A Civil Engineering Success

Civil Engineering History and Heritage

U.S. 20 Iowa River Bridge

The Iowa River Bridge on Highway U.S.20 was built in such a way that it not only was able to expand the once two lane blacktop roads into a four lane highway, but also to keep environmental impacts of construction and existence of the bridge to a minimum.

The $21 million dollar bridge consists of two 12.0 m wide deck structures that each contain five spans of 92 m. These deck structures are made from erecting a weathering steel I-Girder superstructure. "Each deck structure will consist of a 230 mm concrete slab with a 38 mm low-slump concrete wearing course supported by a system of four 3450 mm deep I-girders spaced at 3600 mm centers"(1). The support for these structures will be cast-in-place reinforced concrete substructure units. These units consist of two column bents ranging in heights of 20 m to 38 m, and are founded on drilled shafts or driven H-Piles.

Engineering Success

The construction method used on this bridge is the first of its kind in the United States on a steel I-girder highway. The bridge was constructed by a launch erection method in order to avoid damaging its surroundings. This method allowed for large steel portions of the structure to be assembled on large rollers behind one of the bridge abutments and then pushed from pier to pier with the use of hydraulic thrusts (or pulling with motors and cables). This area is one of few woodlands left in Iowa, and by doing intensive research Engineers were able to obtain their goal while leaving as much of the natural surroundings unaffected as possible.

Lessons Learned

As stated earlier, this was the first use of this construction method and therefore a lot of lessons came from this erection of this bridge. Among these were mostly