Optical Phase-Based Method for Dynamic Deflection Measurement of Railroad Bridge

The development of highly reliable structural health monitoring techniques with low-cost is essential to ensure the safety of various aging infrastructures. To measure accurate deflection over the entire structure, in this study, the sampling moire method is applied to two-dimensional displacement measurement of an old and long metal bridge by utilizing repeated pattern marker. The deflection measured from our method corresponded well with that measured from conventional contact-type ring displacement sensor. In addition, we can measure the deflection of the railroad bridge successfully by use of the repeated rivet patterns without any marker. The digital images of natural repeated patterns are analyzed through the sampling moire method and the deformation is evaluated. This moire technique features comparable accuracy to conventional one despite low-cost and easy setup. The aged deterioration of bridges can be diagnosed with deflection measurement at regular intervals. The developed measuring technique is expected to be widely applied to the inspection of various large-scale structures for infrastructure triage.