THESIS
2018
xiv, 99 pages : illustrations (some color) ; 30 cm
Abstract
High-accuracy crack growth monitoring is crucial for the health assessment of concrete
structures, and different kinds of crack growth sensors have been developed and applied in in-service
structures. Those sensors can only measure one dimensional displacement while cracks
might propagate in multiple directions. For two-dimensional (2D) crack growth monitoring,
image-based sensor using traditional photogrammetric algorithms such as the normalized cross-correlation
(NCC) have been developed. The image-based sensor requires prior calibration and is
limited to even cracks whose two sides are of the same height. To broaden the scope of application
to uneven cracks, this study developed crack growth sensors using the moiré technique, which is
less sensitive to the height change of tw...[
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High-accuracy crack growth monitoring is crucial for the health assessment of concrete
structures, and different kinds of crack growth sensors have been developed and applied in in-service
structures. Those sensors can only measure one dimensional displacement while cracks
might propagate in multiple directions. For two-dimensional (2D) crack growth monitoring,
image-based sensor using traditional photogrammetric algorithms such as the normalized cross-correlation
(NCC) have been developed. The image-based sensor requires prior calibration and is
limited to even cracks whose two sides are of the same height. To broaden the scope of application
to uneven cracks, this study developed crack growth sensors using the moiré technique, which is
less sensitive to the height change of two sides of cracks.
In the first generation of developed sensor, the digital sampling moiré (DSM) method is
employed due to its simple setup and high accuracy. The DSM method generates moiré fringes
from a single image through digital image processing, and it measures 2D displacements using
the phase difference of moiré fringes between motion. Compared with the previous sensor using
the normalized cross-correlation (NCC) method, this DSM-based crack sensor is of higher
sensitivity, requires no prior calibration, and is more robust to the change of height difference
between two sides of cracks. However, this sensor is incapable to measure cracks’ in-plane
rotation, which can be observed in the bending structures and the corrosion of the reinforcement
concrete. To simultaneously measure the in-plane rotation and 2D translation of cracks, an
enhanced-DSM (EDSM) method was proposed by integrating the 2D rigid transformation
algorithm with the DSM method. This newly developed algorithm was built in the sensor and
applied to do 3-DOF crack monitoring in a three-point bending test and a reinforcement concrete
corrosion test.
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