ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306183
Restored in 2007, the Rainbow Bridge on State Highway 55 over the north fork of the Payette River is on the National Register of Historic Places. 40 | ASPIRE , Spring 2011 S TAT E S TAT E A long with many other states, Idaho f a c e s c h a l l e n g e s i n m a n a g i n g i t s bridge asset s by cost effectively ex tending t h e i r s e r v i c e l i fe o r r e p l a c i n g t h e m . Fo r bridges with spans of less than 130 ft, the need for economical, durable, and quickly constructed bridges usually makes prestressed c o n c r e t e t h e f i r s t c h o i c e . I n n o v a t i v e options, especially with accelerated bridge constr uction (ABC) techniques, also have proven to work well with precast concrete. Precast, prestressed concrete bridges have become Idaho Transportation Department's (ITD) first choice for a variety of reasons, particularly because they usually provide the lowest first-cost solution. But they also offer low, long-term maintenance cost s due to their high durability. They provide flexibility, offering many cross sections to choose from and providing a range of ways they can be used. Precast concrete bridge component s are readily availa ble in the state, and several fabricators regularly supply products. In some cases, for bridges with spans under 30 ft, ITD uses cast-in-place or precast concrete box culverts or three-sided structures. Generally, the ITD under takes 50 to 60 bridge projects each year, but they vary widely in their scope. Only about 10 of those projects a r e c o m p l e t e r e p l a c e m e n t s f o r e x i s t i n g s t r u c t u r e s . T h e r e s t a r e r e h a b i l i t a t i o n s , widening, and upgrades of all types. Keeping the existing bridges accessible and functional is a key part of the work. Rainbow Bridge Restored An example of rehabilitation work is the State Highway 55 Bridge over the north fork of the Payette River. This structure, known as the Rainbow Bridge, is a 411-ft-long, open-spandrel, cast-in-place concrete arch bridge. Built in 1936, it is now on the National Register of Historic Places and has become well recognized in the state. It's definitely considered a keeper, and great efforts have been taken to preserve its structural integrity. In 2007, it was completely rehabilitated. Techniques included chloride extraction and the installation of materials to mitigate corrosion in the future. A few components were replaced during the work, such as the end portion of some stringers. Also, the existing railing had deteriorated, so it was demolished and a precast concrete railing replaced it. As this design had to perfectly replicate the original, it was fabricated in a precast concrete plant and shipped in segments to the site to provide better control over its character and quality. All of the work was done in stages, to allow vehicle access to the bridge throughout the construction. The local office of CH2M-Hill assisted ITD with the restoration project. Snake River Bridge Completed At the other end of the spectrum on bridge construction is the new U.S. 95 Spur over Snake River near Weiser, Idaho, which was completed in 2010. The $10-million project replaced a bridge originally built in 1950, providing wider lanes (a total of 46 ft 4 in. versus 30 ft 6 in.) and capable of carrying greater traffic volumes. The 876-ft-long bridge features six spans of precast, prestressed concrete girders comprising 144 ft-long, 84-in.-deep, modified bulb-tee Spanning the paSt and Future Idaho Looks to Preserve Existing Bridges while E xpanding Capabilities for Ne w Structures by Matthew Farrar, Idaho Transportation Department The I-84 Ten Mile Interchange in Meridian, Idaho, features a 189-ft single-span, cast-in-place concrete box girder. A single-point urban interchange (SPUI), the post-tensioned design provided cost effectiveness and constructability at the complex site. State_Spr11.indd 40 3/30/11 5:17 PM