For reinforced concrete structures, the use of fiber-reinforced polymer rebars to replace the steel reinforcement is a topic that is receiving increasing attention, especially where corrosion is a serious issue. However, fiber-reinforced polymer rebar–reinforced concrete always carries the risk of structural failure initiated from the debonding damage that might occur at the reinforcement–concrete interface. This study employed an electro-mechanical impedance–based structural health monitoring technique by applying lead–zirconate–titanate ceramic patches to detect the debonding damage of a carbon fiber–reinforced polymer rebar reinforced concrete. In the experimental study, a carbon fiber–reinforced polymer rebar reinforced concrete specimen was fabricated and it was subjected to a pullout test to initiate the debonding damage at the reinforcement–concrete interface. The impedance and admittance signatures were measured from an impedance analyzer according to the different debonding conditions between the reinforcement and the concrete. Statistical damage metrics, root-mean-square deviation and mean absolute percentage deviation, were used to quantify the changes in impedance signatures measured at the lead–zirconate–titanate patches due to debonding conditions. The results illustrated the capability of the electro-mechanical impedance–based structural health monitoring technique for detecting the debonding damage of fiber-reinforced polymer rebar–reinforced concrete structures.

Interlayer slide is a common type of damages in geological and civil engineering. Interlayer slide damage is an internal cause of landslide and collapse, which may further result in catastrophic losses. It is desirable to develop a real-time monitoring system that is able to detect this kind of damage. In this paper, an experimental feasibility study on interlayer slide detection using piezoceramic smart aggregates based on the active sensing approach was performed. A mortar specimen, sandwiched with a weak interlayer, was fabricated before conducting the loading test. Two pairs of smart aggregates were installed at specific positions inside of the formwork before pouring the mortar. With the embedded piezoceramic patch transducers, the smart aggregates possess both the actuation and sensing functions. Two smart aggregates were employed as actuators, which generated the stress wave to propagate through the weak interlayer. The other two smart aggregates were used as sensors to receive the wave responses. In addition, a wavelet packet analysis was applied to develop a damage index to assess the initiation and development of the interlayer slide. Experimental results show that the proposed method was able to detect the interlayer slide damage.

Due to the loss of preload, structural failure caused by bolt loosening is common in engineering structures. Effective monitoring of bolted connections is of great importance in providing early warning to the structural maintenance department. In this study, a novel and reusable electromechanical impedance (EMI) instrumented wearable piezoelectric ring (WPR) was proposed to detect bolted connection loosening. In the experimental investigation, the EMI spectra of three identical WPRs during the bolt-loosening process were acquired and analyzed. It was concluded that bolt looseness changes can be qualitatively and quantitatively characterized by conductance spectra. Specifically, the resonance frequency and amplitude at certain frequencies were reduced correspondingly as bolts loosen. This was further validated by finite element model simulation results. Moreover, two statistical metrics including mean absolute percentage deviation (MAPD) and root mean square deviation (RMSD) were adopted to evaluate different degrees of bolted connections quantitatively. Both metrics showed an increasing tendency during the bolt loosening process in three different frequency bands. It was found that both metrics demonstrated a significant linear correlation with bolt torque variations. Both of them serve as reliable indicators to detect loose bolts in the bolted connection. The present work verifies the feasibility and applicability of using EMI-instrumented WPR to monitor bolted connections.

Interlayer slide damage is one of the main causes of landslide hazard, inflicting huge economic losses and casualties. It is urgent to accurately detect the initiation and development of the interlayer slide damage in real time. In this paper, a study on the feasibility of using the electro-mechanical impedance (EMI) technique to detect the interlayer slide damage was presented. The main purpose of this paper is to investigate the application of the EMI technique for interlayer slide detection using piezoceramic smart aggregates (SAs). In the experimental study, three small landslide specimens with a weak interlayer in the middle were fabricated. For each specimen, three piezoceramic SAs were post-embedded at specific positions, which were located above the weak interlayer inside the structure. The specimens were subjected to a compressive test to initiate an interlayer slide along the weak layer. The whole loading process was monitored with a precision impedance analyzer by measuring the admittance (reciprocal of impedance) of the SAs over time. The statistic metrics, including root mean square deviation (RMSD) and mean absolute percentage deviation (MAPD), were introduced to quantify the variations in admittance signatures due to interlayer slide damage. It was found that the admittance signatures and statistic metrics were sensitive to the interlayer slide damage. The experimental results verify the feasibility and practicality of using EMI technique to detect the interlayer slide.

Compaction is a crucial process in road construction and the compactness is an important parameter in determining the road foundation quality. Traditional compaction monitoring methods are based on different principles. The major principle of these techniques is detecting the water content and bulk density of the soil, and then calculating the dry density and the compactness. The disadvantages are laborious, low accuracy, low efficiency and costly for large scale measurement. These drawbacks may limit their application in certain aspects. In this paper, a novel electromechanical impedance (EMI) based compactness measuring sheet (CMS) for soil compactness monitoring was proposed. The proposed CMS was fabricated by attaching a circular piezoceramic patch onto a circular sheet with a larger size. Eight round CMSs with a diameter of 150 mm, 100 mm, 80 mm, 50 mm were fabricated in this experimental study. Among them, four CMSs were embedded into soil and subjected to compression tests to simulate the increased soil compaction. In this study, the conductance signatures of the proposed CMS were collected and analyzed during the increasing soil compaction process. Experimental results demonstrated that all the peak magnitudes in the conductance signatures in the selected frequency range of 160 kHz to 310 kHz were reduced with the increase of soil compaction. It showed that some specific frequencies shifted to the right side during the compaction process. The variations in the conductance signatures were then quantified with the aid of three statistical metrics. These metrics include root mean square deviation (RMSD), mean absolute percentage deviation (MAPD), and correlation coefficient deviation (CCD). Through calculation, all these metrics increase with the increase of soil compaction, which can be employed as indicators in the soil compaction process. To obtain more insight into CMS electromechanical system, the finite element analysis were also performed to study the EMI response. The simulation results well verified the experimental results. This preliminary study has verified that the proposed EMI based CMS is feasible and effective in monitoring soil compactness and shows a promising application prospect.

The 2016 Ecuador M 7.8 earthquake ruptured the subduction zone boundary between the Nazca plate and the South America plate. This M 7.8 earthquake may have promoted failure in the surrounding crust, where six M ≥ 6 aftershocks occurred following this mainshock. These crustal ruptures were triggered by the high coulomb stress changes produced by the M 7.8 mainshock. Here, we investigate whether the six M ≥ 6 aftershocks are consistent with the positive coulomb stress region due to the mainshock. To explore the correlation between the mainshock and the aftershocks, we adopt a recently published high-quality finite fault model and focal mechanisms to study the coulomb stress triggers during the M 7.8 earthquake sequence. We compute the coulomb failure stress changes (ΔCFS) on both of the focal mechanism nodal planes. We compare the ΔCFS imparted by the M 7.8 mainshock on the subsequent aftershocks with the epicenter location of each aftershock. In addition, the shear stress, normal stress, and coulomb stress changes in the focal sources of each aftershock are also computed. Coulomb stress changes in the focal source for the six M ≥ 6 aftershocks are in the range of −2.17–7.564 bar. Only one computational result for the M 6.9 aftershock is negative; other results are positive. We found that the vast majority of the six M ≥ 6 aftershocks occurred in positive coulomb stress areas triggered by the M 7.8 mainshock. Our results suggest that the coulomb stress changes contributed to the development of the Ecuador M 7.8 earthquake sequence.