Concrete piles are widely used in the construction of civil infrastructures and it is important to perform the health
monitoring of concrete piles for safety purposes. In this paper, a piezoceramic-based innovative approach is proposed for
the damage detection and health monitoring of concrete piles. A multi-functional piezoceramic-based transducer device,
the smart aggregate, is developed for health monitoring purposes. An active-sensing network is formed by embedding
the proposed smart aggregates at the pre-determined locations in the concrete piles before casting. In the proposed
approach, one smart aggregate is used as an actuator to excite the desired waves and the other distributed smart
aggregates are used as sensors to detect the wave responses. An energy distribution vector is formed based on the
wavelet-packet analysis results of sensor signals. A damage index is formed by comparing the difference between the
energy distribution vectors of the health concrete pile and that of the damaged concrete pile. To verify the effectiveness
of the proposed approach, two concrete piles instrumented with smart aggregates are used as testing objects. One
concrete pile is intact and the other has a man-made crack in the middle of the pile. Experimental results show that the
there are differences between the energy distribution vectors of the damaged pile and that of the intact pile due to the existence of the crack. The proposed method has the potential to be applied to perform automated integrity inspections for new piles and for the long-term health monitoring of piles in services.
Past RC panel tests performed at the University of Houston show that reinforced concrete membrane elements under reversed cyclic loading have much greater ductility when steel bars are provided in the direction of principal tensile stress. In order to improve the ductility of low-rise shear walls under earthquake loading, high seismic performance shear walls have been proposed to have steel bars in the same direction as the tensile principal direction of applied stresses in the critical region of shear walls. This paper presents the results of reversed cyclic tests on three low-rise shear walls with SMA bars. The height, width, and thickness of the designed shear walls are 1.0 m, 2.0 m, and 0.12 m, respectively. SMA bars are provided in the directions of 27 degrees to the horizontal that are in the diagonal direction. The reinforcing bars of the shear walls are in vertical and horizontal directions. The ratios of both SMA and reinforcing bars are 0.24%. The main parameter used in the study is the type of SMA bar, namely Superelastic and Martensite SMA bars. The test results from the walls with SMA bars are also compared to a conventional wall without SMA bars. Test results also show that the maximum shear strengths of the tested walls are affected by the SMA bars. It was found that the shear wall with Martensite SMA bars has greater residual displacement. In contrast, the shear wall with superelastic SMA bars has less residual displacement. At the ultimate state, one of the four superelastic SMA bars buckled, resulting in less energy dissipation capacity than the expected value. Preventing buckling of SMA bars is the research focus in the near future.
It is important to conduct early age strength monitoring of concrete structures because it will help speed up construction.
Piezoelectric-based strength monitoring method provides an innovative experimental approach to conduct concrete
strength monitoring at early ages. In the presented paper, piezoelectric transducers were embedded into the concrete
specimen during casting. The development of strength of concrete structures was monitored by observing the
development of harmonic amplitude from the embedded piezoelectric sensor at early ages. From the experimental
results, the amplitude of the harmonic response decreased with the increment of the concrete strength. The amplitude of
the harmonic response from piezoelectric sensor dropped rapidly for the first week and continued to drop slowly as
hydration proceeded which matches the development of the concrete strength at early ages. Concrete is heterogeneous
and anisotropic which makes it difficult to be mathematically analyzed. Fuzzy logic has the advantage to conduct
analysis without requiring a mathematical model. In this paper, a fuzzy logic system was trained to correlate the
harmonic amplitude with the concrete strength based on the experimental data. The concrete strength estimated by the
trained fuzzy correlation system matches the experimental strength data. The proposed piezoelectric-based monitoring
method has the potential to be applied to strength monitoring of concrete structures at early ages.