The lift bridge that crosses the canal at Adams Basin was completed in 1913. The technical name of this type of bridge is a mouthful: Warren pony truss towerless lift bridge. Warren bridges use equilateral triangles to spread out the load on the bridge. “Pony truss” refers to the fact that there are no braces across the top of the bridge framework. (This is curious term. I’d like to know where it comes from.)
But the operative word here is “towerless.” This bridge is one of 16 similar bridges constructed along the western section of the Erie Canal in the early 1900s. Unlike traditional lift bridge designs, they do not use towers to lift the roadbed. Instead, the machinery is contained in concrete-lined pits on either side of the bridge. Two 12-horsepower electric motors are sufficient to raise and lower the bridge. The heavy lifting, so to speak, is done by counterweights and a system of cables that ensure that all four corners are raised and lowered at the same rate.
These may the first such bridges ever built, and they are virtually unique. Designed by a team of anonymous New York state engineers, the bridges’ durability and reliability are attested to by the fact that almost all are still in daily use.
Precise scale drawings of this particular bridge are not available. But they do exist for similar bridges and can be adapted. The bridge model is based on those as well as photos and a few direct measurements. [Note added Sept. 10, 2021: Actually, the original construction diagrams for this bridge have been preserved at the New York State Archives in Albany. I didn’t know this when this post was originally published.] The piers are built first and placed in the Terragen scene (above) to check the scale.
The bridge model is built in Maya and is highly detailed. Here is an unshaded version of the model, rendered in Maya. Below, two views of the shaded model in place and rendered in Terragen.
