The new North Avenue Bridge will stretch 420 feet from anchor block to anchor block and will be 78 feet, 6 inches wide. It will consist of three segments — a 252-foot-main span and two 84-foot approach spans. The middle portion of the center span over the river will be supported by suspension cables and hangers, and the remainder of the center section and the east and west approach spans will be supported by cable stays (a total of 24) arranged in a fan or semi-harp configuration.
Both of these systems share two sets of 67-foot-tall support pylons (which rise 50 feet above the deck) constructed of built-up rolled steel plates. The pylons — each weighing approximately 95,000 pounds — are extremelycomplex, since they are required to support the combined forces of the suspension and cable-stay systems. Each pylon foundation is supported by 10 micropiles extending 90 feet into bedrock.
The cable-stayed and suspension systems will work together to support a post-tensioned bridge deck that also acts as a strut to transfer the horizontal loads of the systems to the massive anchor blocks at either end of the bridge span. The bridge deck is being post-tensioned and constructed with 10-inch high-performance concrete to provide greater durability and strength characteristics. And once all the bridge spans are in place, a 2-inch latex overlay will be placed over the entire deck, according to Morcos.
CDOT says the configuration of the hybrid cable-stayed/suspension bridge allows for an open, airy bridge. It also creates the maximum amount of clearance over the river, as required by the federal government. At a little over 18 feet, the new bridge will have the same clearance as the movable one it replaces.-Building Design + Construction (web page)
- See more at: http://www.bdcnetwork.com/reconstructing-chicagos-north-aven...