In this paper, the authors present a stress wave-based active sensing method to detect the crack in FRP-reinforced concrete beams. The embedded smart aggregates (SAs), which utilize Lead Zirconate Titanate (PZT) as transducers, are employed in this research to generate and sense the stress wave. Three specimens are involved in the experimental program and each is made of concrete, longitudinal distributed reinforcement, steel stirrups, main bar (FRP bar or steel bar), and four SAs. A pair of SAs installed on the lower part of the main bar and the other pair of SAs mounted on the upper part of main bar are utilized to monitor the crack occurrence and development in the three test specimens. The signals received by the SA sensors are analyzed in both time domain and frequency domain. The wavelet packet energy is used to extract damage features. The applied load-vertical displacement curves of mid-span in the specimen are obtained. Experimental results show the test specimens experience crushing failure when the concrete compression exceeds its compressive strength. Increasing the contact area between FRP bar and concrete can effectively improve the cracking load of the FRP-reinforced concrete beam and reduce the cracking speed and depth of FRP-reinforced concrete beam; on the other hand, increasing the elastic modulus of the main bar can slow down the crack development of concrete on the upper side of the main bar and decrease the displacement of reinforced concrete beam during the loading test process. The research results show that the developed piezoceramic-based active sensing method, though low-cost, can monitor the crack-induced damage and estimate the process of damage degree in real-time, and has potentials to provide an early warning of crack occurrence and development for FRP-reinforced concrete beams.

Cracks in oil and gas pipelines cause leakage which results in property damage, environmental pollution, and even personal injury or loss of lives. In this paper, an active-sensing approach was conducted to identify the crack damage in pipeline structure using a stress wave propagation approach with piezoceramic transducers. A pipeline segment instrumented with five distributed piezoceramic transducers was used as the testing specimen in this research. Four cracks were artificially cut on the specimen, and each crack had six damage cases corresponding to different crack depths. In this way, cracks at different locations with different damage degrees were simulated. In each damage case, one piezoceramic transducer was used as an actuator to generate a stress wave to propagate along the pipeline specimen, and the other piezoceramic transducers were used as sensors to detect the wave responses. To quantitatively evaluate the crack damage status, a wavelet packet-based damage index matrix was developed. Experimental results show that the proposed method can evaluate the crack severity and estimate the crack location in the pipeline structure based on the proposed damage index matrix. The sensitivity of the proposed method decreases with increasing distance between the crack and the mounted piezoceramic transducers.

This paper presents the development of an electric, self-heating concrete system that uses embedded carbon nanofiber paper as electric resistance heating elements. The proposed system utilizes the conductive properties of carbon fiber materials to heat a surface overlay of concrete with various admixtures to improve the concrete's thermal conductivity. The development and laboratory scale testing of the system were conducted for the various compositions of concrete containing, separately, carbon fiber, fly ash, and steel shavings as admixtures. The heating performances of these concrete mixtures with the carbon fiber heating element were experimentally obtained in a subfreezing ambient environment in order to explore the use of such a system for deicing of concrete roadways. Analysis of electric power consumption, heating rate, and obtainable concrete surface temperatures under typical power loads was performed to evaluate the viability of a large scale implementation of the proposed heating system for roadway deicing applications. A cost analysis is presented to provide a comparison with traditional deicing methods, such as salting, and other integrated concrete heating systems. Christiana Chang et al 2009 Smart Mater. Struct. 18 127001 Smart Materials and Structures Systems from nanoto macroscale

Piezoceramic-based active sensing is a useful approach to structural health monitoring. This approach often involves a large number of distributed piezoceramic transducers. It may be confusing to incorporate each sensor data. It is desired to develop an automated health monitoring approach to obtain a comprehensive and accurate health monitoring result by simultaneously interpreting data from all sensors. In this paper, an innovative data fusion enabled structural health monitoring (SHM) approach based on the Dempster-Shafer (D-S) evidence theory is proposed to obtain comprehensive SHM results for a distributed sensor network in a civil infrastructure. Considering that evidence from multiple different information sources (sensor data) has different levels of significance, not all evidence is equivalently effective for the final decision. A weighted fusion damage index (WFDI) is proposed to perform damage identification based on the authors’ recently developed piezoceramic-based smart aggregates. Experimental data of a two-story concrete frame was used to study the effectiveness of the proposed weighted fusion damage index. Analyses show that the proposed weighted fusion damage index can reveal the damage status of different areas of the frame. The results are consistent with the visual inspection of the cracks on the concrete frame.

