“It was a Burr arch truss bridge,” says Robert McCullough ... “The arch and the multiple king-post trusses combined two structural systems to increase support and rigidity.” ...

OLYMPIA, WA - The Washington State Department of Transportation is considering a program to raise the clearance height of some steel truss bridges built from the late 1940's to the early 1960's.

A truss bridge is a triangular assembly of members that act principally in tension or compression, Gasparini said. The design creates a very rigid structure that transfers the load to a wide area.