Monitoring Instrumentation of I35W Bridge

Principal Investigator(s):

Cathy French, Professor, Civil, Environmental and Geo-Engineering


  • Carol Shield, Former Professor, Civil, Environmental and Geo-Engineering
  • Henryk Stolarski, Professor, Civil, Environmental and Geo-Engineering

Project summary:

The new I-35W Bridge was instrumented incorporating "smart bridge technology" by Figg Engineering Group in conjunction with Flatiron-Manson. The purpose of the instrumentation is to monitor the structure during service and to use this information to investigate the design and performance of the bridge. Instrumentation includes static sensors (vibrating wire strain gages, resistive strain gages, and thermistors in the foundation, bridge piers, and superstructure, as well as fiber optic sensors and string potentiometers in the superstructure) and dynamic sensors (accelerometers in the superstructure). Finite element models were constructed, taking into account measured material properties, to further explore the behavior of the bridge. The bridge was tested using static and dynamic truck load tests, which were used, along with continually collected ambient data under changing environmental conditions, to validate the finite element models. These models were applied to gain a better understanding of the structural behavior, and to evaluate the design assumptions presented in the Load Rating Manual for the structure. It was found that the models accurately recreated the response from the instrumented bridge, and that the bridge behaved as expected during the monitoring period. Findings from the research are presented in a report documenting the bridge instrumentation scheme, material testing, finite element model construction methodology, the methodology and results of the truck tests, validation of the models with respect to gravity loads and thermal effects, measured and modeled dynamic modal characteristics of the structure, and documentation of the investigated assumptions from the Load Rating Manual.

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