THE CONCRETE BRIDGE MAGAZINE

SUMMER 2007

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.

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Reinforcing steel and post-tensioning ducts in a haunched slab bridge. 40 | ASPIRE , Summer 2007 Department of Transportation officials in Kansas have become big believers in the use of concrete haunched slab bridges. The state has approximately 25,500 bridges, with about 5000 on state highways, and concrete haunched slab bridges comprise an extensive inventory in that number. "These three-span structures work very well with the topography in Kansas, and our numerous stream crossings," explains Loren Risch, Bridge Design Engineer. The Kansas Department of Transportation (KDOT) previously had standards for reinforced concrete haunched slabs with center spans from 39 to 72 ft, using 4000 psi compressive strength concrete. As the center span length was limited to 72 ft, the design could only be used for shorter stream crossings. Subsequently, a consultant developed new standards for post- tensioned, haunched slab bridges that extended the span range to 92 ft in addition to providing a high performance bridge superstructure. The longer spans fit very well with the wider stream crossings, says Risch. In creating these designs, KDOT followed the lead of Sedgwick County, one of their larger counties, which started using these bridges two years earlier. This was mentioned in the Spring 2007 issue of ASPIRE. ™ Standard Plans developed The slab soffit features a parabolic profile with minimum depth at midspan and maximum depth at the pier. Longitudinal post-tensioning tendons are draped in a parabolic profile and provide the primary reinforcement to carry the loads. A nominal post-tensioning using straight tendons in the transverse direction is provided for distribution of loads and confinement. Nominal reinforcement is provided in both directions in the top and bottom of the slab for temperature and shrinkage stresses as well as to assist in the positioning of the post- tensioning ducts. Concrete design strength is 5000 psi. State officials liked the benefits of post-tensioned, haunched slab bridges and produced their own designs by Stanley W. Woods Kansas Standardizes Concrete Haunched Slabs ASPIRE_Summer_2007.indb 40 5/15/07 11:43:50 AM

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