North Canadian River Bridge, Oklahoma Co.

This three span modified Parker truss bridge was built in 1925 to carry Britton Road. It appears to be of state-standard design.

Below, view through the bridge looking east. Each 7-panel span is 140 feet in length

Above, a close view of the middle span. Visible are the extra members of the modified Parker truss. These extra members stiffen the compression members, allowing them to be built smaller than would be possible otherwise.

Below, another close view on the deck. Lacing is used in many members of this bridge.

below, a view of the back side of the portal. Only minor injuries were found in the sway bracing.

Elsewhere, however, the injuries were more pronounced....  This badly damaged tie was probably involved in the same incident that battered the latticed guards.

Above and below, results of an accident that show one of the deficiencies of the modified Parker design. The original impact damage probably came on the tie, which pulled the tension diagonal, which, in turn, pushed on the post via the strut.

Above, another view of the tension diagonal for the two previous photos. Any force through loading that would tend to straighten this member out is probably counteracted via the strut by the forces now set up in the deformed post wanting to buckle further under load.

Below, another view of the damage in the same panel as the above. Note guard damage at the lower right.

Above, here is an undamaged panel form another span. The vertical post is braced at its midpoint by the horizontal strut connected to the tension diagonal. The tension diagonal, in turn is stayed by the short diagonal tie. In later designs, all this would be accomplished more efficiently by the use of a K.

Below, a typical upper chord connection.

Below, a side view of the bridge from a neighboring railroad bridge.

Below, and finally, a nice case of tunnel vision looking straight through the bridge. Overall, this isn't a bad bridge, and it is rather unique. As long as it stands, a few people have permanent records of their poor driving for all to see.


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