Photos

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I photographed this bridge from Tennessee bank during sunset over Arkansas state. It has been named after Hernando DeSoto — the famous Spanish explorer who discovered the Mississippi River in 1541.

With its two flowing main arches and over 2,000 lights, the bridge is an elegant structure on the Memphis skyline. Built in late 1960’s with very little seismic protection and therefore would not be serviceable if a damaging earthquake occurred. Opened in August 1973, it carries interstate 40 over the Mississippi River between Arkansas and Tennessee. The bridge sits over the southeast edge of the New Madrid Seismic zone. The New Madrid Fault System running 120 miles from Illinois to Arkansas is considered to be the highest earthquake risk in the United States outside of the West Coast while the bridge was originally designed for only wind forces; earthquake loads were not considered.

Recognizing the potential danger, it became a high priority of the highway authorities to provide a seismic retrofit on this structure. The 30-year-old bridge has just been undergoing retrofitting to withstand the next big earthquake in Mid-America. The bridge had $170 million worth of the latest designs of earthquake reinforcement in this earthquake-prone area. With the new bearing design installed, this will allow the bridge deck to slide with an earthquake for about 22 inches in any direction, riding out the shock waves. The University of Memphis has installed a seismic instrumentation system of 114 sensors at 38 locations on the main channel spans to monitor the performance of the Hernando DeSoto Bridge during an earthquake. This bridge is the first existing long-span bridge in the New Madrid Seismic Zone to be instrumented for seismic monitoring.

Upon completion, it has a total of 3.3 miles long and contains 164 spans, 160 piers, and 10 abutments. The main spans over the channel consist of two tied arch truss spans and five steel box girder spans. The approaches and connecting ramps to the West consist of pre-stressed concrete I beams and steel plate girders. To the East, the approaches and connecting ramps consist entirely of steel plate girders. The original expansion joints allowed only limited longitudinal movement, and no transverse movement. This beautiful tribute to bridge building skill is listed in the Guiness Book of World Records as being the largest free standing letter of the alphabet in the world.



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