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/295658
A C C E L E R AT E D B R I D G E C O N S T R U C T I O N Improving safety and reducing congestion in the construction zone were two primary factors that motivated the Iowa Department of Transportation (Iowa DOT) to develop a policy for accelerated bridge construction (ABC). Although several ABC projects had been completed in Iowa prior to the policy implementation in 2012, the ABC policy allowed for a systematic approach to selecting ABC projects. As part of the ABC policy implementation, the Iowa DOT selected bridge sites across the state for the purpose of demonstrating various ABC methods and developing workforce expertise. The Massena Bridge site was identified for a lateral slide. One of the advantages of this method is the use of traditional construction methods. Massena Design Constructed in 1930, the original bridge over a small stream in Cass County near Massena, Iowa, had been designated as structurally deficient with a sufficiency rating of 38, load posted for one truck at a time, and was in need of major rehabilitation or replacement. A 120-ft-long by 44-ft-wide prestressed concrete, single-span structure was chosen to replace the existing 40-ft-long by 30-ft-wide steel beam bridge. With a focus on building internal ABC design expertise, the preliminary and final designs were performed by Iowa DOT engineers. But because this was the first design for a lateral slide in Iowa, a design firm with significant experience in lateral slide was retained to conduct a design-constructability review. The bridge superstructure consists of six 45-in.-deep, prestressed concrete bulb-tee beams with specified concrete compressive strength of 9.0 ksi at 28 days and an 8-in.- thick, cast-in-place concrete deck. While much of a lateral bridge slide design depends on the means and methods chosen by the contractor, the design team chose to show one feasible slide concept and associated details in the plans. Components for the slide that were anticipated to be permanently incorporated into the final structure included the slide shoe, jacking pockets, bearing pads, and solid end diaphragms. The solid end diaphragm details were different than those in a traditional design. The end diaphragm had to accommodate jacking pockets, high-strength threaded rods, and anchorages used to push or pull the bridge superstructure. Laboratory Confirmation For design of the sliding shoe and bearing pads, the coefficient of friction was needed for the interaction between the pad and specified stainless steel. The Iowa DOT commissioned laboratory testing by Iowa State University (ISU) of a full-scale mock-up of the slide shoe and bearing pads. The tests were performed in both lubricated and non- lubricated conditions with the lubricant being common dish washing soap. Test results indicated that the suggested 10% coefficient of friction for design was reasonable. Iowa DOT had previous ABC experience and research results with precast concrete abutment footings founded on driven HP10 piling. However, an HP14x117 was selected to meet the design and constructability requirements of this project. Extrapolating the original research data to a pile about twice as large was not felt to be appropriate and so ISU was commissioned to do laboratory testing of the new precast concrete abutment footing to pile pocket detail. The laboratory testing confirmed the design capacity of the new by Ahmad Abu-Hawash and James Nelson, Iowa Department of Transportation MASSENA BRIDGE This photo shows the finished Massena Bridge after the lateral slide replacement. All photos: Iowa Department of Transportation. L AT E R A L S L I D E R E P L AC E M E N T ASPIRE, Spring 2014 | 33 AspireBook_Spr14.indb 33 3/21/14 2:21 PM