## 3 Experimental Test Set-Up  
In the laboratory, a three-story aluminum building model was constructed and utilized as a test platform (Figure 1). The building model consisted of rectangular tube beam elements and flat bar column elements, with the connections between them provided by bolts. The bottom plate of the three-story building model was mounted horizontally and supported by two 400 cm long, 25 mm wide steel rails. A spring capable of working in the tensile direction was installed on the bottom surface of the table at the ground level of the three-story system and the plate supporting the entire system. The purpose of this spring was to prevent the system from moving away from the shaker. Additionally, an 8 mm diameter gear shaft connected to this spring and a knob were placed at the end to adjust the tension of the spring. This set-up reduced the collision effect between the shaker output shaft and the floor plate, which occurred at different vibration frequencies, and ensured proper shaking of the system. The floor table on the rails and the other parts of the system mounted on it could move horizontally and on a single axis. The floor table and columns were fixed with 4 M6 bolts made of A2 steel to prevent corrosion from moisture. The entire system was made of aluminum, except for the skid on which the floor table sat and the connection equipment. The total length of the system was 750 cm, the width was 350 cm, and the distance between the floors was 17 cm.  
When any of the bolt connections were loosened, and the system was exposed to environmental and operational conditions, both nonlinear signals due to bolt loosening and signals due to noise were obtained from the sensors. These nonlinear signals represent damage. The primary objective of structural health monitoring is to distinguish the effects caused by damage from noisy signals due to environmental factors and use them as a damage index. By loosening the bolt and allowing 0.3 mm of axial movement from the nut's contacted surface, a damage simulation was created. A feeler gauge was used to measure how far the nut moved. Since there were three bolts in total, a total of 2\({}^{3}\) = 8 scenarios could be produced.  
Figure 1: Three views of the building model (adapted from [31]).  
The building model was mounted on foam that could isolate the noise, sub-plates, rails, shafts, trolleys, shaker, and all mechanical connection equipment that made up the system. This foam reduces the transfer of external noise to the system [31].  
Following the construction of the three-story aluminum building model and the establishment of the experimental set-up, the tests were conducted, employing both the three-accelerometer and single-accelerometer configurations. For the three-accelerometer set-up, the sensors were strategically placed on each floor of the building model to capture comprehensive vibration data across different levels. This configuration aimed to provide detailed insights into the structural response to various stimuli and potential damage occurrences. Conversely, in the single-accelerometer configuration, only one accelerometer was utilized, neglecting the typical placement of sensors on each floor. This scenario simulated situations with limited sensor coverage, which are common in practical applications where deploying multiple sensors might not be feasible due to cost or logistical constraints. By subjecting the building model to controlled vibrations and environmental conditions, the response data from both sensor configurations were collected and analyzed to evaluate the effectiveness of the CNN approach in detecting structural damage under varying sensor deployment strategies.