This work presents an adaptive robust sliding-mode control scheme based on Lyapunov's direct method for active vibration control of a flexible beam using PZT (lead zirconate titanate) sensor and actuator. PZT, a type of smart materials, has the advantages of high reliability, high bandwidth and solid state actuation and is adopted here in forms of surface-bond PZT patches for vibration control. Two adaptive robust sliding-mode controllers for vibration suppression are designed: one uses a discontinuous bang-bang robust compensator and the other uses a smooth compensator with a hyperbolic tangent function. Both controllers guarantee asymptotic stability as proved by the Lyapunov's direct method. Experimental results showed that both controllers suppress vibrations of the flexible beam with the PZT sensor and actuator. However, the bang-bang robust compensator causes small-magnitude chattering because of the discontinuous switching actions. With the smooth compensator, vibration is quickly suppressed and no chattering is induced. Furthermore, the robustness of the controllers is successfully demonstrated by adding mass to the flexible beam.

Bolted structures are commonly used in civil infrastructure. It is important to perform bolt inspection regularly to ensure the safety of structures. Traditional bolt inspection methods are time-consuming; moreover, bulky instruments are needed in these methods. In this paper, a piezoceramic based active sensing approach is developed to perform the health monitoring of bolted structures. Surface-bonded piezoceramic patches are used as health monitoring transducers. Wavelet packet analysis is used to analyze the sensor data to extract the features that indicate bolt looseness. Based on wavelet packet analysis results, a damage index is developed to quantitatively evaluate the damage status. To verify the effectiveness of the proposed method, a bolted connection experiment with piezoceramic transducers was performed. In the experiment, the looseness of the bolt is adjusted by a torque wrench. Experimental results show that the proposed approach is effective to detect and evaluate bolt looseness.

This paper presents a proof-of-concept experimental study of an innovative active-sensing approach for damage detection of concrete piles by using embedded piezoceramic transducers. In the proposed active-sensing approach, one piezoceramic transducer is used as an actuator to generate a stress wave to propagate through the concrete pile and the other distributed piezoceramic transducers are used as sensors to detect the wave response. Cracks or damage inside the concrete structure act 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 or damage. Experiments were performed on two bored piles instrumented with embedded piezoceramic transducers. The experimental results demonstrate the effectiveness of the proposed approach for pile damage detection.

In this paper, a piezoceramic-based wireless sensor network (WSN) was developed for health monitoring of wind turbine blades with active sensing approach. The WSN system has an access point that coordinates the network and connects to a PC to control the wireless nodes. One wireless node functions as an actuator to excite an embedded piezoceramic patch with desired guided waves. The remaining wireless nodes function as sensors to detect and transmit the wave responses at distributed locations. The damage status inside the blade was evaluated through the analysis of the sensor signals. Based on wavelet packet analysis results, a damage index and a damage matrix were developed to evaluate the damage status at different locations. To verify the effectiveness of the proposed approach, a static loading test and a wind tunnel test were performed in the Laboratory of Joint Wind Tunnel and Wave Flume at Harbin Institute of Technology (HIT), China. Experimental results show that damage in wind turbine blades can be detected and evaluated by the proposed approach.

Concrete-Filled Steel Tube (CFST) has been widely adopted in high-rise buildings and bridges as a typical structural member carrying vertical loads in recent years. The debonding between the steel tube and the concrete can dramatically reduce the confinement effect of steel tube on the concrete and decrease the load-carrying capacity and the ductility of the CFST. It is still challenging to develop reliable debonding monitoring and detection techniques for CFST because of the inaccessibility of the interface. In this study, an active interface condition monitoring approach for CFST by the use of lead zirconate titanate (PZT) piezoceramics based functional smart aggregates (SAs) embedded in concrete as actuator and PZT patches bonded on the surface of the steel tube as sensors is proposed and verified experimentally. Laboratory tests are performed on the CFST column, in which the deboning is mimicked by setting four thin styrofoam plates with different sizes on different locations of the four internal surfaces of the steel tube, respectively, before casting the concrete. The responses of the PZT sensors are measured when each SA is excited with sweep sinusoidal signals. According to the Fourier spectra and two evaluation indices based on the wavelet packet analysis on the PZT sensors measurements, the artificially mimicked debonding areas are detected successfully. Analysis on the sensitivity of the two evaluation indices shows that the indices based on wavelet packet analysis are more sensitive to the debonding defect. The proposed PZT based active debonding monitoring method provides an innovative approach to detect the debonding damage of CFST columns.

