Seismic Vulnerability of the Highway System

Task F2-1: Design and Implementation of Seismic Instrumentation for the
Cape Girardeau Cable-Stayed Bridge
Subject Area: Special Studies

Principal Investigator(s) and Institution(s)
Mehmet Çelebi, U.S. Geological Survey
Nicholas P. Jones, Consultant

The acquisition of structural response data during earthquakes is essential to confirm and develop methodologies for analysis, design, repair and retrofitting of earthquake resistant structural systems. Particularly for urban environments in seismically active regions, acquisition of response data from structures including lifelines such as bridges, by using seismic instrumentation, is one of the basic requirements for a thorough investigation of the effects of earthquakes on the structures. In order to understand the structural responses thoroughly, it is necessary to record ground motions at the free-field in the vicinity of the structures, in addition to structural arrays which should include sensors for soil-structure interaction (SSI) effects. The New Madrid area, the location of the 1811 - 1812 New Madrid earthquakes, is a seismically active region requiring earthquake hazard mitigation programs including those related to investigation of strong shaking of structures and the potential for ground failures in the vicinity of structures.

The objective of this task is to develop a detailed and executable scheme for seismic instrumentation of the Cape Girardeau cable-stayed bridge across the Mississippi River between Missouri and Illinois, which is currently under construction. The instrumentation will be deployed on and in the vicinity of the new bridge.

Early planning of seismic instrumentation schemes is a necessity in order to cover installation of basic hardware during the construction phases (such as conduits and cables to interconnect the sensors to recorders and conduits for deployment of downhole accelerometers). In addition to other objectives which may require special purpose instruments and hardware, for seismic engineering studies, three other objectives are sought. In planning for the overall scheme, it is important to clearly identify these objectives:

1. Instrumentation of the superstructure and pier foundations.
2. Instrumentation of the free-field in the vicinity of the structure including those related to downhole measurements and horizontal spatial arrays to assess the differential motions at the piers of the long span structure.
3. Ground failure arrays in the vicinity of the structure.

The scope of this task is limited to detailing the seismic instrumentation covering the first two objectives only. In developing the instrumentation scheme, geotechnical considerations related to the bridge will be taken into account. It is important to note also that the proposed instrumentation is for strong-motion recording and not for low-amplitude weak motions. For low-amplitude weak motions, which are outside the scope of this task, special purpose temporary deployment schemes should be adopted.

The actual acquisition of hardware for instrumentation will be done via funding allocated under related project Task F2-2.

Through this task, the USGS will:

Prepare the instrumentation design (scheme and detailed plans for implementation). In carrying out this subtask, only state-of-the-art hardware will be considered;

Develop the itemized list of hardware;

Solicit vendor quotations in accordance with purchase procedures set by the FHWA project contract officer and MCEER project manager; and provide technical consulting support to the Missouri Department of Transportation (MoDOT) during the installation of the system. It is assumed that MoDOT will be responsible for the actual hardware installation/construction.

USGS, as part of its earthquake hazard reduction program, in addition to carrying out the above tasks in designing and deployment of instrumentation, will also establish a mechanism and appropriate agreements with MoDOT and the FHWA to maintain the instruments, retrieve, process, and disseminate strong-motion response data following events in the future.

In addition, a consultant (Dr. Jones) will be employed to conduct an independent review and check of the final instrumentation design prepared under item 1 above.

Anticipated Start Date and Duration
January 1, 1999 - 24 months