Online Manuals RFEM 6 / RSTAB 9 | Concrete Foundation

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006025

Hedi Boukraa, M.Sc.

2025-06-12

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Overview

Add-on Concrete Foundation

Theoretical Principles

Design Specifications

Design Properties of Single Foundations

Design

Results

Documentation

Geometry

In the Geometry tab, you define the dimensions of the foundation slab and the bucket.

Concrete Foundations | Bucket Foundations, Tab Geometry

The following table lists the parameters used to describe the geometry of the slab, bucket, and eccentricity.

Variable	Label
w_x / w_y	Foundation slab dimension in the x- and y-direction, respectively
t	Foundation slab thickness
h	Bucket height
d	Embedment depth of the column
t_tx / t_ty	Bucket wall thickness at the top in the x- and y-direction, respectively
a_tx / a_ty	Column clearance at the top in the x- and y-direction, respectively
t_bx / t_by	Bucket wall thickness at the bottom in the x- and y-direction, respectively
a_bx / a_by	Column clearance at the bottom in the x- and y-direction, respectively
α_x / α_y	Inner wall inclination in the x- and y-direction, respectively
e_x / e_y	Eccentricity in the x- and y-direction, respectively
c_x / c_y	Column dimension in the x- and y-direction, respectively

Info

The column dimensions cannot be adjusted here. They can only be changed in the cross-section dialog box of the corresponding member.

Using the button below the system sketch, you can display the dynamic model with the dimensions directly in the tab.

Bucket Foundations, Tab Geometry with Dynamic Model

Minimum Dimensions

Certain minimum dimensions must be maintained to ensure the correct geometric execution of the bucket foundation.

Embedment Depth

The embedment depth must not be greater than the height of the bucket.

d \leq h

Bucket Foundations | Maximum Embedment Depth of Column

Upper Bucket Wall Thickness

The minimum thickness of the upper bucket wall results from the maximum of four individual minimum values. The greatest of these thicknesses defines the required wall thickness:

The bucket wall (depending on the stirrup arrangement type) must be designed so that the mandrel diameter, the diameter of the statically required vertical stirrups in the x-direction, the diameters of the horizontal stirrups in the y-direction (inside and outside), as well as twice the concrete cover can be sufficiently taken into account:

\{\begin{cases} 2 \cdot (c_{k} + d_{m, v, x} + d_{s, v, x}) + d_{s, h, x} + \max (d_{s, h, outer}, d_{s, h, y}) + d_{s, v, y} \leq t_{tx} & stirrups enclosing the column \\ 2 \cdot (c_{k} + d_{m, v, x} + d_{s, v, x}) + d_{s, h, x} + \max (d_{s, h, x}, d_{s, h, y}) + d_{s, v, y} \leq t_{tx} & stirrups lying completely in the bucket wall \end{cases}

c_k	Concrete cover of the bucket wall
d_m,v,x	Minimum mandrel diameter of the vertical static stirrups in the x-direction
d_s,v,x	Diameter of the vertical static stirrup
d_s,h,x	Diameter of the horizontal stirrup in the X-direction (inside)
d_s,h,outer	Diameter of the outer horizontal stirrup
d_s,h,y	Horizontal stirrup in the y-direction
d_s,v,y	Diameter of the vertical stirrup in the y-direction

Bucket Foundations | Minimum Dimensions of Wall Thickness (1)

The second condition depends on the width of the column and the column clearance (top and bottom):

\frac{(2.0 \cdot a_{tx} + c_{x}) + (2.0 \cdot a_{bx} + c_{x})}{6.0} \leq t_{tx}

Bucket Foundations | Minimum Dimensions of Wall Thickness (2)

The third condition is a geometric specification that depends on the width of the column:

\frac{c_{x} + 15 cm}{3} \leq t_{tx}

Bucket Foundations | Minimum Dimensions of Wall Thickness (3)

To ensure an absolute minimum limit, a minimum wall thickness of 10 cm is applied regardless of the reinforcement and geometry.

10 cm \leq t_{tx}

Bucket Foundations | Minimum Dimensions of Wall Thickness (4)

Info

The minimum dimensions of the wall thickness in the y-direction must be considered analogously to those in the x-direction.

Further Minimum Dimensions

\{\begin{cases} (t_{tx} + a_{tx}) = (t_{bx} + a_{bx}) \\ (t_{t y} + a_{t y}) = (t_{b y} + a_{b y}) \end{cases}

Bucket Foundations | Bucket Width Condition

These relationships ensure that the total width of the bucket at the top and bottom is identical in each direction.

\{\begin{cases} (t_{tx} \leq t_{bx}) & (a_{tx} \geq a_{bx}) \\ (t_{t y} \leq t_{b y}) & (a_{t y} \geq a_{b y}) \end{cases}

Bucket Foundations | Bucket Inner Wall Condition

All the relationships mentioned ensure that

the wall thickness at the bottom is at least as large as the wall thickness at the top, and
the column clearance at the top is at least as large as the column clearance at the bottom.

The inner wall of the bucket can either be vertical or inclined outwards. An inward inclination is prevented.

Rotation of Foundation via Nodal Support

Rotation of a foundation about the Z-axis is carried out via the local coordinate system of the associated nodal support. Direct rotation of the foundation is not possible. A prerequisite is that the local z-axis of the nodal support is parallel to the global Z-axis.

Create a user-defined local coordinate system and assign it to the nodal support. The foundation adopts the orientation of this local coordinate system.

Editing Local Coordinate System of Nodal Support

The orientation of the column has no influence on the alignment of the foundation. Rotation of the column about the global Z-axis can occur independently of the foundation and is not necessarily required for the design of the foundation, although a column orientation parallel to the global Z-axis is required for the use of foundations.

Parent Chapter

Bucket Foundation