Kuehl and Payer, Ltd. Engineering in Storm Lake, Sac City and Algona Iowa

Bridge Over Mill Creek On Old 21 Cherokee County, Iowa

The Challenge

Cherokee County wanted to replace an existing high truss bridge over Mill Creek that was on a poor horizontal alignment. The existing bridge had sharp curves on both approaches and had a posted weight limit. There was an approximate right angle between the east west road on the north side of Mill Creek and the north south road on the south side of the crossing. Previous preliminary plans had a new bridge on a straight segment between two horizontal curves. Transitions for super elevation into and out of the curves still made the horizontal alignment marginal in terms of minimum design parameters.

 

The KPL Solution

The replacement bridge was designed on a horizontal curve with superelevation built into the bridge cross section. The length of curve was increased to allow the required superelevation to fall within required design standards. An IDOT standard three (3) span prestressed concrete beam bridge was modified and adapted to fit the horizontal and vertical alignment. The spacing of the straight line beams was adjusted in each of the three (3) spans as were the angles of the two (2) abutments to fit the superstructure to the curved footprint of the bridge deck.



Results and Benefits

The adaptation/modification of a standard design allowed the contractor to use readily available standard beams. The substructure—piers and abutments—were also modifications of standard plan details allowing forming with commonly used materials. Once constructed, the bridge was used to move material from a cut section of the south side of the bridge to the approach fill on the north side of the waterway. The previous high truss has been retained as a historical structure and a canoe access with a parking area was constructed along the south bank of Mill Creek.

 

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