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A Passive Fatigue Life Indicator for Highway Bridges
Author(s) and Affiliation(s):
Douglas Thomson and Gopal Samavedam Foster Miller, Inc., Waltham, MA William Wright, Turner-Fairbank Highway Research Center Federal Highway Administration, McLean, VA
Principal Investigator:
Douglas Thomson
Federal Highway Administration
Research Start Date:
September 21, 1995
Expected Completion Date:
February 1, 1997
Research Objectives:
The primary objective of this study is to develop and demonstrate a low cost, unpowered system for tracking the fatigue loading of highway bridges. This system will serve as a useful tool for bridge owners in the assessment of fatigue and the optimal deployment of inspection and maintenance resources. The twin coupon fatigue life indicator (TCFLI) system works on the principle that stable propagation of an existing "precrack" in a coupon can be directly related to the applied load and number of cycles. The innovation of this system is in the use of two coupons of different metals which are attached directly to the structure and thus experience the same loading histogram. By simply measuring the crack lengths in the coupons at the beginning and end of any period, the average load level and number of cycles during that period is determined since the cracks will propagate at different rates in the two metals.
Expected Products or Deliverables:
The result of this project will be a prototype TCFLI system which is ready for deployment in large scale field demonstration tests. The TCFLI will be a low cost (< $200) passive device which can provide bridge loading history information. Simple to deploy and cost effective, the TCFLI can be mounted on all bridges within an owner's inventory to provide relative usage information between similar bridges and to track changes in the traffic patterns for a particular bridge.

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