BASCULE BRIDGE

bascule is French for a balance beam. That pretty much describes how a bascule bridge works.

Like a see-saw with weights on either side of the pivot point, a bascule bridge consists of the weight of the movable part of the bridge- the deck- on 1 side and the other movable part ( including the counter-weight) on the other side.

This is the 3rd st bridge in San Francisco with the “leaf” in the raised position. The leaf weighs many tons

and it would take even more tons to raise it .

Do you see that grey concrete block hanging off the end of the bridge?

Here’s a better shot. All that weight balances the weight on the other side- the leaf.

Of course there’s a motor too, but it doesn’t have to be a very powerful motor,

since a lot of the force needed to lift the bridge comes from the concrete counter-weight.

Here’s my take on a bascule bridge.