This is a representative drawing from the City-commissioned engineering report: there's a similar diagram for each of the 15 sets of timbers.
As you will see if you come on tomorrow's tour, nearly all of the vertical timbers ("piles") are fine -- they're like oversized telephone poles and just as sturdy. (A few piles need patching: the document describes how to place sandbags in the creek to make a small and localized dam while the repairs are made.)
Most of the bolts should be replaced.
A number of the "sashes" and "braces" need to be replaced: just swap them out with new boards when the bolts are replaced.