## 3 Health Monitoring and Test Results  
The structural health monitoring test is based on the use of some PPTs as actuators to generate propagation stress waves and others as sensors to receive the waves. The amplitude of propagation waves is attenuated by the presence of cracks and damage inside the concrete wall structure, causing the transmitted energy of the propagation waves to decline as their amplitude decreases. Therefore, the drop in propagation wave amplitude or transmission energy between the healthy and damaged states of the structure is related to the severity of the cracks or damage inside it. The transmission energy that is received by the sensor is given by  
\[E=\int_{t_{i}}^{t_{f}}v^{2}\,dt \tag{1}\]  
where \(t_{i}\) and \(t_{f}\) are the times for starting and end of the measurement, respectively, \(v\) express the filtered piezoelectric signal that passed the band-pass filter with a bandwidth from 0.98\(f_{c}\) to 1.02\(f_{c}\) Hz, where \(f_{c}\) is the excitation frequency of the actuator. \(E_{h}\) is the transmission energy of the sensor when the structure is healthy and is evaluated using Equation (1). \(E_{i}\) is the transmission energy of the damaged RC wall structure after the test run \(i\). The energy-based damage index (D.I.) of the RC wall structure after the test run \(i\) is given by  
\[D.I.=\frac{\left|E_{h}-E_{i}\right|}{E_{h}} \tag{2}\]  
Figure 6: Configuration of the post-embedded transducers. Figure 7: Locations of the actuators and sensors in the specimen and the wave path. This damage index yields the damage status to the structure based on the transmission energy difference between the healthy and damaged states. A damage index close to zero expresses that the RC wall is in a healthy state or has only negligible damage. A damage index of close to unity means that the structure is very seriously damaged. This work applied the cyclic horizontal loads on the top beam of the specimens using the displacement control, as shown in Figure 8. For the specimen of RCW1 at the drift ratio of 0.25%, the slight cracks developed horizontally at the bottom end of the boundary columns. Additionally, the cracks with an inclination angle close to 45 degrees distributed uniformly in the region of the wall panel. At the drift ratio of 0.5%, the crack development is similar to the drift of 0.25%. However, the foundation and bottom end of the boundary columns have slight spalling of concrete cover since their compressive strength of concrete is relatively lower than the wall panel. Figure 9 shows the cracking patterns at each drift level and the final failure status of the specimen at the drift ratio of 1.0% and the concrete at the bottom end of the boundary columns and foundation crushed in the second cycle. The experimental results showed which the foundation of the existing RC frame is much weaker than the retrofitted RC wall. Then, the failure could be found at the interface of the foundation of the existing RC frame and the retrofitted RC wall. The major cracks could be found on the positions of the foundation of the existing RC frame under the boundary columns. Due to the specimen was failed in bending behavior, the middle part of the interface of the foundation of the existing RC frame and the retrofitted RC wall was not found with too many cracks. For the specimen of RCW2 at the drift ratio of 0.25%, the crack development is similar with RCW1. When the drift ratio reached 0.5%, the extended cracks with the width of 1 mm at the interface between the RC wall panel and top beam are observed. Figure 10 shows the cracking patterns at each drift level and the final failure status of the specimen. The failure mode of RCW2 occurs at the drift ratio of 1.0% in which the concrete at the top end of the boundary columns and at the wall top corner crushed in the second cycle. This experimental results showed that the strength of the interface of existing RC frame and the retrofitted RC wall is not strong enough to transfer the shear force.