Numerical Simulation of Single-Point Mount PZT-Interface for Admittance-Based Anchor Force Monitoring

This study investigates the dynamic characteristics of a smart PZT interface mounted on a prestressed anchorage to verify the numerical feasibility of the admittance-based anchor force monitoring technique. Firstly, the admittance-based anchor force monitoring technique through a single-mount PZT interface is outlined. The admittance response of the PZT interface-anchorage system is theoretically derived to show the proof-of-concept of the technique for anchor force monitoring. Secondly, a finite element model corresponding to a well-established experimental model in the literature is constructed. The effect of anchor force is equivalently treated by the contact stiffness and damping parameters at the bottom surface of the anchorage. Thirdly, the admittance and the impedance responses are numerically analyzed and compared with the experimental data to evaluate the accuracy of the numerical modelling technique. Fourthly, the local dynamics of the PZT interface are analyzed by modal analysis to determine vibration modes that are sensitive to the change in the contact stiffness (i.e., representing the anchor force). Finally, the admittance responses corresponding to the sensitive vibration modes are numerically analyzed under the change in the contact stiffness. The frequency shift and the admittance change are quantified by statistical damage indices to verify the numerical feasibility of the anchor force monitoring technique via the smart PZT interface. The study is expected to provide a reference numerical model for the design of the single-point mount PZT interface.

Anchor Force Monitoring Using Impedance Technique with Single-Point Mount Lead-Zirconate-Titanate Interface: A Feasibility Study

As a key load-bearing element in a prestressed structure, the anchor should be appropriately monitored to secure its as-built prestressing force. In previous studies, the impedance-based prestress force monitoring technique through a mountable lead–Zirconate–Titanate (PZT) interface was developed. However, the previous design of the PZT interface uses a two-point mount technique through two bonding layers, causing inconveniences during installation and replacement processes. To address this issue, we propose an alternative PZT interface model for prestress force monitoring based on the impedance method. The proposed model uses a single-point mounting technique that allows it to be more conveniently installed and replaced on a host structure. First, the electromechanical impedance of the proposed PZT interface is theoretically derived. The proof-of-concept of the proposed PZT interface for impedance monitoring is then shown by finite element modelling. Afterwards, a lab-scaled experiment is conducted on an anchoring system to demonstrate the practical application feasibility of the proposed technique. The obtained results show that the proposed technique can produce impedance responses that are highly sensitive to the prestress force. The performance of the proposed model for impedance-based prestress force monitoring is found to be comparable with the previous techniques (the washer-type mount and the two-point mount). Due to its advantage of simple design, the newly designed PZT interface is promising for the future development of the impedance-based anchor force monitoring systems in practice.

A Technic for Ground Anchor Force Determination from Distributied Strain Using Fiber Optic OFDR Sensor with the Rejection of a Temperature Effect

Anchor systems are widely used to stabilize soil slope and suppress slope failure. Thus, monitoring conditions of an anchor system is important to prevent disasters due to slope failure. The slope condition can be indirectly monitored by sensing the tensile force applied to the anchor because the slope deformation directly affects the anchor force. Previously, we propose a way to monitor the tensile force of the anchor by measuring the strain field on a bearing plate using a distributed fiber optic sensor (OFDR) and experimentally demonstrate that the anchor force has a large correlation with the strain distribution on the bearing plate. However, it was found that a spatial variation of the strain and thermal strain due to temperature change makes it difficult to get a reliable correlation coefficient. In this study, we newly propose a way to get a reliable correlation coefficient between the anchor force and the strain field on the bearing plate. We install a distributed optical fiber sensor in two concentric circles on the bearing plate and measure circumferential strain distribution. We take average values of the strain field in each circle as representative strain values minimizing the spatial variation and takes a difference of the two strains to exclude the temperature effect. We experimentally demonstrate that the proposed method gives a reliable correlation coefficient between the anchor force and the strain field on the bearing plate. This technique can be applied to various anchor systems to monitor the anchor force and manage the anchor systems safely.

Calculation of Slope Stability Anchoring Force by Using Inclined Slice Method

Generally, the slope stability anchoring force is calculated by using vertical slice methods. A more feasible algebraic expression for the calculation of slope stability anchoring force is presented herein, which is obtained from the force limit equilibrium conditions of inclined slices based on the concept of the inclined slice method. The examples described herein show that the results from the calculation of the anchor force by using this method are similar to those by using conventional methods such as Swedish slice method and simplified Bishop method if the slope stability and safety factor are given. In addition, calculation of the anchoring force is simplified by using this method with accurate results, making it significantly easy for engineers and technicians to familiarize with and apply.