Concrete below base plate is simulated by Winkler subsoil with uniform stiffness, which provides the contact stresses. The average stress at the loaded area in contact with base plate is used for compressive check.

### Concrete in compression

The concrete design bearing strength in compression is determined in accordance with S16-14 – 25.3.1 and CSA A23.3 – 10.8. When the supported surface of the concrete is larger than the base plate the design bearing strength is defined as

\[ f_{p,(max)} = 0.85 \phi_c f'_c \sqrt{\frac{A_2}{A_1}} \le 1.7 \phi_c f'_c \]

where:

*ϕ*_{c}=0.65 – resistance factor for concrete*f'*_{c}– concrete compressive strength*A*_{1}– base plate area in contact with concrete surface (upper surface area of the frustum)*A*_{2}– concrete supporting surface (geometrically similar lower area of the frustum having its slopes of 1 vertical to 2 horizontal)

The assessment of concrete in bearing is as follows:

*σ* ≤ *f*_{p(max)}

where:

*σ*– average compressive stress under the base plate

### Transfer of shear forces

Shear loads can be transferred via one of these options:

- Shear lug,
- Friction,
- Anchor bolts.

#### Shear lug

Shear loads are considered to be transferred only via shear lug. Concrete bearing is not checked in software and should be checked by user elsewhere. Shear lug and welds are checked using FEM and weld components.

#### Friction

In case of compressive force, the shear loads can be transferred via friction between a concrete pad and a base plate. The friction coefficient is editable in Code setup.

#### Anchor bolts

If the shear load is transferred via anchor bolts only, the shear force acting on each anchor is determined by FEA and anchor bolts are assessed according to ACI 318-14 as described in following chapters.