1 Joule heats 1g water 0.24 C

1 L water == 100g

1 cu.meter water = 1000L

Room Temp == 23 C

Thus:

(77/0.24) = 320.8 Joules raises 1g water from 23 C to 100 C (boiling).

(1E9 Joules / 320.8 Joules) lightning strike with no losses along the way heats 3,116,883g of water.

3,116,883g of water == 31,168 L of water == 31 cu.meters of water. This is a block of water 1m x 3m x 10m.

Steam volume is 1600x liquid water volume. So even if we say that 90% of the energy is lost in the transfer, that's still 3 cubic meters of water that flash-boils into steam, quite possibly causing damage to the bridge.

So: perhaps unlikely, but quite possible.

Edit: 3,116,883g of water == 3,117 L of water == 3 cu.meters of water. Damn math errors, always creeping in. Still unlikely, still possible.