We present a statistical process control framework to support structural health monitoring
of transportation infrastructure. We contribute an integrated, generally-applicable (to various
types of structural response data) statistical approach that links the literatures on statistical
performance modeling and on structural health monitoring. The framework
consists of two parts: The first, estimation of statistical models to explain, predict, and control
for common-cause variation in the data, i.e., changes, including serial dependence, that
can be attributed to usual operating conditions. The ensuing standardized innovation series
are analyzed in the second part of the framework, which consists of using Shewhart and
Memory Control Charts to detect special-cause or unusual events.
We apply the framework to analyze strain and displacement data from the monitoring
system on the Hurley Bridge (Wisconsin Structure B-26-7). Data were collected from April
1, 2010 to June 29, 2011. Our analysis reveals that, after controlling for seasonal effects, linear
trends are significant components of the response measurements. Persistent displacement
may be an indication of deterioration of the bridge supports. Trends in the strain data
may indicate changes in the material properties, i.e., fatigue, sensor calibration, or traffic
loading. The results also show that autocorrelation and conditional heteroscedasticity
are significant sources of common-cause variation. Use of the control charts detected 43
possible special-cause events, with approximately 50% displaying persisting effects, and
25% lasting longer than one week. Analysis of traffic data shows that unusually heavy loading
is a possible cause of the longest special-cause event, which lasted 11 days.
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