Next: Effect of Vertical Excitation Up: Unanchored Tank Response Previous: Effect of Plasticity
The uplift mechanism that governs the response of unanchored tanks is influenced by the thickness of the base plate. Tanks with thinner base plate uplift more and consequently more axial stresses are developed at the bottom of the tank shell. In addition, decreasing the thickness of the base plate reduces the rocking stiffness and consequently lengthens the rocking period. This causes developed hydrodynamic forces to be slightly less than those of tanks with thicker base plate. Table (5.9) shows the response of the unanchored tanks to El Centro and Northridge earthquakes, respectively, assuming that the base plate thickness is 0.5 inch and considering the large deflection effect.
Table 5.9: Response of Unanchored Tanks with Reduced Base Plate Thickness - Large Deflection Assumption| Response Parameter | El Centro Record | Northridge Record | | | Broad | Tall | Broad | Tall | | Top Lateral Acceleration | 1.22g | 0.78 g | 2.09 g | 0.80 g | | Top Lateral Deflection (in) | 1.75 | 6.46 | 1.89 | 9.9 | | Total OTM / WR | 0.104 | 0.358 | 0.156 | 0.430 | | Wall OTM / WR | 0.039 | 0.304 | 0.055 | 0.345 | | Base Shear / W | 0.147 | 0.220 | 0.214 | 0.288 | | Base Axial Stress (Ksi) | -1.64 | -7.03 | -2.36 | -7.40 | | Axial Stress at 0.25H (Ksi) | -0.76 | -5.15 | -1.36 | -5.40 | | Hoop Stress at 0.25H (Ksi) | 16.39 | 10.82 | 17.71 | 11.60 | | Maximum Uplift Displacement (in) | 0.46 | 1.71 | 0.727 | 2.96 | | Minimum Contact Area | 0.768 | 0.646 | 0.756 | 0.622 |
|
Next: Effect of Vertical Excitation Up: Unanchored Tank Response Previous: Effect of Plasticity A. Zeiny
2000-09-06