Evaluating Fatigue Damage Using Strain Data

The US and many other countries around the world face the challenge of an aging infrastructure. In the US, there are 600,000 bridges in its inventory and a significant percentage of those bridges are nearing the end of their intended design life. Labor-intensive, visual inspections are used to identify possible safety problems in bridges and determine which ones can be safely kept in-service. This paper outlines ongoing research to improve inspection practices by providing the technology and methodology for real-time monitoring of steel bridges. A 76-year old, fracture-critical bridge was monitored with strain gages to determine the number and size of stress cycles in fatigue-sensitive members. From the cycle count, Palmgren-Miner’s rule can be used to determine an effective stress. The remaining fatigue life can then be calculated and compared to existing conditions and the age of the bridge. Because damage is expected to escalate over time, more frequent inspections may be needed when a bridge approaches its fatigue life. Thus, determining the remaining fatigue life of a bridge can be useful to bridge owners in prioritizing inspections. This paper will present the fatigue evaluation of the bridge and discuss the effectiveness of the recently-installed retrofit.

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