EN 1997-1: Buoyancy
The verification against buoyancy must be performed according to EN 1997-1 [1] 2.4.7.4 such that the design value of the combination of destabilizing permanent and variable vertical actions Vdst,d is less than or equal to the sum of the design value of the stabilizing permanent vertical actions Gstb,d and the design value of any additional resistance Rd against buoyancy.
IBC 2021 / ACI 318-19 (ASD): Uplift
Purpose of Verification
The uplift check verifies whether the vertical forces acting on the foundation are sufficient to prevent uplift of the foundation from the load-bearing subsoil. If the total vertical force on the foundation becomes negative, uplift occurs, and the foundation would lose contact with the subsoil.
Verification Principle
The verification is performed by evaluating the total vertical force on the foundation for each load combination:
Pz = Σ vertical forces on the foundation
The uplift condition is satisfied if
If Pz < 0, uplift occurs.
Components of Vertical Load
The total vertical force on the foundation can include the following components:
- applied column loads
- self-weight of the foundation
- self-weight of the column
- weight of soil overburden above the foundation
- vertical components of applied loads
Horizontal loads without a vertical component do not enter the uplift check.
Governing Load Combination
The governing load combination is the one that produces the smallest vertical force Pz. In ASD design according to ASCE 7, the minimum stabilizing vertical load typically occurs in load combinations with reduced self-weight (e.g., 0.60 D).
Software Configuration
The uplift check is automatically performed for all defined load combinations of the selected design situation. The vertical loads acting on the foundation are taken from the defined load cases. Additional vertical loads such as foundation self-weight, soil overburden, and groundwater effects can be activated in the load case settings under the "Concrete Foundations" tab.