This paper summarizes the authors' recent pioneering research work in piezoceramic-based smart aggregates and their innovative applications in concrete civil structures. The basic operating principle of smart aggregates is first introduced. The proposed smart aggregate is formed by embedding a waterproof piezoelectric patch with lead wires into a small concrete block. The proposed smart aggregates are multi-functional and can perform three major tasks: early-age concrete strength monitoring, impact detection and structural health monitoring. The proposed smart aggregates are embedded into the desired location before the casting of the concrete structure. The concrete strength development is monitored by observing the high frequency harmonic wave response of the smart aggregate. Impact on the concrete structure is detected by observing the open-circuit voltage of the piezoceramic patch in the smart aggregate. For structural health monitoring purposes, a smart aggregate-based active sensing system is designed for the concrete structure. Wavelet packet analysis is used as a signal-processing tool to analyze the sensor signal. A damage index based on the wavelet packet analysis is used to determine the structural health status. To better describe the time-history and location information of damage, two types of damage index matrices are proposed: a sensor-history damage index matrix and an actuator–sensor damage index matrix. To demonstrate the multi-functionality of the proposed smart aggregates, different types of concrete structures have been used as test objects, including concrete bridge bent-caps, concrete cylinders and a concrete frame. Experimental results have verified the effectiveness and the multi-functionality of the proposed smart aggregates. The multi-functional smart aggregates have the potential to be applied to the comprehensive monitoring of concrete structures from their earliest stages and throughout their lifetime.

https://iopscience.iop.org/article/10.1088/0964-1726/17/3/033001/pdf

Smart aggregates: multi-functional sensors for concrete structures—a tutorial and a review

Applied Hydraulic Transients

Active interface debonding detection of a concrete-filled steel tube with piezoelectric technologies using wavelet packet analysis

Structural health monitoring is an important aspect of maintenance for bridge columns in areas of high seismic activity. In this project, recently developed piezoceramic-based transducers, known as smart aggregates (SA), were utilized to perform structural health monitoring of a reinforced concrete (RC) bridge column subjected to pseudo-dynamic loading. The SA-based approach has been previously verified for static and dynamic loading but never for pseudo-dynamic loading. Based on the developed SAs, an active-sensing approach was developed to perform real-time health status evaluation of the RC column during the loading procedure. The existence of cracks attenuated the stress wave transmission energy during the loading procedure and reduced the amplitudes of the signal received by SA sensors. To detect the crack evolution and evaluate the damage severity, a wavelet packet-based structural damage index was developed. Experimental results verified the effectiveness of the SAs in structural health monitoring of the RC column under pseudo-dynamic loading. In addition to monitoring the general severity of the damage, the local structural damage indices show potential to report the cyclic crack open-close phenomenon subjected to the pseudo-dynamic loading.

Cyclic Crack Monitoring of a Reinforced Concrete Column under Simulated Pseudo-Dynamic Loading Using Piezoceramic-Based Smart Aggregates

A review of vibration control methods for marine offshore structures

With increasing traffic volume follows an increase in the number of overheight truck collisions with highway bridges. The detection of collision impact and evaluation of the impact level is a critical issue in the maintenance of a concrete bridge. In this paper, an overheight collision detection and evaluation system is developed for concrete bridge girders using piezoelectric transducers. An electric circuit is designed to detect the impact and to activate a digital camera to take photos of the offending truck. Impact tests and a health monitoring test were conducted on a model concrete bridge girder by using three piezoelectric transducers embedded before casting. From the experimental data of the impact test, it can be seen that there is a linear relation between the output of sensor energy and the impact energy. The health monitoring results show that the proposed damage index indicates the level of damage inside the model concrete bridge girder. The proposed overheight truck–bridge collision detection and evaluation system has the potential to be applied to the safety monitoring of highway bridges.

https://iopscience.iop.org/article/10.1088/0964-1726/16/2/026/pdf

An overheight vehicle–bridge collision monitoring system using piezoelectric transducers

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.

https://iopscience.iop.org/article/10.1088/0964-1726/20/12/125015/pdf

Structural health monitoring of concrete columns subjected to seismic excitations using piezoceramic-based sensors

Structural Health Monitoring of a Concrete Column Subjected to Shake Table Excitations Using Smart Aggregates

Recently, there has been increasing efforts to incorporate vibration damping or energy dissipation mechanisms into civil structures, particularly by using smart materials technologies. Although papers about structural vibration control using smart materials have been published for more than two decades, there has been little research in developing teaching equipment to introduce smart materials to students via in-classroom demonstration or hands-on experiments. In this paper, an innovative and multi-functional smart vibration platform (SVP) has been developed by the Smart Materials and Structures Laboratory at the University of Houston to demonstrate vibration control techniques using multiple smart materials for educational and research purposes. The vibration is generated by a motor with a mass imbalance mounted on top of the frame. Shape memory alloys (SMA) and magneto-rheological (MR) fluid are used to increase the stiffness and damping ratio, respectively, while a piezoceramic sensor (lead zirconate titanate, or PZT) is used as a vibration sensing device. An electrical circuit has been designed to control the platform in computer-control or manual mode through the use of knobs. The former mode allows for an automated demonstration, while the latter requires the user to manually adjust the stiffness and damping ratio of the frame. In addition, the system accepts network connections and can be used in a remote experiment via the internet. This platform has great potential to become an effective tool for teaching vibration control and smart materials technologies to students in civil, mechanical and electrical engineering for both education and research purposes.

http://iopscience.iop.org/article/10.1088/0964-1726/16/4/043/pdf

An innovative and multi-functional smart vibration platform

Piezoceramic based transducers are widely researched and used for structural health monitoring (SHM) systems due
to the piezoceramic material's inherent advantage of dual sensing and actuation. Wireless sensor network (WSN) 
technology benefits from advances made in piezoceramic based structural health monitoring systems, allowing easy
and flexible installation, low system cost, and increased robustness over wired system. However, piezoceramic
wireless SHM systems still faces some drawbacks, one of these is that the piezoceramic based SHM systems require
relatively high computational capabilities to calculate damage information, however, battery powered WSN sensor
nodes have strict power consumption limitation and hence limited computational power. On the other hand,
commonly used centralized processing networks require wireless sensors to transmit all data back to the network
coordinator for analysis. This signal processing procedure can be problematic for piezoceramic based SHM
applications as it is neither energy efficient nor robust. In this paper, we aim to solve these problems with a
distributed wireless sensor network for piezoceramic base structural health monitoring systems. Three important
issues: power system, waking up from sleep impact detection, and local data processing, are addressed to reach
optimized energy efficiency. Instead of sweep sine excitation that was used in the early research, several sine
frequencies were used in sequence to excite the concrete structure. The wireless sensors record the sine excitations
and compute the time domain energy for each sine frequency locally to detect the energy change. By comparing the
data of the damaged concrete frame with the healthy data, we are able to find out the damage information of the
concrete frame. A relative powerful wireless microcontroller was used to carry out the sampling and distributed data
processing in real-time. The distributed wireless network dramatically reduced the data transmission between
wireless sensor and the wireless coordinator, which in turn reduced the power consumption of the overall system.

Claudio Olmi

Papers

An overheight vehicle–bridge collision monitoring system using piezoelectric transducers

Structural health monitoring of concrete columns subjected to seismic excitations using piezoceramic-based sensors

Structural Health Monitoring of a Concrete Column Subjected to Shake Table Excitations Using Smart Aggregates

An innovative and multi-functional smart vibration platform

Energy efficient wireless sensor network for structural health monitoring using distributed embedded piezoelectric transducers