Shafqat Ullah

Date of Award

August 2024

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

First Advisor

Iraj H.P Mamaghani

Abstract

Cylindrical steel tanks are an important structural components of various industries, power plants, oil refineries, and other lifeline facilities. These liquid-filled reservoirs are prone to local instability (buckling) when exposed to lateral seismic forces. This thesis aims to study the seismic buckling performance of an empty and partially filled cylindrical steel storage tanks using finite element modeling (FEM) approaches. To validate the accuracy of the FEA ABAQUS software, the cylindrical tanks are considered for both static linear buckling, non-linear, as well as dynamic (seismic non-linear) analysis. A total of 3 cylindrical shells having 1 perfect model without carbon fiber reinforced polymer (CFRP) and the remaining 2 models are strengthened with CFRP are considered for static linear and non-linear buckling analysis. The FE predicted results and previous experimental as well as theoretical solutions are compared. The comparisons shows that FEA accurately predict the buckling load and it is noted that only 9.8% difference between the FE and test results for perfect cylindrical shells. The buckling load obtained from the Nonlinear analysis for Model-1 (CFRP strengthened) is close to the experimental and slightly smaller (5.8%) than the analytical buckling load. Furthermore, the buckling load from linear and nonlinear analysis for Model 2 (CFRP strengthened) is slightly higher than the experimental buckling load and close to analytical solution. To examine the nonlinear seismic analysis of liquid-filled cylindrical tanks, 3 rigid tank models are considered for analysis and the liquid sloshing behavior under seismic excitation is evaluated and the results are compared with test results. The previous numerical and experimental results show that the maximum sloshing elevation for Model-I is about 18.15 mm (1.815 cm) and 15.04 mm (1.504 cm), respectively. The sloshing wave height from the test result is lower than the present FE studies and a total of 13.7% variation is observed. For Model-II (Viscous), both the present study as well as experimental result have close correlation and there is overall 10.3% difference in the results. For Model-II (Damped), the response shows a maximum sloshing height of about 0.84m, which is reduced by 13.4% after applying the damping factors. The FE result is further compared with that of the previous study and there is a small discrepancy (3.4%) between the present and previous research study. Finally, a parametric study is conducted on 4 different steel tanks subjected to input seismic excitations, and the seismic nonlinear behavior of the tanks is evaluated. The analysis shows that the broad storage tanks are more sensitive to large deformation and hoop stresses than slender liquid-filled steel storage tanks. The hydrostatic non-linear analysis shows that maximum stresses are more dominant at the tank base. Furthermore, the peak acceleration of the small tank when subjected to the Northridge, and Sakaria earthquakes is about 0.56g and 0.62g, respectively, when the time reached 10 seconds. The peak response when the tank is subjected to the Sakaria earthquake is slightly higher than the tank exposed to Northridge seismic excitation. The total hydrodynamic pressure response under the Sakaria earthquake is also higher than the pressure response when the storage tank is excited with the Northridge earthquake. The results show that input seismic forces greatly influence the hydrodynamic stresses, which causes the uplift mechanism in steel cylindrical tanks.

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