Online Manuals RFEM 6 / RSTAB 9 | Concrete Foundation

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Ann-Kathrin Dannwerth, B.Sc.

2024-07-11

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Overview

Add-on Concrete Foundation

Theoretical Principles

Design Specifications

Design Properties of Single Foundations

Design

Results

Documentation

Sliding

When verifying sliding, it is checked whether the horizontal actions acting parallel to the foundation base can be adequately resisted by the available resistance. A risk of sliding exists if the design value of the horizontal action is greater than the design value of the resistance to sliding. According to EN 1997-1 [1] 6.5.3, failure by sliding in the base plane must be verified if the load vector is not normal to this plane.

EN 1997-1: Sliding

Determination of actions and resistance The governing action is the resultant horizontal force H_d in the foundation base. The resistance to sliding comprises the following components:

Friction resistance between the foundation base and the subsoil
passive earth pressure, if applicable

In the consolidated state, the design value of the shear resistance is calculated with the design value of the base friction angle:

R_{d} = {V^{'}}_{d} \cdot \tan δ_{d}

Shear Resistance in Drained State

In the unconsolidated state, the effective base area A' is calculated. The design value of the shear resistance is determined using the design value of the undrained cohesion c_u,d:

R_{d} = A^{'} \cdot c_{u, d}

Shear Resistance in Undrained State

Optionally, the passive earth pressure can be taken into account:

σ_{h, t} = k_{p, h} (γ_{d} \cdot z_{o b e n} + q_{d}) + 2 \cdot {c^{'}}_{d} \cdot \sqrt{k_{p, h}}

σ_{h, b} = k_{p, h} (γ_{d} \cdot z_{u n t e n} + q_{d}) + 2 \cdot {c^{'}}_{d} \cdot \sqrt{k_{p, h}}

Top and Bottom Horizontal Passive Earth Pressure

R_{p, x} = \frac{σ_{h, t} + σ_{h, b}}{2} \cdot t \cdot w_{x}

R_{p, y} = \frac{σ_{h, t} + σ_{h, b}}{2} \cdot t \cdot w_{y}

Resisting Force of Soil Layer in x- and y-Directions

Verification The verification of sliding is carried out by comparing the action and the resistance:

H_{d} \leq R_{s, d} + R_{p, d}

Sliding According to EN 1997-1 (Taking Passive Earth Pressure into Account)

IBC 2021 / ACI 318-19 (ASD): Sliding

Purpose of the verification

The sliding verification checks whether the horizontal forces acting on the foundation do not exceed the available sliding resistance.

Sliding resistance

The total sliding resistance comprises

friction resistance at the foundation base
passive earth pressure resistance

\begin{matrix} R_{total} = R_{friction} + R_{passive} \\ R_{friction} = μ \cdot P \end{matrix}

μ	Friction coefficient [-]

Sliding resistance

The friction coefficient μ, the passive earth pressure resistance R_passive, and the required safety factor Φ_sliding,lim can be defined in the geotechnical design configuration. Alternatively, the passive earth pressure resistance can be determined automatically according to Coulomb's earth pressure theory based on the soil parameters defined in the configuration.

Safety factor

Φ_{sliding} = \frac{R_{total}}{H}

H	horizontal force acting on the foundation [kip]

Safety coefficient - Sliding

Utilization ratio

η = \frac{Φ_{sliding, \lim}}{Φ_{sliding}}

Utilization ratio – sliding

Software configuration

The following parameters can be defined in the geotechnical design configuration:

Friction coefficient μ
Passive earth pressure resistance R_passive
Required safety factor Φ_sliding,lim

Alternatively, the passive earth pressure resistance can be determined automatically according to Coulomb's earth pressure theory.

References

European Committee for Standardization (CEN). (2014). Eurocode 7: Geotechnical Design – Part 1: General Rules, EN 1997-1:2014-03. Berlin: Beuth Verlag GmbH.

Parent Chapter

External stability - Geotechnical design