Perhaps I missed it a little detail while reading, but how exactly do they get the bridges over the chasms?

I know that Dalinar's chulls pulled the bridges in a vertical position and then the bridges were lowered.

Otherwise, I kept reading about how the bridges were "pushed" into place. How does that work exactly? Considering how often they were described as being so heavy (at least two dozen men needed to carry them), if they were pushed, wouldn't the leading end just fall down into the chasm? Also, I don't recall them being set vertically and then lowered by the human bridge crews. And the certainly weren't thrown across the chasm.

I really enjoyed the book otherwise, but this just nagged at me throughout.