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Bridge Fatigue Life Indicating System

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Final rept.

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The Twin Coupon FLI system which is suitable for use on mobile Army bridges has been developed, enhanced, and field tested in this program. The device utilizes two precracked aluminum coupons attached directly to the bridge. By measuring the crack lengths in the coupons, and knowing the initial crack lengths, the stress and cycles applied to the bridge can be directly calculated. A previous program conducted extensive laboratory tests to define the crack growth rates and develop a computer program to calculate the loading history. This program demonstrated the system in field crossing tests of the Armored Vehicle Launched Bridge AVLB at Aberdeen Proving Grounds. Several system enhancements were concurrently developed in the laboratory. Numerous tests demonstrated a bonded attachment method for the coupons which eliminates the bridge damage which could result from the original bolted attachment method. Several remote crack measurement systems were evaluated and an accurate method, which would permit complete sealing of the coupons, was demonstrated. The potential for reduction of the coupon size was also shown in the laboratory. This report presents field data and correlations from the vehicle crossing tests on the AVLB during the period of January to April 1991 a total of four two- coupon sets were applied to the two AVLBS for 2,000 crossing tests at Aberdeen Proving Grounds. The test results provided adequate proof of the Twin Coupon Concept.

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  • Civil Engineering

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