[creata]

Yeah, this is the only one that seems flat out wrong. When I'm on a bridge, I absolutely want to see "The bridge can hold up 3000 kg", NOT "The bridge can hold up 29 kN". Partly because "holding up" (as opposed to, say, withstanding) force sounds nonsensical, but primarily because knowing the maximum load in kg is much more useful.

[nayuki]

Structures like bridges are a complicated case because you can't describe its load capacity as a mass or a weight (force).

I'll assume that a bridge fails when the downward force on its deck exceeds a certain constant number. But that force is inclusive of the dead weight of the bridge.

Let's say a bridge has a mass of 1000 kg and it can hold up an additional 1000 kg of vehicles on Earth. That means it can hold up about 20 000 N of weight (assuming that g = 10 m/s^2).

The Moon's surface gravity is 1/6th of the Earth's. 20 000 N of weight would be 12 000 kg of mass on the moon. Subtract the bridge's mass of 1000 kg, and you can put 11 000 of vehicles on the bridge - which is substantially more than 6× the mass of vehicles allowed on Earth.

[isoprophlex]

You never know! Tomorrow that bridge might be on the moon, and how on earth (or how on the moon, indeed) will you know if it will hold up when you walk your herd of elephants over it!

[kelnos]

I mean, that's still fine? The max load of that bridge on the moon will just be a different, higher value in kilograms. Since we don't move bridges between planets, it's fine to not advertise a universal value that applies everywhere.

(I get that you're joking, but still...)