Strengthening effects of spiral stairway on the buckling behavior of metal tanks under wind and vacuum pressures

• Strengthening effects of stairway on buckling behavior of metal tanks are studied.
• Under wind pressure, spiral stairways improve buckling strength of tank wall.
• Under vacuum pressure, the stairway significantly changes buckling mode of tank.
• Effect of stairway on buckling resistance of tanks subjected to wind pressure increases as H/D increases.
• Effect of stairway on open-top tanks can be much higher than those obtained from conical roof tanks.

Steel cylindrical tanks are formed by very thin-walled shells and as typical thin-walled structures, they are very sensitive to buckling under external pressures, especially when they are empty or at low liquid level. Results of numerical investigations on the effects of spiral stairway on the buckling behavior of ground based steel cylindrical liquid storage tanks subjected to both wind and vacuum pressures are presented. It is concluded that by choosing appropriate circumferential position for stairway, considering regional prevailing wind direction, designers can use the noticeable amount of added strength arising from stairway as a safety margin. In other words, it seems that the spiral stairway acts as an oblique stiffener on the tank wall. Contrary to the case of wind loading, the stairway has negligible effect on buckling resistance of tanks under vacuum pressure. However, it changes the buckling modes of tank significantly under vacuum loading.