The I-40 Mississippi River Bridge, crossing from Arkansas into Memphis, Tennessee, represents a vital highway link in the United States for commerce, defense and transportation. Located on the southeast edge of the New Madrid Seismic zone, considered to be the highest earthquake risk zone in the U.S. apart from the West Coast, the bridge was originally built in the 1960’s with little seismic protection. Considering the potential for another earthquake and closure of the two bridge crossings in the Memphis area due to earthquake damage, the Tennessee Department of Transportation (TDOT) and Arkansas State Highway and Transportation Department (AHTD) gave priority status for retrofitting the I-40 bridge and its approaches.
TRC was awarded its first design contract in 1992 by TDOT to develop the seismic retrofit strategies and preliminary cost estimates for serviceability and no-collapse criteria, as well as develop the seismic design criteria. Serviceable performance for this “lifeline” structure was selected using a 2500-year return period for the seismic hazard loading. Since then, TRC has developed the plans, specifications and estimates (PS&E) packages for $270 million worth of construction. The design has been in performed accordance with the AASHTO LFD design specifications and the most recent AASHTO LRFD Seismic Design Guidelines (Second Edition) which TRC developed. Over this period, numerous bridge structure types have been analyzed and designed for seismic retrofit for the Arkansas approaches, the main channel spans (steel tied arch) and Tennessee approaches and ramps. A structure replacement bridge on the Arkansas approach, approximately ½-mile in length, was designed by TRC in 2005.
Overall, this project has set new standards in seismic design in the United States. With recent advances in technology, isolation became a viable option for the bridge to reduce construction costs. Friction pendulum bearings were utilized for the isolation bearings on the main channel spans, while lead-core rubber bearings were utilized on several approach spans. In addition, modular swivel expansion joints were utilized to accommodate maximum seismic movements of 48 inches.
TRC was subsequently selected by TDOT in 2000 to provide Construction Management (CM) services for the retrofit work and we have worked on all nine phases of construction since which will be completed in August 2015. TDOT has provided overall administration oversight on the design and CM contracts, while AHTD has provided design oversight on the I-40 approach structures located in Arkansas.
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