r - The Hong Kong Polytechnic University

Figure 2 Location of smart aggregates (view from east
side of column )
Figure 3 Location of smart aggregates
SMART AGGREGATE-BASED STRUCTURAL HEALTH MONITORING SYSTEMS
In recent years, the demand for structural health monitoring of large-scale structures has increased
greatly in order to reduce maintenance costs and enhance safety. Traditional health monitoring
methods, such as using x-ray or ultrasonic C-scan technologies, are expensive and sometimes
ineffective for large-scale structures with limited or no accessibility. Fiber optical sensors,
including the Fiber Bragg Grating sensors, are now used for the health monitoring of various RC
structures (Mehrani et al. 2009, Zhang et al. 2006, Ren et al. 2006, Lu and Xie 2006, Chen and
Ansari, 2000). However, fiber optical sensors offer only local measurements, which greatly limit
their applications. Piezoelectric transducers have emerged as a new tool for health monitoring of
large-scale structures due to having advantages including solid-state actuation, low cost, quick
response and availability in different shapes. In general, there are two major categories of the
piezoelectric-based health monitoring approaches for concrete structures: the impedance-based
health monitoring approach (Hey et al. 2006, Naidu and Bhalla 2003, Tseng and Wang, 2004, Soh
et al. 2000, Bhalla and Soh 2004, Park et al. 2006, Zhao and Li, 2006, Raju et al. 1999) and the
vibration-characteristic approach (Okafor et al. 1996, Song et al. 2007 b , Saafi et al. 2001, Miller et
al. 2002, Na et al. 2003).
In this study, a piezoceramic-based vibration-characteristic approach was applied to perform the
structural health monitoring of a RC column under reversed-cyclic loading. The wave response
detected by the proposed piezoceramic-based smart aggregates was used to evaluate the health
status of the concrete structure during the reversed cyclic loading. Two smart aggregate-based
active sensing systems, as shown in Figure 4, were used for the health monitoring of the concrete
column. In System 1, as shown in Figure 4(a), the piezoelectric transducer in one smart aggregate
was used as an actuator to excite the desired guided waves. In System 2, as shown in Figure 4(b),
an impact hammer was used to strike the column on marked locations to generate the stress waves
to propagate through the column. The piezoelectric transducers in the distributed smart aggregates
were used as sensors to detect wave responses. Cracks inside the RC column acted as stress relief
in the wave propagation path. The amplitude of the wave and the transmission energy will
decrease due to the existence of cracks. The value of the transmission energy drop will correlate
with the degree of the damage inside. For System 1, the transfer function is obtained by using the
smart aggregate actuator signals as input and the smart aggregate sensor signals as output. For
System 2, the signal from the embedded force sensor inside the impact hammer is used as the input
signal for the transfer function; the sensor signal detected from the smart aggregate is used as the
output signal for the transfer function.
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