In this study, multifunctional carbon nanofiber (CNF) paper-based nanocomposite coating was developed for wind turbine blades. The importance of vibration damping in relation to structural stability, dynamic response, position control, and durability of wind turbine blades cannot be underestimated. The vibration damping properties of the nanocomposite blades were significantly improved and the damping ratio of the nanocomposite increased by 300% compared to the baseline composite. In addition, the CNF paper-based composite exhibited good impact-friction resistance, with a wear rate as low as 1.78×10−4mm3/Nm. The nanocomposite also shows the potential to improve the blockage of water from entering the nanocomposite, being a superhydrophobic material, with a contact angle higher than 160.0°, which could improve the longevity of a wind turbine blade. Overall, multifunctional nanocomposite coating material shows great promise for usage with wind turbine blades, owing to its excellent damping properties, great friction resistance, and superhydrophobicity.

Structural health monitoring of concrete structures under seismic loads has always attracted a lot of attention in the earthquake engineering community. In this paper, two tests of structural health monitoring of concrete columns using piezoceramic-based sensors are presented. The first test was a shake table test of a reinforced concrete (RC) column. A piezoceramic-based device, called a 'smart aggregate', was pre-embedded and adopted for the structural health monitoring of the concrete column under earthquake excitations. The second test of this study was the in situ health monitoring of RC piers of Niu-Dou Bridge in Taiwan, under seismic loading. RC piers instrumented with the post-embedded piezoceramic-based sensors were tested using reversed cyclic loading. During the shake table test and the in situ reversed cyclic loading test, one sensor was used as an actuator to generate propagating waves, and the other sensors were used to detect the waves. By analyzing the wave response, the existence of cracks can be detected and the severity can be estimated. The experimental results demonstrate the sensitivity and the effectiveness of the piezoceramic-based approach in the structural health monitoring of large-scale concrete structures under earthquake loading.

Structural health monitoring is an important aspect of the maintenance of large civil infrastructures, especially for bridge columns in areas of high seismic activity. In this project, recently developed innovative piezoceramic-based sensors were utilized to perform the health monitoring of a shear-critical reinforced concrete (RC) bridge column subjected to reversed cyclic loading. After the column failed, it was wrapped with fiber reinforced polymer (FRP) sheets, commonly used to retrofit seismically damaged structures. The FRP-strengthened column was retested under the same reversed cyclic loading pattern. Innovative piezoceramic-based sensors, called 'smart aggregates', were utilized as transducers for health monitoring purposes. On the basis of the smart aggregates developed, an active-sensing approach and an impact-hammer-based approach were used to evaluate the health status of the RC column during the loading procedure. Wave transmission energy is attenuated by the existence of cracks during the loading procedure, and this attenuation phenomenon alters the curve of the transfer function between the actuator and sensor. To detect the damage occurrence and evaluate the damage severity, transfer function curves were compared with those obtained during the period of healthy status. A transfer-function-based damage index matrix was developed to demonstrate the damage severity at different locations. Experimental results verified the effectiveness of the smart aggregates in health monitoring of the FRP-strengthened column as well as the unstrengthened column. The experimental results show that the proposed smart-aggregate-based approach can successfully detect damage occurrence and evaluate its severity.

In this paper, the damping characteristics of nanocomposite plates were studied via experimental methods. The nanocomposite plates with different weight percentages of carbon nano fibers (CNFs) in the polymer matrix were fabricated using the vacuum-assisted resin transfer molding (VARTM) process. The damping ratios of the nanocomposite plates were tested and the results show a significant increase of the damping ratio of the plates with a small amount of CNFs. Between a CNF-free plate and a 1.5 wt% CNF-modified plate, over a two-fold decrease in amplitude in the vibration response was observed. The damping factors obtained from dynamic mechanical analysis (DMA) are consistent with the results obtained using PZT. The CNF-modified polymer composites have potential applications in aerospace and wind turbine, where increased structural damping is preferred.

In this paper, a kind of functional smart aggregate (SA) which is based on PZT is employed to detect the predesigned delamination damage in a CFST column specimen. Three SAs are embedded into the concrete of a CFST column specimen as actuators and a number of PZTs are bonded on designed locations of the outside surface of the CFST specimen as sensors. Laboratory tests are performed on the CFST column, in which the delamination is mimicked by bonding four thin Styrofoam plates with different sizes on different areas of the four internal surfaces of the steel tube, respectively, before casting concrete. The responses of all the employed PZT sensors are measured when one of the SAs is excited with swept sine signals. Based on the defined damage index based on the wavelet analysis on the PZT sensors measurements, the artificially mimicked delamination areas are detected successfully and the defined damage index is sensitive enough to the delamination damage in the CFST specimen.

