Aci-350.3-06.pdf !free! -

ACI 350.3-06 establishes the industry standard for the seismic design of liquid-containing concrete structures, defining procedures for calculating impulsive and convective (sloshing) hydrodynamic forces. The standard provides technical guidelines for designing both circular and rectangular concrete tanks to ensure stability during seismic events. For a preview of the document, see this Scribd publication

  1. Ductility Requirements: The code requires that reinforced concrete structures be designed to provide a minimum level of ductility to absorb seismic energy.
  2. Capacity Design: ACI 350.3-06 emphasizes the importance of capacity design, which involves designing structural members to resist forces that are greater than the expected earthquake loads.
  3. Detailing Requirements: The code provides detailed requirements for reinforcement detailing, including the use of seismic hooks, cross-ties, and confinement reinforcement.
  4. Regular and Irregular Structures: ACI 350.3-06 provides guidelines for designing regular and irregular structures, including the use of modal analysis for irregular structures.
  1. Protect Human Life: By designing structures to resist seismic forces, engineers can help protect human life during earthquakes.
  2. Reduce Economic Losses: By minimizing damage to structures, engineers can help reduce economic losses associated with earthquakes.
  3. Maintain Structural Integrity: The standard ensures that structures can maintain their structural integrity during and after earthquakes, reducing the risk of collapse.
  1. The Impulsive Component: This represents the portion of the liquid that moves in unison with the tank walls. It is located at the bottom of the tank. Because this water is rigidly connected to the structure, it accelerates at the same rate as the ground, generating high-frequency inertial forces. ACI 350.3-06 provides equations to determine the effective mass and center of gravity for this component.
  2. The Convective Component: This represents the remaining liquid, which "sloshes" back and forth. This motion is long-period and low-frequency. While the forces generated are generally lower than the impulsive forces, the convective wave can impact the tank roof (roof uplifting) or cause extensive freeboard requirements.

A. Impulsive Component ($W_i$)

  • What it is: The portion of the liquid that moves in unison with the tank walls. It acts as if it were rigidly attached to the structure.
  • Effect: It creates a high-frequency, high-acceleration force at the base and walls. This is usually the dominant force for short, squat tanks.

6. Discussion

  • ACI 350.3-06’s simplified method closely matches dynamic analysis for impulsive response.
  • Convective contribution is small for this moderate ( H_L / L = 0.33 ) tank, but becomes critical in tall, narrow tanks.
  • The code-prescribed center of pressure heights produce conservative overturning moments.