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/306198
The UHPC component was used in the center span. T h e n e w J a k w a y P a r k B r i d g e i n Buchanan County, Iowa, offers great potential for expanding the use of ultra- high-performance concrete (UHPC) in bridge girders and specifically in the new Pi (as in the Greek letter π) girder. By understanding the process used to create the second generation of this girder and leveraging its full capabilities, designers can take better advantage of the properties of this unique material and help reduce costs in future projects. Officials in Buchanan County were granted funding through the TEA- 21 Innovative Bridge Research and Construction Program (IBRC), managed by the Federal Highway Administration, to construct a highway bridge using an optimized Pi-girder section with UHPC. The design, using the second generation of the Pi-girder section, provides the first application of the Pi section for a highway bridge in the United States. The girders are pretensioned longitudinally and tied together transversely with mild reinforcing steel and steel diaphragms. Developed in France during the 1990s, UHPC has seen limited use in North America. UHPC consists of fine sand, cement and silica fume, and quartz flour in a dense, low water-cementitious materials ratio (0.15) mix. Compressive cylinder strengths of 18,000 psi to 30,000 psi can be achieved, depending on the mixing and curing regimen. The material has extremely low permeability and high durability. To improve ductility, steel or fiberglass fibers (approximately 2% by volume) are added, replacing mild reinforcing steel. For this project, the patented mix Ductal, ® developed by Lafarge North America, was used with steel fibers. Iowa was first introduced to UHPC with a bridge project in Wapello County, which was completed in 2006. Wapello County was also granted funding through IBRC for that project. The UHPC mix was used in four Iowa bulb-tee beams that were modified to better utilize the mix. Beam performance was verified by flexure and shear tests on a 71-ft-long profile JAKWAY PARK BRIDGE / BUCHANAN COUNTY, IOWA ENGINEER: Iowa Department of Transportation, Ames, Iowa CONSULTING ENGINEERS: Buchanan County Department of Engineering, Independence, Iowa; IIW Engineers & Surveyors P.C., Dubuque, Iowa; and Iowa State University Bridge Engineering Center, Ames, Iowa AWARDS: Co-winner of PCI's 2009 Design Award for Best Bridge Project (up to 75 ft span); 2009 Iowa Quality Initiative Structures Research Merit Award from the Associated General Contractors of Iowa and the Iowa Department of Transportation Buchanan County constructs a bridge using ultra-high- performance concrete girders FHWA, Iowa optimize pi Girder by Brian Keierleber, Buchanan County, Dean Bierwagen, Iowa Department of Transportation, Terry Wipf, Iowa State University, and Ahmad Abu- Hawash, Iowa Department of Transportation The Jakway Park Bridge in Buchanan County, Iowa, features the second generation of the Pi-girder cross section made with ultra-high-performance concrete, shown here in the precaster's yard. At the bottom of the beam webs were 7-in.-deep by 1-ft-wide flanges. Each flange contained nine 0.6-in.-diameter strands tensioned to 72.6% of ultimate. Photos: Iowa Department of Transportation. 24 | ASPIRE , Winter 2010 ASPIRE_Winter10.indb 24 12/18/09 2:17:54 PM