r - The Hong Kong Polytechnic University

Smart aggregate
(sensor)
Smart aggregate
(sensor)
Smart aggregate
(actuator)
Impact hammer
(a) (b
Figure 4 (a) Diagram of active-sensing system, (b) Diagram of impact response-based health
monitoring system
The energy deviation of the j th sensor at the k th test is defined as:
(1)
The maximum energy deviation value for the j th sensor for all tests is defined as:
Max (j) = , (k=1, 2, …, m ) (2)
An element in a damage index matrix is the normalized energy deviation, which is defined as:
(3)
where k is the test number, j is the sensor number and m is the total number of tests. Based on
experimental data, a three-dimensional damage index matrix plot can be constructed to reveal the
damage evolution.
For a complex structure, it may be confusing and time-consuming to obtain a comprehensive
overall health monitoirng result based on multiple sensors. In this paper, a weighted damage index
is developed to provide a comprehensive quantitative result based on multiple sensors. The
weighted damage index is defined as:
(4)
where w(j) is weight for a damage index value, n is the total number of sensor data sets used,
is the distance from actuator to sensor, k is the test number, and j is the sensor number. As shown
in equation (4), the weight value w(j) is proportional to the reciprocal of a distance between a
sensor- actuator pair, which means that the smaller the distance between an actuator- sensor pair,
the greater the weight value .
TEST PROCEDURE
The tested RC column was subjected to reversed-cyclic loading using the experimental setup
shown in Figure 5. An axial load equal to 10% of the column’s axial capacity was applied using
the jack shown in Figure 5. A reversed cyclic loading protocol, described in Figure 6, was then
applied on the concrete column to load the structure until failure. The failed column can be
observed in Figure 7. During the loading procedure, the proposed piezoceramic-based smart
aggregates were used as transducers to perform health monitoring to evaluate the health status of
the RC column.
After the failure of the column, all the cracked concrete pieces were removed from the structure,
and it was repaired by replacing grouts in spalling locations. Subsequently, the column was
wrapped with FRP sheets as show in Figure 8. Based on material tests, the FRP sheets used in this
study can be specified with a modulus of elasticity equal to 15,000 ksi and an ultimate strength
equal to 13.2 ksi. The FRP fabric thickness was 0.011 in. The column was retested under
reversed-cyclic loading, as seen in Figure 9. In Figures 10 and 11, rupture of FRP in the repaired
column at failure can be observed. The load versus displacement curves for both tests are shown in
Figure 12. It can be seen from Figure 12 that the FRP effectively confined the concrete. The
strengthening provided by the FRP proved to be successful in recovering the strength loss of the
damaged column, although a reduction in stiffness was observed. During the loading procedure,
the piezoceramic-based smart aggregates were used as transducers to perform health monitoring in
order to evaluate the damage status of the column.
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