r - The Hong Kong Polytechnic University

Figure 15 Impact location on FRP wrapped RC column
During the health monitoring test, an impact hammer was used to generate stress waves, and smart
aggregates were used as sensors to detect the wave responses. The impact hammer was used to
repeatedly strike the column on marked location I and location II, as shown in Figure 15. The
health monitoring results for impact tests on location I are shown in Figures 16, 17 and 18. From
the damage index matrix based on the frequency response magnitude ranging from 2k-10k Hz, as
shown in Figure 16, the damage index increased slightly at Test Number 3 and continues to
progressively increase during the course of the test. This indicates slight increased internal damage
during the test. The damage index increased greatly in Test Number 17, when the FRP ruptured,
indicating major structural damage in the column. This shows that the column loses its
confinement as a result of FRP rupturing, and that the existing cracks inside the column open up
substantially at this stage.
Figure 17 show the damage index matrix based on the frequency response magnitude ranging from
10k-20k Hz, while Figure 18 show the damage index matrix based on the frequency response
magnitude ranging from 18k-20k Hz. While comparing the damage index matrices based on
frequency response among different frequency ranges, as shown in Figures 16, 17 and 18, it can
clearly be observed that damage index matrix based on a higher frequency range is more sensitive
in detecting the damage. The development trend of the damage index matrix based on the higher
frequency range (10 k-20 kHz) in Figure 17 is more sensitive and smoother than that in Figure 16.
This smooth development trend is more apparent in Figure 18, where the frequency range used to
calculate the damage index matrix ranges from 18 to 20 kHz. Figure 19 shows the damage index
matrix for FRP wrapped RC column when the column was impacted on location II. The frequency
range used to calculate the damage index matrix was from 18 to 20 KHz. From the damage index
matrix, it can be seen that at test 17, there is a tremendous increase in damage index values, which
indicates major structural damage in the column. The health monitoring results from impact
location II is consistent with the results from impact location I. Figure 20 and Figure 21 show the
weighted damage index for the FRP wrapped RC column when the column was impacted on
location I and II, respectively. From the weighted damage index for both cases, it can be seen that
the damage index increases tremendously at test 17, which reveals that the overall damage status
of the FRP wrapped RC column failed at test 17.
Damage index
1
0.5
0
1 2 3 4 5 6
Sensor No.
5
Test No.
Figure 16 Damage index matrix based on
frequency response magnitude among
2k-10kHz (struck on location I)
10
15
Damage index
1
0.5
0
1 2 3 4 5 6
Sensor No.
5
Test No.
Figure 17 Damage index matrix based on
frequency response magnitude among 10k-20kHz
(struck on location I)
10
15
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