ASPIRE Spring 08 - Aspire - The Concrete Bridge Magazine

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COUNTYAnnual bridge projects are fairlystandard, except for occasional standoutsThinking BIG in BooneCounty, Iowa by Robert Kieffer, Boone County, IowaBoone County typically constructs onebridge per year based on needs developedfrom our master map, which breaks downstructures by posted weights, number of lanes,traffic flow, and other factors. Our key challengeis that, as a rural county, we have a varietyof roads that aren’t paved, which are used byfarmers with heavy equipment. We also have theDes Moines River running through the county,which requires more complex bridge designscompared to a structure over a creek or stream.Most of the projects that we build consist ofreinforced concrete slabs or precast, prestressedconcrete beams with a cast-in-place concretedeck. We’re in a pretty good area for doingthose types of designs, with a number of bridgecontractors and high-quality precasters withina 100-mile distance of our county. Concrete isan excellent material to work with, because itrequires virtually no maintenance over the years.We typically use standard Iowa Departmentof Transportation bridge designs. We are pleasedthat the designs are being updated to providemore flexibility and reflect concrete’s versatility.For instance, concrete slab beams previouslycould be extended up to span lengths of 125ft, but that has been now lengthened to 150ft. Designs used to be divided into 12.5-ft-spanlength increments, but now they are providedin 10-ft increments. The changes provide moreoptions and help us create greater span lengths.The changes are particularly significant forbridges over water, because the slab bridgesrequire less clearance than concrete beambridges. Raising a slab bridge so it is abovethe design high-water elevation requires lessearth work and material costs, which createssavings—and savings are critical when fundingis restricted.Occasionally we have special projects suchas a 700-ft-long, five-span precast, prestressedconcrete beam bridge across the Des MoinesRiver. This structure was constructed with beamsranging in span length from 130 to 140 ft thatwere specially designed for the project.These unusual projects teach us a great dealabout using materials to their fullest. That,in turn, helps us to design the more standardbridges that we deal with every year.___________________Robert Kieffer is County Engineer, Boone County,Iowa.Accelerated BridgeConstructionNot all of the county’s bridges utilizestandard designs. In 2006, the countyworked with the Bridge EngineeringCenter at Iowa State University in nearbyAmes and the Iowa Department ofTransportation to determine the feasibilityof using precast concrete componentsto accelerate bridge construction.T h r o u g h t h e F e d e r a l H i g h w a yAdministration Innovative BridgeResearch and Construction Program,120th Street Bridge over Squaw Creekwas constructed using several differentprecast, high-performance concreteelements. The result was a 152-ft-long,three-span bridge featuring precastconcrete abutment footings, precast piercaps, and precast full-depth transverselypretensioned and longitudinally posttensioned,8-in.-thick deck panels.Standard 32-in.-deep precast, prestressedconcrete I-beams were used, with four(rather than the standard five) beams perspan. The Mackey Bridge won the awardas Best Owner-Designed Bridge in thePrecast/Prestressed Concrete Institute’sDesign Awards Competition for 2007.Information learned from the projectabout designing completely withprecast concrete elements will benefitfuture projects especially in the areas ofscheduling and staging. We believe thatanother such design would move evenfaster due to the steep learning curve weexperienced.The Mackey Bridge in Boone, Iowa, was designedwith precast concrete components as a feasibilityproject to determine how construction could beaccelerated. Photos: Iowa DOT.Editor’s NoteIf your county has a high percentage ofconcrete bridges or some interesting andinnovative concrete bridges and would like tobe featured in ASPIRE, please let us know atinfo@aspirebridge.org.
National Ready Mixed Concrete AssociationThe National Ready Mixed Concrete Association issponsoring the Third Annual Concrete Technology Forum:Focus on Sustainable Development. The symposium will bringresearchers and practitioners together to discuss the latestadvances, technical knowledge, continuing research, tools,and solutions for concrete and sustainable development.Over 50 technical sessions on state-of-the-art developments,new construction techniques, and product formulations thatoptimize environmental performance of concrete constructionwill be presented including:• Pervious Concrete Systems;• Concrete’s Impact on Urban Heat Islands;• The Carbon Footprint of Concrete;• Sustainable Development Initiatives; and• Optimizing Recycled Content.A product expo featuring companies that offer productsand services for sustainable development will be open duringthe conference. Attendees will earn valuable professionaldevelopment hours (PDHs) and will receive a copy of theconference proceedings.NRMCA, based in Silver Spring, Md., represents theproducers of ready mixed concrete and the companies thatprovide materials, equipment, and support to the industry. Itconducts education, training, promotion, research, engineering,safety, environmental, technological, lobbying, andregulatory programs.National Ready Mixed Concrete Association, 900 SpringStreet, Silver Spring, MD 20910, 888-84NRMCA (846-7622),www.nrmca.org.Bridge MonitoringKnow more about your bridges.At Campbell Scientific, we design rugged, stand-alone dataacquisition systems for any size of bridge. From short-term testingto long-term monitoring, our systems can provide youwith valuable decision-making data.(435) 750-9692www.campbellsci.com/bridgesCAMPBELL ®SCIENTIFIC, INC.WHEN MEASUREMENTS MATTERAspire.indd 12/13/08 9:54:45 AMASPIRE, Spring 2008 | 63
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EDITORIALPhoto: Ted Lacey Photograp
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ASPIRE Spring 08 - Aspire - The Concrete Bridge Magazine

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