Structural Health Monitoring of Fiber Reinforced and FRP Strengthened Concrete Elements under Axial Compression using Piezoelectric based Smart Aggregates

Jain, Saumitra (2017) Structural Health Monitoring of Fiber Reinforced and FRP Strengthened Concrete Elements under Axial Compression using Piezoelectric based Smart Aggregates. Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

The Thesis is divided into three parts. First part of thesis discuss about monitoring of concrete cylinders with and without steel fibers using smart aggregates. P iezoceramic smart aggregates are used to monitor the failure mechanism of concrete under pure compression and efficiency of various column strengthening techniques . The smart sensor is prepared by embedding a water - proof piezoceramic transducer (PZT) patch with wire leads into a smart aggregate. Smart aggregates are embedded at the desired locations in the concrete member before casting. An active sensing approach is employed in this study to ana lyze the damage behavior of concrete under compression. A pair of smart aggregates including one as an actuator to convert the excitation signal into compression wave while the other to act as a sensor for sensing the wave signals. Wavelet packet analysis is used to analyze the recorded signals. Cracking pattern changes at different levels of loading, thereby modifying the signal characteristics. A damage index is formulated on the basis of wavelet packet analysis. A total of six cylinders with and without steel fiber reinforcement and twelve RC columns were cast and tested to failure under compression. Compression tests on steel fiber reinforced concrete cylinders (SFRC) showed that the improvement in ductility and better post peak behavior under compressio n was due to addition of steel fibers. Second part of thesis discuss about efficiency of different strengthening techniques using PZT smart aggregates. RC columns were strengthened using different strength techniques and the efficiency of these techniques were studied with the help of PZT based smart aggregates. The experimental results show that the proposed method of using PZT smart aggregates and damage index based on wavelet analysis is effective in identifying the damage progression in concrete members . Among all column strengthening techniques, Hybrid technique (i.e. combination of Near Surface Mounted (NSM) and externally bounded (EB) Fiber Reinforced Polymer) seemed to be most effective in hindering damage progression inside concrete columns. In the last part of thesis, an experimentally investigation is carried to study the emergency repair of severely damaged RC columns. In total Six RC columns were cast and all of them were initially damaged by applying axial compression up to 20% decay after achi eving peak load. These columns were repaired by three different techniques which includes (1) Repairing the column by quickset high strength cementitious grout (2) NSM strengthening technique & (3) Hybrid strengthening using combination of NSM CFRP laminat es and CFRP confinement. The efficiency of given techniques were evaluated by three different indices namely strength index, stiffness index and ductility index. Among all the strengthening techniques, Hybrid strengthening technique was found to be most ef ficient in restoring strength, stiffness and ductility lost due to initial damage mechansm.

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