Structural health monitoring is an important issue for the maintenance of large-scale civil infrastructure, especially for bridge columns. In this paper, an innovative piezoceramic-based approach is developed for the structural health monitoring of reinforced concrete columns. An innovative piezoceramic-based device, smart aggregate, is utilized as a transducer for health monitoring purposes. To investigate the seismic behavior of RC bridge columns, structural health monitoring tests were performed on two bridge columns under combined reversed cyclic loading at Missouri University of Science and Technology. Experimental results show that the proposed smart aggregate-based approach successfully evaluated the health status of concrete columns during the loading procedure.

In structural health monitoring, damage detection results have uncertainty due to the measurement noise, modeling error and environment changes. In this paper, data fusion based on the Dempster-Shafer (D-S) evidence theory was employed to decrease the uncertainty level and improve the accuracy of damage identification. A weighted fusion damage index (WFDI) was proposed to perform damage identification. A two-story concrete frame was fabricated as the object for the structural health monitoring test. Experimental results have verified the effectiveness of the proposed method, which will improve damage identification accuracy and increase the reliability of damage identification.

It is important to detect damage before catastrophic failure occurs in wind turbine blades. In this paper, a piezoceramic-based wireless sensor network (WSN) system was developed for health monitoring of wind turbine blades. Using embedded distributed piezoceramic patches, an active-sensing wireless sensor network was developed. The WSN system has an access point that coordinates the network and connects to a PC to control the wireless nodes. One wireless node functions as an actuator to excite an embedded piezoceramic patch with desired guided waves. The remaining wireless nodes function as sensors to detect and transmit the wave responses at distributed locations. The damage status inside the blade was evaluated through the analysis of the sensor signals. Based on wavelet packet analysis results, a damage index and a damage matrix were developed to evaluate the damage status at different locations. To verify the effectiveness of the proposed approach, a static loading test and a wind tunnel test were performed in the Laboratory of Joint Wind Tunnel and Wave Flume at Harbin Institute of Technology (HIT), China. Experimental results show that damage in wind turbine blades can be detected and evaluated by the proposed approach.

The concept of smart aggregates, a distributed intelligent multi-purpose sensor network (DIMSN) for civil structures, has been developed to address three important issues including early-age concrete strength monitoring, impact detection and evaluation, and structural health monitoring. This paper mainly discusses employing smart aggregates' active sensing property to form feedback in the DIMSN to reduce damage-location detecting times for fast time-response and low power-cost. This is an optimal decision-making subject and we present concept of the Geometry Structure matching method (GSM) with the Expert System theory (ES) to build the decision-making module. The designed controller is evaluated on a 2-story concrete frame model instrumented with the DIMSN as a testing object by means of MATLAB simulations. Simulation results show that the proposed method has performed successfully in selecting an actuator in the DIMSN for detecting damage location.

Structural health monitoring is an important issue for the maintenance of large-scale civil infrastructures, especially for bridge columns. In this paper, an innovative piezoceramic-based approach is developed for the structural health monitoring of reinforced concrete columns. An innovative piezoceramic-based device, the smart aggregate, is utilized as a transducer for the purpose of health monitoring. To investigate the seismic behavior of reinforced concrete (RC) bridge columns, structural health monitoring tests were performed on two bridge columns under combined reversed cyclic loading at the Missouri University of Science and Technology. The proposed smart aggregate based approach successfully evaluated the health status of concrete columns during the loading procedure. Sensor energy plots and 3D normalized sensor energy plots demonstrated that the damage inside attenuated the transmitted energy. The wavelet packet based damage index and sensor history damage index evaluate the damage development in concrete columns under cyclic loading.

Shape memory alloys (SMAs) are a relatively new class of functional materials, exhibiting unique thermo-mechanical behaviors, such as shape memory effect and superelasticity, which enable their great potentials in seismic engineering as energy dissipation devices. This paper presents a study of the thermomechanical behaviors of superelastic SMAs wire, specially emphasizing on the influence of strain rate. Cyclic tensile tests on superelastic NiTi SMA wires under quasi-static and dynamic loadings were carried out to assess their dynamic behaviors. An internal temperature variable which indicates the influence of loading rate under various strain amplitudes was introduced to the Liang's constitutive equation of SMA. Numerical simulation results based on the proposed constitutive equations and experimental results are in good agreement. The findings in this paper will assist the future design of superelatic SMA-based energy dissipation devices for seismic protection of structures.