supports. Make sure you wear safety goggles, and maybe gloves if the sheet metal is sharp...

Just a 2kx2k camera, and the data are optically encoded.

That road is probably pretty floppy when you're driving it with the kind of energy a point explosion of a truck bomb (or bigass missile, for Steve) would put in. It's going to both ripple longitudinally and have twisting modes. It could walk/bounce itself off to the side a little and then tumble to get the amount of offset that's there. It also looks like the longitudinal beams sit on small pier blocks on top of the big piers, so it would be tipping off those to one side and could have had enough momentum to tumble as much as it did.

It's 3D data compressed to 2D as a physical part of the data acquisition process, so it's already compressed by the time it hits the detector and lossless compression doesn't reduce the size. You can do lossy compression, but then you can't get the 3D data back.

It's got to have a lot of compression to do that - I take a lot of incompressible video data at 2kx2kx8 bit x 15 fps and that uses half of a GigE pipe for one monochrome camera and spinning drives can't generally keep up with sustained recording - we have to use SSDs to avoid losing frames. The video looking along the bridge very well could be higher than 10 fps frame rate - the frame to frame motion is pretty small for the vehicles, and the resolution is pretty chunky.

We've seen part of that, and it has a big hole in it right at the waterline. It looks like it could be in the righthand lane, but it would be good to see from the road surface side.

Yes. The original shows the bottom ~20% of the lines in the frame saturated when the explosion starts. It's entirely possible for the truck to be intact in the first half of the frame scan (and show that way in the frame) while it's turned into very small parts as the last 20% of the frame is read out. The frame rate and shutter speed aren't terrible for a night-video - the motion is pretty smooth and objects aren't rippled from the line scan. It could be as high as 15 fps - we could work it out backward if someone knows the speed limit on the bridge and the road dashed line marking standards. If we call it 10 fps then there's at least ~120 ms (maybe 220 ms?) where the camera is totally saturated in the original video before the fireball diminishes. And it's complicated by aliasing with the frame rate and compression of the phone used to record the video from the computer monitor.

So the whole problem with the Russian debacle is the fault of Philip Morris and RJR.

Plus the pan on the remaining roadway is dented downward adjacent to the center of the explosion - it happened on top of the bridge. That longitudinal steel beam seems to explain the "crease" next to the dent in the remaining roadway about a foot in from the white line - the thin pan was slammed against the stiff beam. I'd still ride a bicycle across the remaining pavement, and drive inside the lane from the crease in a passenger car, but heavy trucks might accelerate the expansion of some hidden damage and make things interesting.

This picture shows what looks like some deformation of the remaining road bridge deck:

Or could be at the beginning/end where it's back on land with ties and ballast.

Or unwitting person driving a truck full of legitimate explosives with an extra little timed/GPS triggered gift inside. How it was triggered it TBD. But probably the truck, and probably with clean paperwork "official Russian explosives" on the paper not "bad nazi ukrainian explosives" with paperwork that says "washing machines and toilet paper"

Not quite. You're correct that you suspend a bomb 3 feet above the roadway and blow it up, the roadway will reflect the 50% of the energy from the bomb that's going downward back upwards. But all that energy goes downward first, and the roadway experiences a reaction force equal to the force reflecting back up. And the roadway then deforms inelastically, turning a bunch of that energy into bent metal, concrete, and shredded end connectors, and a big splash.

It's a single segment of roadway, or maybe a few that were better connected to each other than the next ones out, like a piece of Hot Wheels track, plopped over several piers. I initially had the impression that they had done single segments to span each gap between piers, but it looks like longer segments that span several. When you slam a hard force down in between two piers, bending it downward, it pulls the roadway longitudinally and yanks the road out of the end connectors. It's why it has nice straight separations at the ends with just some rebar sticking out.

This isn't NYC in October 2001. Russia is actively supplying military materiel across the bridge and you could either stick a triggering charge in an existing Russian shipment or forge a bill of lading for the truck that's something like "10 tons 152 mm HE shells. Pleeze deliver to Nazi Ukrainians through Toobz. From Russia with Love" and then it's not only ok that it's full of HE, but it's *supposed* to be full of HE.

There should be extra likes available on days when the major bridges fall.