| Abstract | Nowadays, the importance of health monitoring in substructure becomes an interesting system since there are many advantages such as reduced maintenance costs, early remind damage and ensure serviceability of structure. In this thesis, a scaled pile foundation was performed at the area nearby Environmental Research Station in AIT, and the experimental model which consists of 12 scaled piles was installed with 96 metal-foil strain gauges. When the horizontal vibrations were produced on the top of pile cap by Mass-Spring System in both N-S and E-W directions, the strain response in each pile was measured in order to capture free decay of the specimen. Moreover, Normalized Modal Strain Technique was utilized in this experiment for damage detection. After the consistent of normalized modal strain patterns in two directions were obtained in undamaged state at 36 days and 48 days, the damage was introduced to the soil surround pile No.2. The normalized modal strain signatures were compared between intact and damaged state, this can lead to the damage investigation of the specimen. From this study, the modal strain and modal axial strain pattern were successfully produced, and they can represent the load carrying mechanism of pile foundation. When the damage was introduced to the soil, the normalized modal strain and axial strain signatures are changed accordingly. Therefore, the normalized modal strain approach can be used to detect the damage in pile foundation. In addition, the change of normalized modal strain has a correlation with the damage location and damage severity of pile foundation. Finally, the Winkler Model which was created in ETABS program can be controlled as the similar frequency with the specimen, the change in normalized moment and axial force for all undamaged and damaged conditions were considered in order to compare with experimental model. The results from numerical model show satisfactory agreement with the experimental model in this study. |