Investigation of structural behaviour in cylindrical steel silo structures with sloshing effect under different foundation conditions

Within the scope of this thesis study, dynamic time-history analyses were performed using solid models with included Fluid-Structure-Soil Interaction (FSSI) to investigate the seismic behavior of cylindrical steel liquid storage silos. The study aims to compare the behaviour of these soil models against the fixed-base assumption, which is commonly used in design codes, under various parameters including different tank diameters (10 m, 20 m, and 40 m), fill ratios (35%, 70%, and 100%), soil relative densities (50% and 85%), foundation geometries (square and cylindrical), and pile length-to-diameter (15Ld, 30Ld) ratios. The analyses indicated that the most critical system behaviour generally occurs at the 70% filling ratio. This level was identified as the most challenging fill ratio for the system about deformations, hydrodynamic effects and stress occurrences. The deformed shapes indicate that while maximum stresses occurred near the base due to hydrostatic effects, maximum deformations occurred at higher elevations due to convective (sloshing) effects. Moreover, as the tank diameter increased (from 10m to 40m), the wave effect propagation on the silo wall has diminished, causing non-uniform deformations. The silo diameter is a significant variable for SSI on wall stresses. While soil-interactive models produced higher stresses than fixed-base models for 10 m diameter silos, the soil provided a more advantageous condition for 20 m and 40 m diameter tanks. These findings demonstrate that the uniform fixed-base assumption and load amplification factors used in current regulations lead to an approach that is overly conservative and uneconomical for large-diameter tanks, while potentially overlooking critical conditions for small-diameter tanks. Soil-interactive solutions vary based on foundation conditions and structural dimensions; they can exhibit 30-60% less stress than fixed-base solutions, whereas regulatory coefficients increase the fixed-base results by 15-20%, therefore sacrificing economy. It is believed that performing realistic Fluid-Structure-Soil Interaction analyses is of critical importance in the design of liquid storage structures, especially for varying diameters and filling ratios. In addition, more appropriate designs can be achieved by updating current regulations to facilitate more economical solutions.