[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.