The 1925 Bridge and the Warren Truss

The 1925 Bridge and the Warren Truss. . , Saint Anthony Parkway Bridge (1925), in 1926., Diagram of a Truss Bridge, Lattice-webbed top-chords on the St. Anthony Parkway Bridge. (D. Pratt, HAER, 2012), St. Anthony Parkway Bridge. (D. Pratt, HAER, 2012), Blueprint construction drawing for the St. Anthony Parkway Bridge, 1925., The Warren Truss , Engineers must consider many factors in new bridge design, including span lengths, materials, form, and context. Bridge form encompasses many types of beam and girder, suspension, and arch and truss types. A truss is a structure whose members are subject to axial compression and tension, but not bending movement. The most common truss types are Warren, Pratt and Howe. Each type has different structural properties. The popular Warren truss was patented in England by James Warren and Willoughby Monzani in 1848. Examples of this bridge truss type can be found worldwide., Northern Pacific (BNSF) Railroad Bridge, 1884, in the vicinity of 17th Avenue N.E., The Warren truss contains a series of equilateral triangles. Truss bridges are constructed so that the floor beams that support the load are attached at the vertices, or points, of the triangles and use the rigidity of the frame to stay in alignment., A Pratt truss has diagonal members (except the end diagonals) that slant down towards the middle of the bridge span., Wisconsin Central Railroad Bridge, Nicollet Island to Boom Island, 1901. Now in pedestrian use., A Howe truss has diagonal members that slant away from the middle of bridge span. The members of the truss are chords, verticals and diagonals and they act only in tension or compression., First St. Anthony Parkway Bridge, 1911.