## 1 Introduction
[PERSON] and [PERSON] [26] combined smart aggregates (to support the wave transmission technique) with surface-bonded PZTs (to support the wave propagation technique) to investigate both the local and overall conditions of an RC structure. [PERSON] et al. [27] proposed an Electro-Mechanical Admittance (EMA) procedure for detecting and evaluating damage in a shear critical RC beam using the admittance signatures of embedded SA transducers and externally bonded piezoelectric patches. [PERSON] et al. [28] developed an innovative portable real-time wireless impedance admittance monitoring system for diagnosing damage to shear-critical RC beams. [PERSON] et al. [29] applied the finite element modeling with admittance-based signature data to analyze its accuracy and to evaluate the potential use of this technique to monitor structural damage in real time. [PERSON] et al. [30] experimentally evaluated an innovative portable wireless real-time SHM system for detecting earthquake damage and the structural integrity of RC members in seismically prone regions. More advanced and interesting applications of PZT sensors for SHM and damage detection can be found elsewhere [31, 32, 33, 34, 35, 36]. Most successful applications of SHM using piezoelectric-based transducers have involved flexural-critical columns or frame specimens. However, a few have involved shear-critical walls subjected to the ground motion. Furthermore, most tests in the investigations cited above focused on the monitoring of damage to whole structures rather than the location of damage. Most wave-based health monitoring methods that involve piezoelectric-based transducers require them to be pre-embedded in the structures before casting. Therefore, the transducer and concrete can be assumed to be well-bonded. Studies of the sensitivity and effectiveness of post-embedded piezoceramic-based transducers for the SHM of existing concrete structures are also very important. With respect to retrofitted RC members, the interface failure or cracks between two structural members (one existing and one added) are important and affect the effectiveness of the retrofit. Furthermore, interface failure or cracks cannot be observed during renovation as part of retrofitting work. The main purpose of this work is to develop the post-embedded PZT transducers that can be used to identify interface failure or cracks between two structural members in retrofit construction. This work involves an experiment on the SHM of RC walls using post-embedded transducers. Cyclic loading is used to test two specimens with post-embedded piezoceramic-based transducers. Since the failure of an interface between the post-installed wall and the existing structure occurs, one of the specimens has damage in its foundation and boundary column and the other one has damage in the top ends of columns and wall. Waterproof post-embedded transducers are used as actuators and sensors for SHM and damage detection during the cyclic loading test. For specimens under cyclic loading, the post-embedded transducers are utilized to identify crack development in and the health status of, an interface between existing and retrofitted structural members. During the cyclic loading test, the distributed post-embedded transducers in the concrete structures are used to perform SHM. For this purpose, one of the transducers is used as an actuator to generate stress waves, while the others are used as sensors that receive the stress waves. The propagation energy of the waves is attenuated in the presence of cracks or damage. The decreased in the transmission energy is correlated with the severity of the damage. The locations of cracks or damage and their corresponding severity can be estimated by analyzing the received wave signals. Experimental results indicate the effectiveness of the piezoceramic-based method in SHM based on the location of damage in shear-critical RC structures under seismic loading.