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Wednesday, May 4, 2016

Cherokee company's crew builds one-of-a-kind bridge

Wednesday, March 15, 2006

The Ravenna Bridge at night.
When Scott Christensen and his crew , from the Cherokee-based company Christensen Brothers, Inc. , took on the job as Prime Contractor to build a new bridge in Ravenna, Neb. (a little NE of Kearney), they entered into one of those situations where, says Christensen, they had to "invent ways to solve new problems as they came up."

Christensen and his crew had many years of experience building bridges throughout Iowa, Nebraska, South Dakota, and Kansas, but the project they were tackling brought up a lot of new problems for a good reason. The steel tied-arch bridge, built over the Burlington Northern-Santa Fe Railroad tracks. is u the only bridge of its kind in the world.

What makes the bridge unique is that the upper tubes and lower tie beams of each arch are filled with 8000 psi self-consolidating concrete, which the crew pumped into the tubes and beams. The lower tie beams each have two post-tensioned steel strand tendons (19 steel strands per tendon); and the concrete bridge deck has 64 post-tensioned steel strands. The unique design is the combined effort of the Nebraska Dept. of Roads (NDOR) Bridge Division and the University of Nebraska College of Engineering. Dr. Maher Tadros of UNL created the concept for the design, and the actual design effort was a collaboration between the lead designer for NDOR and Dr. Amgad Girgis of UNL.

Christensen and his crew worked on the project for thirteen months , returning to their homes on most weekends.

The new bridge replaced a viaduct which was built in 1936-37. Normally, existing structures are completely removed before construction of a new structure begins. On this project, though, something new was tried. The crew used the existing bridge as a staging area to erect and set the two tied-arches on the abutment columns. The existing deck areas were also used as a platform for removal of the existing deck, and to place the steel floor beams between the arch segments.

The bridge opened in November 2005. Though there was a short period of time when traffic on Highway 68 had to take a detour, the trains were able to run continuously.

All the work is done on the project, except for the painting, and this will be done in May. The arch tubes and tie beams will be painted blue and the hanger rods will be silver , blue and silver being the school colors of Ravenna High School. The MSE walls and concrete barriers will receive a stain finish.

Christensen Brothers , Inc. was the prime contractor for the $4.3 million dollar project, and sub-contracted the various different aspects of the project. Christensen was the project manager and Wade Christiansen of Schaller served as foreman of the crew. Christensen says his normal crew was usually around seven people, but they expanded to 14-15 for certain aspects .of the project.

The Project Manager for the Nebraska Department of Roads was Kirk Weber, NDOR had three inspectors at the site as well.

Christensen Brothers was founded by the great-grandfather of Scott, Duane and John Christensen, Soren Christensen, about 80 years ago, and the business has operated continuously ever since. Their primary business these days is in building bridges, but they do some general construction work as well.

Scott Christensen says one of the amazing things to him about the Ravenna Bridge Project was that they built the steel reinforcing cages in Cherokee, then hauled them to the site in Nebraska, one at a time, on stretch trailers. Each cage is 60 feet long, 8 feet in diameter, and weighs 20 tons !

A photographer from the Ravenna newspaper was at the site every day during the 13-month project, and she is responsible for the photos of the project which accompany this article, as well as many other photos which Christensen has.

Though the painting has to be finished this spring, Christensen Brothers will receive the Biennial Bridge Construction Achievement Award in Kearney, Nebraska on March 16. They were also winners in 2004, for the construction of the only "electric bridge" in the world, in Roca, Nebraska, a suburb of Lincoln. This bridge melts ice, and was the subject of a Discovery Channel report in February 2004. The states of Wyoming, Iowa, and Utah have shown interest in having "electric bridges" built in their states also.

Cherokee should be proud of the Christensen Brothers business, just one of the Cherokee businesses which have established solid reputations throughout the world for their quality work.

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