Search - NOVA: Super Bridge on DVD

Educational and Impressive!

Loyd E. Eskildson | Phoenix, AZ. | 11/12/2007

(5 out of 5 stars)

""Super Bridge" tells the story of building the new Clark Bridge over the Mississippi at Alton, Illinois, beginning with the pros and cons of various engineering approaches and ending with its opening ceremonies and the demolition of the old and inadequate bridge. Four years and $90 million are required. A cable-stayed span is decided upon - both for its lower cost and improved aesthetics.

Engineers then study a model of the bridge built in a min-river environment located in Vicksburg, MS., learning that their original idea would create currents dangerous for barge traffic. Thus, they decide to modify pier positions and to construct a dike to create a safer environment. The workers average 15 years' experience and a pay rate of $21.50/hour.

Foundations are located 1,000 feet apart within 1/8 of an inch despite dangerous currents, employing cofferdams. Surveying tools measure distance using the time for a laser beam to go out and be reflected back. Extensive reinforcing steel (tons and tons) is utilized in every phase of the construction; each section of concrete must be poured continuously from start to finish. Extensive testing of all materials occurs throughout the project. (My only criticism of the DVD is that it does not tell viewers how the crew handled the problem of under-strength concrete that inadvertently was poured into one section.)

The Missouri lead-in pier had to be located in water too deep for a bottom-lying cofferdam - thus, and intermediate platform was created with extensive support from steel pilings driven in at various angles. Vertical reinforcing steel bars must be spliced with special connectors.

Dangers on the job include heights, cold, long hours (usually only 8, but sometimes as long as 16), and high winds. Unexpected problems include a sunken barge located at the site of one of the support piers, a 500-year flood during construction, and learning that original plans had to be changed due to unforeseen damage to the epoxy-coated cables. Cables were both visually examined after installation for damage incurred, and through test equipment to insure survival after simulated 50 years of traffic while meeting specified loads.

"Super Bridge" generates enormous respect for the skills of both the engineers and workers involved. Excellent material."