Hernando de Soto Bridge Inspections

Memphis, Tennessee and West Memphis, Arkansas

National Bridge Inspection Standards mandate inspections for highway bridges every two years. In keeping with this requirement, the Arkansas Department of Transportation (ARDOT) traditionally performs its own bridge inspections within the state, using traditional methods to inspect all primary and secondary structural bridge members.

However, the state’s two-span, tied-arch truss Hernando de Soto Bridge, which carries Interstate 40 over the Mississippi River between West Memphis, Arkansas, and Memphis, Tennessee, proved too difficult to inspect adequately using traditional methods alone, due to the considerable height, unique structural configuration of the trusses and heavy-traffic considerations.

The 160-foot height of the main navigation spans, combined with the arched configuration of the bridge itself, introduced a high level of complexity to the inspection, making many of the bridge’s structural components inaccessible to inspectors using traditional inspection techniques. The rope access climbing approach required extensive training of the rope-climbing experts to help them understand and prepare for the team’s ascent to the top of the bridge and its far reaches.

For several years, ARDOT turned to Michael Baker and our specially trained team of hands-on, rope-climbing inspectors with their motorized ascenders and other specialized climbing equipment to complete the inspections of the above deck portions of the arch truss. Michael Baker is one of a few engineering firms in the country with this technical capability.

Coordination was key to the success of the inspections. The team scheduled the inspections to minimize traffic delays and avoid unnecessary conflicts with ongoing bridge maintenance projects and coordinated with contractors to share lane closures and staging areas.

Since 2013, each year has presented unique challenges requiring innovative solutions.

• 2013: Michael Baker employed rope access technologies to inspect the above deck portion of the arch truss along with aerial lifts.
• 2015: Ongoing bridge maintenance limited the use of lifts on the eastbound side of the bridge. The team employed two power seats, or motorized ascenders, and developed an efficient circuit to inspect up and down cables. The team also collaborated with local EMS to better understand rescue planning preparations and a third-party consultant to establish a foundation for the rope access program.
• 2017: A collaboration between lifts and rope access occurred establishing a baseline control for comparison where lifts were used to inspect the cables’ free lengths and rope access inspectors focused on the upper portions and connections the lifts couldn’t reach.
• 2019: Michael Baker and ARDOT collaborated on a case study to employ unmanned aircraft systems (UAS) technology alongside lifts for a 1:1 comparison for the cable free length inspection in conjunction with rope access inspectors. UAS reduced the personnel-at-risk hours by nearly 50%.
• 2021: ARDOT authorized the use of UAS to scan the free length of the cables, while rope access inspectors focused on the intricate connections and truss members above. This resulted in a major critical finding in the arch tie closing the structure. During the routine and fracture critical inspection in 2021, the team discovered, by chance, a critical fracture in part of the bridge outside of the company’s scope. The inspection team immediately closed the bridge and contacted authorities to assist with the emergency and closure of the Mississippi River. Our team later served as lead engineer for the emergency repair that improved safety and restored the flow of commerce across the Mississippi River. Read more about this emergency repair project.
• 2023: Michael Baker is to perform the above deck routine and non-redundant steel tension members (NSTM) inspection, including additional advance ultrasonic testing of known weld locations similar to the one which caused the 2021 emergency closure.