Seismic Instrumentation of Bill E. Emerson Memorial Bridge
Computer rendering of the cable-stayed
Bill E. Emerson Memorial Bridge.
The Bill E. Emerson Memorial Bridge, currently under construction, is a signature, cable-stayed bridge that crosses the Mississippi River near Cape Girardeau, Missouri. Jointly owned by the Illinois and Missouri DOTs, the bridge is located in the New Madrid Seismic Zone, thus necessitating the implementation of seismic hazard mitigation measures.
The Federal Highway Administration (FHWA) initiated the seismic instrumentation project in October of 1996. A group comprised of FHWA, MoDOT, HNTB Corp. (the bridge designer and construction manager for the project), MCEER, US Geological Survey (USGS), and others developed a plan for the seismic instrumentation of the bridge.
MCEER is charged with designing and acquiring the seismic instrumentation network under its Highway Project research program. The bridge is scheduled to be completed by March 2003.
MCEER has employed the USGS to complete the design, finalize the hardware acquisition and prepare a bid package for the hardware. Independent consultants and academia have been providing technical review of the constantly evolving instrumentation plan. It includes instruments to record free-field motions at the surface and downhole locations. It is designed to capture the overall motion of the cable-stayed bridge, including translational, torsional, rocking and translational soil-structure interactions at the foundation levels. The instrumentation scheme will also provide insight into the horizontal and vertical spatial variation of recorded ground motions.
Photo courtesy of Rick Lamb and Ron Robertson, MoDOT
View of the bridge from the Illinois approach spans.
Currently, two alternative strategies for the instrumentation system are under consideration. The first option involves a conventional scheme and includes on-site recording capabilities without real-time data transmission. However, constantly developing technology in the field now allows adaptation of a wireless instrumentation scheme and real-time data transmission of the recorded data. Thus, coupled with the former, the second alternative provides for continuous recording of data via a Central Recording System (CRS). Accordingly, data acquisition blocks will be equipped with wireless routers which then establish communication with the CRS to stream data out using standard internet communication protocols. Overall, once deployed, the instrumentation scheme will provide extensive strong-motion response recording capability to facilitate different types of studies and to assess the performance of the bridge during strong-motion events.
Data obtained from the instrumentation will help designers and researchers better understand the behavior and performance of large, cable-supported bridges under both weak and strong ground motion, and improve their ability to design more resilient structures in the future. The data will also assist the bridge owners in maintaining and inspecting the structure following a moderate to large earthquake, thus helping to ensure public safety.
Submitted by Gokhan Pekcan,University of Nevada, Reno