Stability Analysis of a Real Life Tilted RCC Over Head Reservoir (Tank) considering Soil-Structure and Fluid-Structure Interaction

Tilt and settlement of RCC structures with foundations over alluvial soil of greater Kolkata and surrounding Ganges Flood Basin is a frequent problem with respect to the stability of these structures. The tilt and subsequent distress have a significant effect on the overall stability of the Over Head Reservoirs (Tanks); which also depend on the nature of the supporting soil, Fluid Structure Interaction (FSI). Various NDTs can be performed to assess the condition of the concrete members, but this piecewise assessments may not adequately address the overall stability of the OHRs subjected to various loadings including lateral seismic forces, particularly for a tilted one. Thus, numerical analysis of the tilted OHR is significantly important to assess its overall stability considering its global behaviour. The present numerical study aims to evaluate the effect of the tilt on the overall stability of a real life existing RCC OHR supported on frame staging. The increase in design reinforcement demand and lateral displacement at crown top level are compared to assess the effect of tilt from the Limit State of Collapse and Limit State of Serviceability points of view. The global effect of the tilt is studied based on the changes of its fundamental period of vibrations of the OHR. Subsequently, Pushover analysis is also performed to evaluate the effect of the tilt on the various parameters e.g. base shear capacity, inelastic displacement at crown top level, global ductility. The vulnerability index based on the pushover analysis results are also compared to ascertain the effect of the tilt. Soil-Structure Interaction and Fluid-Structure Interaction have been duly considered in the Finite Element models on SAP2000 platform to study the effect of tilt on the OHR stability. It is found that the tilt plays a great role on the overall stability and safety of the frame staging OHR, which further get aggravated due to softer supporting soil and considering Fluid-Structure Interactions. The proposed stability analysis of this case study seems to have a great potential for its practical application in safety evaluation and retrofit of existing OHRs subjected to tilt.