How is the bearing pressure check performed in Advance BIM Designers

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Bearing pressure check (Eurocode)

Note: This check has specific characteristics for countries using the Eurocode.

This verification is based on the assumptions defined in Design Assumptions > Norm dialog and in the Soil Profile dialog.

The considered design approach is DA-1 (Design Approach 1).

The contact pressure distribution is rectangular (EC7 - Annex D).

The value of the net strength of the soil in the shallow foundation Rv is calculated. The inclination factors should be taken into account.

The inclination of the foundation base to the horizontal: 0.00° Soil behavior: cohesive or intermediate soil

Drained conditions (water level not defined)

The following inequality shall be satisfied:

Ground failure resistance: [(6.5.2.1) from EN 1997-1]

Vd ≤ Rd

where:

Vd is the design value of the effective vertical load, or component of the total action acting normal to the foundation base (self-weight + vertical load)

The value defined for V = 220 kN

The forces are defined in relation to the top surface of the footing.

Note: To generate combinations, the program reduces all forces in relation to the bottom surface of the footing.

Example:

For combination +1x[1G]:

V = Vdefined + footing selfweight = Vdefined + L × B × H × ɣreinforced concrete = 220 + 1.5 × 1.5 × 0.5 × 25 V = 248,125 kN (+1x[G])

Mx = Mxdefined - Hy × H = 40 - 30 × 0.5 = 25 kNm My = Mydefined + Hy × H = 40 + 30 × 0.5 = 55 kNm Hx = Hxdefined = 30 kN

Hy = Hydefined = 30 kN

The combination used for the bearing pressure check is ULS102 +1.35x[1 G]

Vd = 1.35 × V(+1x[1G]) = 1.35 × 247.59 = 334.25 kN

Vd = 334.25 kN

Rd is the design value of bearing capacity

A’ = effective foundation area calculation (Annex D1 from EN 1997-1) A' = B' × L' = (B - 2 × eB)×(L-2 × eL)

B' = the effective foundation width (A’ in the Geometry > Footing dialog)

L' = the effective foundation length (B' in the Geometry > Footing dialog) eB, eL= eccentricities on both directions

B' = 1.50 - 2 × 0.222 = 1.056 m

L' = 1.50 - 2 × 0.101 = 1.298 m

Since B’ < L’, it should be concluded that:

B' = 1.056 m L' = 1.298 m

A' = 1.056 × 1.298 = 1.371 m2

qult,k = ultimate bearing pressure (Annex D4 from EN 1997-1) in drained conditions

Bearing capacity factors as function of φ:

φ (effective angle of shearing resistance)

This parameter can be defined in the Soil Profile dialog, in the row corresponding to the soil layer from the footing base.

Base inclination correction factors:

α (inclination of a foundation base to the horizontal)

This parameter can be defined in the Design Assumptions > Norm dialog, in the "Characteristic efforts" section.

Shape correction factors:

H (load inclination, caused by a horizontal load)

where:

In cases where the horizontal load component acts in a direction forming an angle Ɵ with the direction of L', m may be calculated by:

For these factors to be taken into account, the user must check the "Inclined loading" option in the Design Assumptions > Norm dialog, in the "Characteristic efforts" section. Otherwise, the value for all these factors will be considered equal to 1.

c' (effective cohesion in drained conditions)

This parameter can be defined in the Soil Profile dialog, in the row corresponding to the soil layer from the footing base.

q' (the design effective overburden pressure at the level of the foundation base)

ɣ’ = the design effective weight density of the soil below the foundation top level. This parameter can be defined in the Soil Profile dialog, in the row corresponding to the soil layer/layers above the footing base.

The design effective weight density of the soil layer/layers from above the foundation base level can be individually set for drained or undrained conditions.

In the current example the calculation is performed in drained conditions

D (the embedment depth according to Annex D1 from EN 1997-1)

The "Altitude" parameter represents the altitude of the top foundation level measured from the top level of the first soil layer and can be defined in the Levels dialog, in the "Footing level" section.

qult,k can now be calculated:

Vd = 334.25 kN < Rd = 740 kN

The condition is satisfied.

Undrained conditions

To perform a calculation under undrained conditions the user must access the Soil Profile dialog > "Ground water" section, specify the top level and/or the bottom level of the ground water, and check the option "Perform a calculation under undrained conditions".

For this example, we will only consider a top level of ground water at a 300 mm depth. The footing dimensions and the others assumptions remain unchanged.