Interpreting measurement data to extract meaningful information for damage detection is a challenge for continuous monitoring of structures. This paper presents an evaluation of two model-free data interpretation methods that have previously been identified to be attractive for applications in structural engineering: moving principal component analysis (MPCA) and robust regression analysis (RRA). The effects of three factors are evaluated: (a) sensor-damage location, (b) traffic loading intensity and (c) damage level, using two criteria: damage detectability and the time to damage detection. In addition, the effects of these three factors are studied for the first time in situations with and without removing seasonal variations through use of a moving average filter and an ideal low-pass filter. For this purpose, a parametric study is performed using a numerical model of a railway truss bridge. Results show that MPCA has higher damage detectability than RRA. On the other hand, RRA detects damages faster than MPCA. Seasonal variation removal reduces the time to damage detection of MPCA in some cases while the benefits are consistently modest for RRA.Keywords: Moving principal component analysis; robust regression analysis; damage detection; damage detectability; time to damage detection; seasonal temperature variation.Evaluating two model-free data interpretation methods for measurements that are influenced by temperature
IntroductionRecently, the collapse of civil structures such as the I-35W bridge (USA, 2007) [1-2] and the Paris Airport (France, 2004) [3] has decreased public confidence in the safety of structures.Thus, to ensure that structures behave according to design criteria, it is useful to monitor their performance. Monitoring for possible damage is referred to as structural health monitoring (SHM). Due to advances in sensor technology, data acquisition systems and computational power, the number of structures that are monitored is growing. Thus, large quantities of measurement data are retrieved every day and much more will be available in the future.Extracting useful information from this data to detect damage is a challenge for SHM. This task is even more difficult when measurement data are influenced by environmental variations, such as temperature, wind and humidity. Brownjohn et al [4] studied the thermal effects on performance on Tamar Bridge and showed that thermal effects dominate the measured bridge behaviour. Catbas et al. [5] observed that the peak-to-peak strain differential due to temperature over a one-year period is more than ten times higher than the strain due to observed maximum daily traffic.Generally, there are two classes of data interpretation methods in SHM: model-based methods and model-free methods. These two classes are complementary since they are appropriate in different contexts. Strengths and weaknesses of both classes have been summarized in the ASCE state-of-the-art report on structural identification of constructed systems [6].Model-based data interpretation...