Portlandjib.com
new bridges
 

I took the same basic structure I used for the crane (see new crane on main page), and made it into a cantilever bridge. For more info on cantilever bridges, click on BRIDGES on the nav page and go to cantilever bridges.

Next comes a lift or bascule bridge. I attached a line to the end of the deck and led this line over a sheave atop the tower and then down to the windlass.  Just like the draw bridges in old movies, when the windlass is turned, the line lifts up the deck of the bridge.

Another way to lift up the deck is with a counter-weight. I attached 2 lines from the end of the deck to the top of a pivoting frame.  Next I added a brick for counter-weight. It takes very little force to raise the bridge deck.