Dynamic Identification of and Elevated RC Water Tank: Quantifying Rigidity Enhancement trough Steel Bracing and Partition Walls via AVS and FEA

This study investigates the dynamic property variations of a reinforced concrete (RC) elevated water storage tank subjected to sequential structural modifications: steel bracing retrofitting and ground floor partition wall addition. Ambient vibration surveys (AVS) and finite element analysis (FEA) were employed to characterize the structure across three distinct stages: original, retrofitted, and infill walled. Due to the circular configuration of the system, dynamic properties were effectively represented in the cylindrical coordinate system providing a specialized framework for characterizing radial and tangential modal behaviors. Both experimental and numerical analyses consistently identified the first three modes as radial translation, tangential torsion, and radial double curvature, respectively. AVS demonstrated that the first three modal frequencies shifted from 0.755, 1.00, and 2.905 Hz in the original state to 1.56, 3.20, and 5.75 Hz following the retrofit. These trends were corroborated by numerical simulations, which yielded shifts from 0.75, 0.86, and 3.24 Hz to 1.71, 2.46, and 6.66 Hz, respectively. The substantial increase in the second modal frequency, in particular, confirms that the bracing system was most effective in enhancing torsional rigidity. The addition of partition walls was also considered and the impact on the dynamic properties was evaluated. By providing high-fidelity frequency increase factors across both experimental and numerical domains, this study establishes a quantifiable performance metric for rigidity enhancement in water storage systems. The strong correlation between the AVS and FEA results confirms the reliability of the performance metrics, thereby bridging the gap between theoretical analysis and the actualized retrofit of aged utility infrastructure.