DAMAGE DETECTION IN CONCRETE UNDER IMPACT LOAD AT VARYING TEMPERATURES USING PIEZOSENSORS

Abstract

Concrete structures subjected to impact loading exhibit a rapid and severe deterioration, leading to substantial losses in both property and human lives. As temperatures rise, the destructive effects of impact loading intensify. To mitigate such damages and losses, the implementation of Structural Health Monitoring (SHM) in concrete structures becomes imperative. Concrete structures need structural health monitoring (SHM) to avoid these damage and loss. Electromechanical impedance (EMI) technique has emerged as a promising SHM technique for monitoring concrete damage. This study monitors the health of the concrete using EMI under different impact loading at varying temperature conditions. For this purpose, an experiment study has been performed on concrete cube specimens in which different piezo configurations (surface bonded, non-bonded, and jacketed) were installed to acquire the raw signature (conductance and susceptance). The initial phase of the experiment involved subjecting a concrete cube to distinct impact and temperature conditions. In the impact-loading aspect, two drop heights, 3 meters and 3.5 meters, were considered. In the temperature-loading effect, three temperature levels of 50 °C, 100 °C, and 150 °C has been examined. Additionally, the study delved into the combined effects of both impact and temperature. In this combined scenario, the concrete specimen was preheated to temperatures of 50 °C, 100 °C, and 150 °C before being subjected to an impact load. The impact was induced by releasing a free-falling iron ball from two different heights, 3 m and 3.5 m, onto the specimen's top surface. To detect damage in concrete, the initial step involved acquiring the baseline conductance signature, which represents the healthy state of the material, from the sensors. Subsequently, this baseline signature was compared with the signature obtained from the damaged state. For a more comprehensive assessment of concrete damage, the raw signature data has been further analyzed using numerical techniques such as RMSD (Root Mean Square Deviation) and MAPD (Mean Absolute Percentage Deviation). In addition, PZT-based equivalent structural parameters, including stiffness, mass, and damping, were extracted from the raw signature data. This extraction allowed for the identification of changes in the mechanical properties of the specimens, enhancing the understanding of various damage conditions in concrete cubes. In addition to assessing the current damage condition, the study included a crucial element, estimating the remaining life of the structure. This estimation has been made possible through the utilization of equivalent-based parameters. These parameters were employed to gain a more comprehensive understanding of the extent of damage and predict how much longer the structure could be expected to serve its intended purpose. This valuable insight aids in making informed ix decisions regarding maintenance, repair, or replacement to ensure the continued safety and functionality of the structure. Furthermore, temperature compensation techniques were explored to mitigate a limited number of false alarms related to damage conditions arising from the PZT heightened temperature sensitivity. Further the study has been also conducted on the structural members, specifically beams, which were subjected to the combined influence of 3 m impact and three different temperature condition of 50 oC, 100 oC and 150 oC. For better assessment of concrete damage in beam the structural parameter has been also calculated same as the concrete cube. Moreover, the research broadened to encompass boundary conditions, where the concrete cube's performance was evaluated under a fixed boundary condition. In this setup, the concrete cube underwent testing with a 3 m impact height at three distinct temperature levels of 50 °C, 100 °C, and 150 °C for jacketed sensors. To validate the experimental findings, finite element analysis has been conducted, aligning the empirical results with analytical outcomes. The experimental results revealed that jacketed sensors proved to be more effective in health assessments for both boundary conditions. On the basis of statistical tools such as RMSD and MAPD value, both are the reliable tools for calculating the incipient and progressive damage in concrete under the effect of impact loading at varying temperature. The extracted equivalent stiffness with increasing impact number clearly indicates damage propagation in concrete sample for different sensor configuration. The stiffness loss increases with the rise in temperature from ambient to 150°C, ranging from 6.87 % for NBPS sensors to 10.42 % for JKTPS sensors. This data illustrates that the stiffness loss escalates by approximately 3 to 4% with the increase in temperature and also showed satisfactory agreement between the experimental and equivalent plot of x and y. The extracted equivalent stiffness with increasing impact number followed a distinct decreasing pattern (stiffness loss up to 15%) that clearly indicates damage propagation in concrete beam and also showed satisfactory agreement between the experimental and equivalent plot of x and y. Notably, in terms of strain values, the analytical results closely aligned with the experimental data.