Structural Health Monitoring Using Smart Sensors - ideals ...

1
1
Normalized accumulated stress
measurement 3 measurement 2 measurement 1
0.5
0.3
0
1
0.5
0.3
0
1
0.5
0.3
Normalized accumulated stress
measurement 3 measurement 2 measurement 1
0.5
0.3
0
1
0.5
0.3
0
1
0.5
0.3
0
3 4 5 6 7 8 9 1011 7 8 9 10 111213 1415 1112 1314 151617 1819
Element ID
(a)
3 4 5 6 7 8 9 1011 7 8 9 10 111213 1415 1112 1314 151617 1819
Figure 8.14. Damage detection (damaged element: Element 9): (a) mass perturbation
DLV; and (b) SDLV.
0
Element ID
(b)
1
1
Normalized accumulated stress
measurement 3 measurement 2 measurement 1
0.5
0.3
0
1
0.5
0.3
0
1
0.5
0.3
Normalized accumulated stress
measurement 3 measurement 2 measurement 1
0.5
0.3
0
1
0.5
0.3
0
1
0.5
0.3
0
3 4 5 6 7 8 9 1011 7 8 9 10 111213 1415 1112 1314 151617 1819
Element ID
(a)
0
3 4 5 6 7 8 9 1011 7 8 9 101112131415 111213141516171819
Element ID
(b)
Figure 8.15. Damage detection (damaged element: Element 10): (a) mass perturbation
DLV; and (b) SDLV.
From a theoretical perspective, false-negatives, on the other hand, are not expected if
conditions such as linearity of the structure and no observation noise are satisfied. No
false-negative damage detection is found in Bernal (2002) and Gao (2005). In the Imote2
experiments, false-negatives are observed. For example, Figure 8.16 (a) shows the
damage detection results when element 11 is replaced with the damaged element. Seven
false-negative damage detection cases are observed in this figure. The SHM system
cannot detect damage in this case, even though the three sensor communities commonly
monitor the replaced element. Gao (2005) stated that detecting damage in the vertical and
diagonal elements located close to the midspan of the truss structure was found to be more
difficult than for other elements. Damage detection of elements carrying small force under
self-weight is considered challenging. Small forces in vertical element 11 under self-
151