I-240 MemFix4

When the Tennessee Department of Transportation (TDOT) faced the urgent need to replace or repair four deficient structures over I-240 in Memphis, subjecting roadway users to another long-term construction project simply wasn’t an option. With traffic levels of approximately 180,000 vehicles per day, TDOT wanted this critical project completed quickly, with minimal impact to travelers.

The four bridges in the project, dubbed MemFix4, are two new Poplar Interchange bridges; a new Norfolk Southern Railroad (NSR) bridge; and rehabilitation of the concrete Park Avenue bridge. This $54 million project was delivered under the CM/GC delivery method—the second-ever CM/GC transportation project in the state of Tennessee. TDOT, Benesch, and Kiewit worked together in the design phase to develop innovative ideas to address the numerous site challenges and project needs while maintaining the ability to meet the project’s aggressive schedule.

The WB and EB Poplar Avenue bridge replacements required multiple innovative prefabricated bridge elements. The constructed Poplar Ave. bridges consist of a 263-ft, two-span bridge for WB Poplar and a 222-ft, two-span bridge for EB Poplar. For the replacement of these structures, extensive modeling and structural analysis was required to address high seismic conditions. The team developed several custom elements. These included custom steel bearings and framing, over 13,000 linear ft of micropiles, new substructures constructed under traffic, and modular bridge superstructures—all of which addressed site challenges while completing the project in just 18 months.

The project team used accelerated bridge construction (ABC) methods to address site constraints and the necessity for minimal impacts to traffic. This led to the Poplar Avenue bridges being built off-site at a “bridge farm,” rolled to the site using self-propelled modular transporters (SPMTs), and then lifted into place using large crawler cranes. Once the bridges were constructed, Kiewit was able to complete the planned widening of I-240 to alleviate the lane drop that the entrance ramps required.

Because the existing piers for the Norfolk Southern (NS) Rail Bridge were founded on spread footings, it was not cost-efficient to upgrade the existing bridge’s substructures to meet current seismic design standards. TDOT realized that the next project needed to replace the structures while minimizing impacts to the thousands of vehicular travelers through this interchange and the nearly 20 trains per day on the NS/I-240 overpass.

To replace this bridge, a temporary shoofly structure was constructed just inches away from the existing bridge. It was composed of temporary concrete piers supported by a foundation of over 6,000 linear ft of micropiles. Leaving train traffic largely uninterrupted during construction, the permanent steel superstructure supporting a ballasted track was erected on the shoofly alignment and trains were switched onto this alignment. With trains traveling on the shoofly structure, the old bridge was demolished and the new substructures were built. The two new 1,100-ton superstructure sections were then laterally slid 35 ft into place, one track at a time, during two weekend Interstate closures.

The Memphis area is located in the influence zone of the New Madrid Fault, which in 1811 and 1812 produced four of the most powerful earthquakes east of the Rocky Mountains in recorded history. The team spent significant effort during the design phase to ensure that solutions could be constructable while still meeting the seismic demands. Designers focused on the impacts of time during the construction phase, especially when it came to key elements that would be built during weekend closures. Benesch used finite element modeling to precisely design elements such as the bearing anchors to minimize the materials and labor required while still meeting the design requirements.

For more on the I-240 MemFix4 project, see “A Bridge Replacement in Four Parts” in the October 2019 issue of Modern Steel Construction.

Project Team

• Steel detailer and fabricator: W&W | AFCO Steel, Little Rock, Ark. *AISC MEMBER* *AISC CERTIFIED*

• Additional detailer: CRC Steel Detailing LLC, Fort Worth, Texas

• Steel erector and general contractor: Kiewit Infrastructure Co., Brentwood, Tenn.

• Engineer: Benesch, Nashville, Tenn.

• Owner: Tennessee Department of Transportation, Nashville, Tenn.